Previous weeks

2015

October

Date: 09 October 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Epigenetic Mechanisms of Habit Learning

Speaker: Melissa Malveaz

Abstract: Considerable evidence suggests that instrumental behavior depends on two distinct learning processes; one cognitive, in which the relationship between actions and their consequences is encoded, and one habitual, involving the formation of stimulus-response associations. These processes rely on dissociable neural circuits, but beyond this very little is known about the mechanisms required to form these associative memories. Given the recently ascribed role for epigenetics in memory formation, we examined the role of one such mechanism, histone acetylation, in instrumental learning. Rats were trained to lever press for a food reward and were administered the non-specific histone deacetylase (HDAC) inhibitor sodium butyrate (NaB) immediately following each training session. Following training, devaluation of the food outcome was used to probe cognitive versus habitual control of instrumental behavior. Although both groups learned the task, those rats treated with NaB showed insensitivity to outcome devaluation earlier in training than vehicle-treated rats, suggesting that HDAC inhibition potentiated habit formation. Insensitivity to degradation in the action-outcome contingency was also observed and the potentiation of habit occurred regardless of training schedule (i.e., random interval v. ratio). Systemic HDAC inhibition increased histone H4 lysine 8 acetylation specifically in the dorsal striatum, a major component of the instrumental learning circuit. In follow-up experiments, selective modulation of HDAC3 activity in the dorsolateral striatum was found to be sufficient to modulate the sensitivity of instrumental action to devaluation. These data identify chromatin modification by histone acetylation as an important mechanism in the development of stimulus-response associative memories. Moreover, the results suggest that HDAC inhibition can potentiate habitual over cognitive instrumental learning processes, a finding with important implications for the therapeutic application of HDAC inhibitors.

Date: 02 October 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Deep Learning: What should neuroscientists learn from machine learning?

Speaker: Dean Buonomano

Deep learning LeCun Y, Bengio Y, Hinton G (2015) Nature 521:436-444. http://www.nature.com/nature/journal/v521/n7553/full/nature14539.html <cid:part1.05060107.05080708@ucla.edu>

Human-level control through deep reinforcement learning Mnih V, Kavukcuoglu K, Silver D, Rusu AA, Veness J, Bellemare MG, Graves A, Riedmiller M, Fidjeland AK, Ostrovski G, Petersen S, Beattie C, Sadik A, Antonoglou I, King H, Kumaran D, Wierstra D, Legg S, Hassabis D (2015) Nature 518:529-533. http://www.nature.com/nature/journal/v518/n7540/full/nature14236.html

=September

Date: 25 September 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title:Motor cortex is required for learning but not for executing motor skill

Speaker:Paul Mathews

The motor cortex is often considered the main controller for movement, but a new study shows that well-trained paw movements can be performed with equal precision after lesions of the entire motor cortex; the motor cortex is, however, required for learning a new task in naïve animals.

Paper:http://www.sciencedirect.com/science/article/pii/S0896627315002202?np=y

Perspective: http://www.sciencedirect.com/science/article/pii/S0960982215004364

June

Date: 12 June 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Time Cells in the Hippocampus: a new dimension for mapping memories

Speaker: Helen Motanis (Buonomano Lab)

Recent studies have revealed the existence of hippocampal neurons that fire at successive moments in temporally structured experiences. Several studies have shown that such temporal coding is not attributable to external events, specific behaviours or spatial dimensions of an experience. Instead, these cells represent the flow of time in specific memories and have therefore been dubbed 'time cells'. The firing properties of time cells parallel those of hippocampal place cells; time cells thus provide an additional dimension that is integrated with spatial mapping. The robust representation of both time and space in the hippocampus suggests a fundamental mechanism for organizing the elements of experience into coherent memories. My talk will focus on a series of papers by the Eichenbaum lab showing the involvement of the Hippocampus in the memory of sequence of events Fortin et al. 2002 NatureNeuroscience , Manns et al., 2007 Neuron and the discovery of 'Time cells' Kraus et al., 2013 Neuron , MacDonald et al., 2013 JNS , Eichenbaum 2014 NatureNsReviews.

May

Date: 29 May 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Cell-type-specific sensorimotor processing in striatal projection neurons during goal-directed behavior

Speaker: Tanya Sippy

Speaker Bio: Dr. Sippy started her neuroscience career as an undergraduate at UCLA studying synaptic mechanisms underlying short term plasticity. She then completed her MD and PhD degrees at Columbia University where she became interested how different interneuronal subtypes influence local circuit processing. Afterward, Dr. Sippy completed a postdoctoral fellowship at the EPFL in Lausanne, Switzerland, where she applied the technique of in vivo patch clamp to study the role of striatal neuron subtypes during rewarded behaviors. She is currently at New York University where she is pursuing her residency in the psychiatry research track.

Abstract: A key function of the brain is to interpret incoming sensory information in the context of learned associations in order to guide adaptive behavior. However, the neuronal circuits and causal mechanisms underlying goal-directed sensorimotor transformations remain to be clearly defined for the mammalian brain. The basal ganglia, including the striatum and the dopamine reward system, are thought to be involved in action initiation and selection and their dysfunction is associated with Parkinson’s disease, as well as other brain disorders typically involving sensorimotor deficits. We investigated the role of the striatum in a simple task in which mice learn to lick for water reward in response to a single brief whisker deflection (Sachidhanandam et al., 2013). Mice were trained to detect single deflections of the C2 whisker, and report the deflection by licking a spout to obtain water. Whole-cell recordings revealed strong task-related modulation of membrane potential in the somatosensory striatum. Membrane potential depolarization was significantly larger in hit versus miss trials, correlating with perceptual report. This depolarization has two phases; an early phase corresponding to the sensory stimulation, and a late phase, which we define as the period after the early phase before the animal licks, both of which are larger during hit trials. In addition, in a minority of cells where that fire action potentials, the probability of firing action potentials is higher during hit trials. Interestingly, in response to sensory whisker stimulation, D1R-expressing direct pathway striatal projection neurons transiently depolarized more rapidly and more strongly than D2R-expressing indirect pathway neurons. Transient activity in D1R-expressing neurons could therefore contribute to driving the licking behavior. We tested this hypothesis using optogenetics, finding that transient stimulation of D1R-expressing direct pathway striatal projection neurons, but not D2R-expressing indirect pathway neurons, robustly evoked licking in trained mice. Our results are consistent with learned, goal-directed sensorimotor transformations resulting from enhanced signaling in D1R-expressing striatal projection neurons of the direct ‘go’ pathway.

Background papers: http://www.nature.com/nature/journal/v521/n7552/full/nature14225.html

Date: 15 May 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: AMPA receptor Phosphorylation and Synaptic Plasticity

Speaker: Tom O'Dell

Phosphorylation-dependent changes in the activity and trafficking of AMPA-type glutamate receptors is thought to have a crucial role in both LTP and LTD. Moreover, PKA-mediated phosphorylation of AMPA receptor GluA1 subunits is responsible for the enhancement of LTP induction and learning induced by modulatory neurotransmitters such as norepinephrine. Recent findings from Yasunori Hayashi’s laboratory using a novel, quantitative biochemical technique (Phos-tag SDS-PAGE) to measure the stoichiometry of AMPA receptor phosphorylation indicate, however, that very few, if any, AMPA receptors are phosphorylation at sites implicated in synaptic plasticity. In my talk I will discuss the implications of the new findings from Hayashi’s lab and describe the results from recent experiments in our lab addressing this question.

Paper: http://www.cell.com/neuron/abstract/S0896-6273%2814%2901078-2

Date: 1 May 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Artificial Association of Pre-stored Information to Generate a Qualitatively New Memory

Speaker: Sarah Hersman (Fanselow Lab)

Memory is thought to be stored in the brain as an ensemble of cells activated during learning. Although optical stimulation of a cell ensemble triggers the retrieval of the corresponding memory, it is unclear how the association of information occurs at the cell ensemble level. Using optogenetic stimulation without any sensory input in mice, we found that an artificial association between stored, non-related contextual, and fear information was generated through the synchronous activation of distinct cell ensembles corresponding to the stored information. This artificial association shared characteristics with physiologically associated memories, such as N-methyl-D-aspartate receptor activity and protein synthesis dependence. These findings suggest that the association of information is achieved through the synchronous activity of distinct cell ensembles. This mechanism may underlie memory updating by incorporating novel information into pre-existing networks to form qualitatively new memories.

Paper: http://www.cell.com/cell-reports/abstract/S2211-1247%2815%2900270-3

Background Material:

Optogenetic stimulation of memory engram leading to memory retrieval:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3331914/

Creation of artificial memories:

http://www.ncbi.nlm.nih.gov/pubmed/22442487

http://www.sciencemag.org/content/341/6144/387

http://www.ncbi.nlm.nih.gov/pubmed/25322798

April

Date: 24 April 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Some Observations on Biological Noise

Speaker: Walt Babiec (O'Dell Lab)

Behavioral and anatomical studies support a functional segmentation between dorsal and ventral hippocampus. The dorsal (posterior in primates) hippocampus performs primarily cognitive functions. The ventral (anterior in primates) relates to stress, emotion, and affect. Perhaps to help in mediating these different roles, Schaffer collateral (SC) fiber synapses onto pyramidal cells (PCs) in the CA1 region of the dorsal and ventral hippocampus exhibit striking differences in both short-term and long-term plasticity. Importantly, evoked and spontaneous synaptic transmission may involve distinct molecular mechanisms, pools of presynaptic vesicles, and postsynaptic receptors. For this reason, we’ve been examining evoked and spontaneous transmission at SC-PC excitatory synapses in CA1 of dorsal and ventral hippocampus to determine whether the properties of spontaneous transmitter release also differ along the septotemporal axis of the hippocampus. Given the robust differences in short-term plasticity at excitatory synapses in the CA1 region of dorsal and ventral hippocampus, we’ve been particularly interested in examining whether the higher probability of transmitter release at ventral synapses (suggested by reduced paired-pulse facilitation compared to dorsal hippocampus) is associated with higher levels of spontaneous transmitter release. I’ll be talking about some observations we’ve found so far.

Background Material:

Fanselow & Dong: http://www.sciencedirect.com/science/article/pii/S0896627309009477

Kavalali: http://www.nature.com/nrn/journal/v16/n1/full/nrn3875.html

Kaeser & Regehr: http://www.annualreviews.org/doi/full/10.1146/annurev-physiol-021113-170338?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed&

Date: 17 April 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Branch-specific dendritic Ca2+ spikes cause persistent synaptic plasticity

Speaker: Anu Goel (Portera Lab)

The brain has an extraordinary capacity for memory storage, but how it stores new information without disrupting previously acquired memories remains unknown. Here we show that different motor learning tasks induce dendritic Ca2+ spikes on different apical tuft branches of individual layer V pyramidal neurons in the mouse motor cortex. These task-related, branch-specific Ca2+ spikes cause long-lasting potentiation of postsynaptic dendritic spines active at the time of spike generation. When somatostatin-expressing interneurons are inactivated, different motor tasks frequently induce Ca2+ spikes on the same branches. On those branches, spines potentiated during one task are depotentiated when they are active seconds before Ca2+ spikes induced by another task. Concomitantly, increased neuronal activity and performance improvement after learning one task are disrupted when another task is learned. These findings indicate that dendritic-branch-specific generation of Ca2+ spikes is crucial for establishing long-lasting synaptic plasticity, thereby facilitating information storage associated with different learning experiences.

Date: 10 April 2015 (YOUNG INVESTIGATOR SEMINAR)

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Corticostriatal Plasticity in Reward History and Addiction

Speaker: Andrew Thompson (Izquierdo Lab)

The striatum is important for learning from the decisions we make and altering behavior to maximize reward acquisition rate. Through dopaminergic modulation of the direct and indirect pathways, the striatum serves as a final ‘gate’ between impulse and action. Drugs of abuse such as methamphetamine exert their rewarding effects by increasing dopamine release to the striatum, reinforcing the preceding behaviors. Corticostriatal long-term potentiation occurs when three events coincide: presynaptic activation, postsynaptic activation, and time-locked phasic dopamine signaling. Brain derived neurotrophic factor (BDNF) is released in an activity-dependent manner from cortical input neurons, triggering a phosphorylation event at the tropomyosin-related kinase B (TrkB) receptor, activating intracellular signaling pathways which strengthen the associated synapse. Therefore, periods of high and low TrkB signaling in the striatum create critical windows for reward learning. Here we show that methamphetamine and exercise alone are both able to transiently increase TrkB signaling in the rat striatum, but that pre-exposure to methamphetamine blocks the effect of exercise on this measure.

Date: 03 April 2015 (YOUNG INVESTIGATOR SEMINAR)

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Rodent Hippocampal Activity in Real and Virtual Environments

Speaker: Zahra M. Aghajan (Mehta Lab)

The hippocampus is linked to our ability to form episodic memories by providing a spatial cognitive map together with the content of experiences. In rodents, the focus has largely been on the role of hippocampus in the representation of space but despite decades-long research, the underlying mechanisms remain unknown. It has been shown that multiple sensory and motor inputs reach the hippocampus and can modulate its activity. In real world (RW) environments however, the contributions of these inputs are confounded. Thus, to dissociate these contributions and thereby elucidate the mechanisms of spatial selectivity, we used a virtual reality (VR) setup.

We found comparable levels of hippocampal spatiotemporal selectivity on linear tracks in RW and VR. In contrast, during random foraging in two-dimensions, spatial selectivity was severely diminished in VR. Nevertheless, most spikes occurred within ~2-s-long hippocampal motifs—with similar structure to that in RW—within which hippocampal temporal code was intact, demonstrating a decoupling between the spatial and the temporal codes. Further, additional experiments and analysis revealed significant directional selectivity in the hippocampus in RW and VR. Notably, contrary to the impairment of spatial selectivity in VR, the degree of directional selectivity was identical in both worlds and determined by the angular information contained in the visual cues. Taken together, these results suggest that while visual cues alone are insufficient to generate a stable localized representation in the spatial domain, they are sufficient to elicit—and play a causal role in—hippocampal directional selectivity.

Relevant papers:

http://www.sciencemag.org/content/340/6138/1342.full

http://www.nature.com/neuro/journal/v18/n1/full/nn.3884.html

http://biorxiv.org/content/early/2015/03/28/017210

March

Date: 20 March 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Ensemble dynamics in the lateral amygdala encode the formation of new fear memories

Speaker: Benjamin Grewe (Golshani Lab)

Previous research has investigated molecular, synaptic and cellular substrates of fear memory in the basolateral amygdala (BLA), but neural ensemble mechanisms underlying fear learning remain unknown. Using miniaturized imaging techniques we recorded neuronal ensembles in the BLA of freely moving mice and followed ensemble coding of conditioned and unconditioned stimuli throughout a multi day fear learning paradigm. We were able to show how aversive experiences during fear learning change the ensemble code of a neutral conditioned stimulus, to incorporate elements of aversive coding.

Date: 06 March 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: A temporal shift in the circuits mediating retrieval of fear memory

Speaker: Michael Einstein (Golshani Lab)

Fear memories allow animals to avoid danger, thereby increasing their chances of survival. Fear memories can be retrieved long after learning, but little is known about how retrieval circuits change with time. Here we show that the dorsal midline thalamus of rats is required for the retrieval of auditory conditioned fear at late (24 hours, 7 days, 28 days), but not early (0.5 hours, 6 hours) time points after learning. Consistent with this, the paraventricular nucleus of the thalamus (PVT), a subregion of the dorsal midline thalamus, showed increased c-Fos expression only at late time points, indicating that the PVT is gradually recruited for fear retrieval. Accordingly, the conditioned tone responses of PVT neurons increased with time after training. The prelimbic (PL) prefrontal cortex, which is necessary for fear retrieval, sends dense projections to the PVT. Retrieval at late time points activated PL neurons projecting to the PVT, and optogenetic silencing of these projections impaired retrieval at late, but not early, time points. In contrast, silencing of PL inputs to the basolateral amygdala impaired retrieval at early, but not late, time points, indicating a time-dependent shift in retrieval circuits. Retrieval at late time points also activated PVT neurons projecting to the central nucleus of the amygdala, and silencing these projections at late, but not early, time points induced a persistent attenuation of fear. Thus, the PVT may act as a crucial thalamic node recruited into cortico-amygdalar networks for retrieval and maintenance of long-term fear memories.

February

Date: 27 February 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Strategies for Early Detection and Treatment of Neurodegeneration

Speaker: Gary Small

Background Papers: Small et al., 2008 Bookheimer et al., 2008 Chen et al., 2014 Small et al., 2013 Small et al., 2012 Small et al., 2006

Date: 20 February 2015 </font> YOUNG INVESTIGATOR SEMINAR

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Co-allocation of neural ensembles links different memories across time

Speaker: Denise Cai (Silva Lab) While there have been significant advances in the understanding of the mechanisms underlying the storage of single memories, real-world memories, however, involve the integration of multiple memories across time, with one memory affecting how another is processed and stored. Recent studies find that virally increasing neuronal excitability changes the probability of that neuron to participate in a memory trace (i.e. cellular allocation). This leads to the prediction that the induction of one memory will trigger a time-dependent increase in excitability that will then affect the cellular allocation of a subsequent memory, thus sharing a neural ensemble will link the two memories across time. Using in vivo calcium imaging (with miniaturized fluorescent microscopes in freely behaving mice), the TetTag transgenic system, we found that a given contextual memory can affect which CA1 neurons store a subsequent contextual memory 5 hours later (when there is increased excitability in the neurons participating in the first memory) but not 7 days later. The CA1 neuronal ensembles representing each of the two memories co-allocate significantly (>20% above chance) when they are separated by 5 hours but not by 7 days. Interestingly, we found evidence that the co-allocation between cellular ensembles also led to contextual linking as fear from a context paired with shock was generalized to a non-shocked context when the two episodes were spaced by 5 hours, but not by 7 days. We found enhanced behavioral memory for the second episode, when spaced 5 hours from the first episode but not when spaced by 7 days, presumably due to the transient increase in excitability. Finally, our studies in older mice, known to have decreased excitability in CA1, revealed a disruption of co-allocation processes that link memories across time. Altogether, these results provide important insights into how intrinsic changes in excitability can serve to temporally and contextually link multiple memories.

Background Papers: Silva et al., 2009 Rogerson et al., 2014

Date: 13 February 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Activity-Induced Nr4a1 Regulates Spine Density and Distribution Pattern of Excitatory Synapses in Pyramidal Neurons

Speaker: Shivan Bonanno (Martin Lab)

Excitatory synapses occur mainly on dendritic spines, and spine density is usually correlated with the strength of excitatory synaptic transmission. We report that Nr4a1, an activity-inducible gene encoding a nuclear receptor, regulates the density and distribution of dendritic spines in CA1 pyramidal neurons. Nr4a1 overexpression resulted in elimination of the majority of spines; however, postsynaptic densities were preserved on dendritic shafts, and the strength of excitatory synaptic transmission was unaffected, showing that excitatory synapses can be dissociated from spines. mRNA expression profiling studies suggest that Nr4a1-mediated transcriptional regulation of the actin cytoskeleton contributes to this effect. Under conditions of chronically elevated activity, when Nr4a1 was induced, Nr4a1 knockdown increased the density of spines and PSDs specifically at the distal ends of dendrites. Thus, Nr4a1 is a key component of an activity-induced transcriptional program that regulates the density and distribution of spines and synapses.

Yelin Chen, Yuanyuan Wang, Ali Ertürk, Dara Kallop, Zhiyu Jiang, Robby M. Weimer, Joshua Kaminker, Morgan Sheng

Date: 06 February 2015 YOUNG INVESTIGATOR SEMINAR

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Dissociable profiles of generalization/discrimination in human hippocampus during visual associative memory retrieval

Speaker: Natalie De Shetler (Rissman Lab)

A number of recent high-resolution functional magnetic resonance imaging (hr-fMRI) studies have identified differential discrimination and generalization responses in hippocampal subfields. The combined CA3 / dentate gyrus (CA3DG) region responds similarly to novel stimuli and close lure images of previously viewed stimuli, a discrimination sometimes equated to pattern separation processes. Conversely, activity in CA1 to these same lure images tends to be comparable with that elicited by repeated stimuli. In a parallel line of research into hippocampal subfield functions, several studies have found that the CA1 region is particularly sensitive to whether events match or mismatch one’s memory-based expectations (e.g., associative novelty). However, the expression of these effects may differ according to whether subjects are explicitly oriented towards the goal of detecting mnemonic targets or whether the detection is incidental. We conducted a hr-fMRI study to determine if the previously described profile of mnemonic discrimination in CA3DG and generalization in CA1 persist in an explicit associative memory recall task. Each trial of our task required subjects to retrieve a previously learned visual associate in response to an arbitrarily paired verbal cue stimulus, hold the retrieved memory in mind for a brief interval, and then evaluate whether a visual probe stimulus was the same, similar, or dissimilar from the studied associate. In both CA3DG and CA1 we found match enhancement effects (same > novel). Consistent with prior work, CA3DG responded comparably to lures and novels (discrimination), and CA1 responded comparably to lures and repeated targets (generalization). Importantly, our results reflect dissociable profiles to task conditions. CA3DG discriminated old from new irrespective of the task relevance context, showing the same degree of match enhancement to all repeated images, regardless of whether they were correctly or incorrectly paired; in contrast, CA1 generalized only for repeated stimuli with correct item pairings, while responding to incorrectly paired repeats as if they were novel stimuli.

January

Date: 30 January 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Cerebellar plasticity and motor learning deficits in a copy-number variation mouse model of autism

Speaker: Katrina Choe (Otis Lab)

A common feature of autism spectrum disorder (ASD) is the impairment of motor control and learning, occurring in a majority of children with autism, consistent with perturbation in cerebellar function. Here we report alterations in motor behaviour and cerebellar synaptic plasticity in a mouse model (patDp/+) for the human 15q11-13 duplication, one of the most frequently observed genetic aberrations in autism. These mice show ASD-resembling social behaviour deficits. We find that in patDp/+ mice delay eyeblink conditioning—a form of cerebellum-dependent motor learning—is impaired, and observe deregulation of a putative cellular mechanism for motor learning, long-term depression (LTD) at parallel fibre-Purkinje cell synapses. Moreover, developmental elimination of surplus climbing fibres—a model for activity-dependent synaptic pruning—is impaired. These findings point to deficits in synaptic plasticity and pruning as potential causes for motor problems and abnormal circuit development in autism.

Paper:

Piochon, Kloth, Grasselli, Titley, Nakayama, Hashimoto, Wan, et al.

Additional reading:

http://www.sciencedirect.com/science/article/pii/S0896627306007707

http://www.ncbi.nlm.nih.gov/pubmed/19563756

Date: 23 January 2015

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Delta-Opioid Receptors Mediate Unique Plasticity onto Parvalbumin-Expressing Interneurons in Area CA2 of the Hippocampus

Speaker: Ashley Kees (Mehta Lab)

Inhibition is critical for controlling information transfer in the brain. However, the understanding of the plasticity and particular function of different interneuron subtypes is just emerging. Using acute hippocampal slices prepared from adult mice, we report that in area CA2 of the hippocampus, a powerful inhibitory transmission is acting as a gate to prevent CA3 inputs from driving CA2 neurons. Furthermore, this inhibition is highly plastic, and undergoes a long-term depression following high-frequency, 10 Hz, or theta-burst induction protocols. We describe a novel form of long-term depression at parvalbumin-expressing (PV+) interneuron synapses that is dependent on delta-opioid receptor (DOR) activation.

Paper

Background

Date: 16 January 2015 YOUNG INVESTIGATOR SEMINAR

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Learning-Dependent Behavioral Correlates of Striatal Functional Connectivity

Speaker: Konstantin Bakhurin(Masmanidis Lab)

Because of its unique microcircuit structure, striatal activity is heavily dependent on the patterning of excitatory input the structure receives from a wide range of upstream areas. These synapses are the sites of NMDA-dependent plasticity that is thought to be important for mediating striatal-dependent forms of learning. Therefore, changes in the relationships between striatal neurons and input patterns during learning may result in a reorganization of striatal network activity. We used novel silicon-based electrophysiological probe technology to simultaneously record spiking activity from large populations of neurons in the striatum of awake, behaving mice learning a reward-guided odor-discrimination task. Using correlation-based analysis to characterize the coordinated firing of striatal neurons, we observed that during periods of rest, MSNs that preferentially encode reward-predicting odor cues were more likely to be synchronized to each other than to other, non-preferring MSNs. Furthermore, we found that the resting-state functional connectivity between reward-preferring and non-preferring MSNs was negatively correlated with animals’ performance in the task. This property was detected during early stages of learning, but was absent after extended training. These results demonstrate a learning-dependent relationship between behavioral performance and the correlated state of MSNs that fire in response to cues that predict a salient outcome.

Date: 9 January 2015 YOUNG INVESTIGATOR SEMINAR

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Pronounced impact of out of phase food intake on learning and memory

Speaker: Dawn Loh (Colwell Lab)

The circadian system is a finely tuned network of central and peripheral oscillators headed by a master pacemaker, the suprachiasmatic nucleus (SCN), which governs daily rhythms in behavior and physiology, including cognition. Disruption of the circadian system by genetic mutations or environmental manipulations has severe consequences on learning and memory. In prior work, we established the negative impact of acute jet lag on cognition, demonstrating that acute misalignment of the network of circadian oscillators has pronounced effects on long term memory.

In this study, we sought to determine the effects of chronic and stable misalignment of the circadian network by scheduling access to food at an inappropriate phase of the daily cycle, which alters the phase of many peripheral circadian oscillators without affecting the SCN. Mice were allotted a six hour window in which food was made available either during their active phase (aligned), or during their inactive phase (misaligned). Crucially, in the central nervous system, we determined that misaligned feeding alters the phase of the hippocampal circadian oscillator.

Chronic misalignment of food access resulted in reduced performance on the novel object recognition test and had a severe impact on the recall of contextual fear conditioning, indicating deficits in hippocampal-dependent learning and memory. Critically, although the temporal pattern of sleep was altered, there was no difference in the amount of sleep between the aligned and misaligned groups, thus ruling out effects of sleep deprivation on memory. At the physiological level, misaligned feeding led to deficits in hippocampal long term potentiation, suggesting circadian disruption affects synaptic plasticity.

Our findings suggest that circadian misalignment of the hippocampal oscillator has far-reaching effects on not only hippocampal physiology, but also on the functional outcome of long term memory, and highlight the importance of circadian regulation on cognition.

2014

December 2014

Date: 19 December 2014 SPECIAL SEMINAR

Time: 09:30 am

Place : Gonda 1st Floor Conference Room

Title: Fast protein-synthesis dependent memory traces require the release of stalled polysomes and are independent of translation initiation

Speaker: Wayne Sossin (McGill University)

The Integrated Center for Learning and Memory Journal Club is pleased to welcome Dr. Wayne Sossin of McGill University. All are invited.

Dr. Sossin is a world-renowned investigator of the biochemical changes that occur in the brain during learning and memory. Of particular interest to him is the identification of molecular memory traces that underlie behavioural memory. Currently, his laboratory is investigating several candidates for this molecular trace, including the activation of persistent kinases and the regulated translation of new proteins.

Date: 12 December 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: A category-free neural population supports evolving demands during decision-making

Speaker: Ben Huang

The posterior parietal cortex (PPC) receives diverse inputs and is involved in a dizzying array of behaviors. These many behaviors could rely on distinct categories of neurons specialized to represent particular variables or could rely on a single population of PPC neurons that is leveraged in different ways. To distinguish these possibilities, we evaluated rat PPC neurons recorded during multisensory decisions. Newly designed tests revealed that task parameters and temporal response features were distributed randomly across neurons, without evidence of categories. This suggests that PPC neurons constitute a dynamic network that is decoded according to the animal's present needs. To test for an additional signature of a dynamic network, we compared moments when behavioral demands differed: decision and movement. Our new state-space analysis revealed that the network explored different dimensions during decision and movement. These observations suggest that a single network of neurons can support the evolving behavioral demands of decision-making.

David Raposo, Matthew Kaufman and Anne Churchland

Date: 05 December 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Local impermeant anions establish the neuronal chloride concentration - Novel options for memory storage?

Speaker: Felix Schweizer

Neuronal intracellular chloride concentration [Cl(-)](i) is an important determinant of γ-aminobutyric acid type A (GABA(A)) receptor (GABA(A)R)-mediated inhibition and cytoplasmic volume regulation. Equilibrative cation-chloride cotransporters (CCCs) move Cl(-) across the membrane, but accumulating evidence suggests factors other than the bulk concentrations of transported ions determine [Cl(-)](i). Measurement of [Cl(-)](i) in murine brain slice preparations expressing the transgenic fluorophore Clomeleon demonstrated that cytoplasmic impermeant anions ([A](i)) and polyanionic extracellular matrix glycoproteins ([A](o)) constrain the local [Cl(-)]. CCC inhibition had modest effects on [Cl(-)](i) and neuronal volume, but substantial changes were produced by alterations of the balance between [A](i) and [A](o). Therefore, CCCs are important elements of Cl(-) homeostasis, but local impermeant anions determine the homeostatic set point for [Cl(-)], and hence, neuronal volume and the polarity of local GABA(A)R signaling.

Local Impermeant Anions Establish the Neuronal Chloride Concentration

November 2014

Date: 07 November 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: The Living Record of Memory: Genes, Neurons and Synapses

Speaker: Kelsey Martin

(This week Kelsey Martin will be presenting her SFN Presidential Special Lecture during the ICLM journal club.)

Memory requires stimulus-induced changes in gene expression, which in turn, alters synaptic connectivity and wiring in the brain. In this way, experience combines with our genome to determine who we are as individuals. This talk describes efforts to understand how experience regulates gene expression within neurons, how stimulus-induced signals are transported from distal synapses to the nucleus to alter gene expression, and how gene expression is spatially restricted to specific subcellular compartments.

October 2014

Date: 31 October 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Chronic early-life stress alters developmental and adult neurogenesis and impairs cognitive function in mice

Speaker: Viren Makhijani

Early-life stress (ES) increases vulnerability to psychopathology and impairs cognition in adulthood. These ES-induced deficits are associated with lasting changes in hippocampal plasticity. Detailed information on the neurobiological basis, the onset and progression of such changes and their sex specificity is currently lacking but is required to tailor specific intervention strategies. Here Naninck et al. use a chronic ES mouse model based on limited nesting and bedding material from postnatal day (P) 2-9 to investigate; 1) if ES leads to impairments in hippocampus-dependent cognitive function in adulthood, and 2) if these alterations are paralleled by changes in developmental and/or adult hippocampal neurogenesis. ES increased developmental neurogenesis (proliferation and differentiation) in the dentate gyrus (DG) at P9, and the number of immature (NeurD1+) cells migrating postnatally from the secondary dentate matrix, indicating prompt changes in DG structure in both sexes. ES lastingly reduced DG volume and the long-term survival of developmentally born neurons in both sexes at P150. In adult male mice only, ES reduced survival of adult-born neurons (BrdU/NeuN+ cells), while proliferation (Ki67+) and differentiation (DCX+) were unaffected. These changes correlated with impaired performance in all learning and memory tasks used here. In contrast, in female mice, despite early alterations in developmental neurogenesis, no lasting changes were present in adult neurogenesis after ES and the cognitive impairments were less prominent and only apparent in some cognitive tasks. We further show that, although neurogenesis and cognition correlate positively, only the hippocampus-dependent functions depend on changes in neurogenesis, whereas cognitive functions that are not exclusively hippocampus-dependent do not. This study indicates that chronic ES has lasting consequences on hippocampal structure and function in mice and suggests that male mice are more susceptible to ES than females. Unraveling the mechanisms that underlie the persistent ES-induced effects may have clinical implications for treatments to counteract ES-induced deficits.

Paper: Naninck et al. (2014)

Background: Oomen eta al. (2010)

Date: 24 October 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Engineering a memory with LTD and LTP

Speaker: David Glanzman

It has been proposed that memories are encoded by modification of synaptic strengths through cellular mechanisms such as long-term potentiation (LTP) and long-term depression (LTD). However, the causal link between these synaptic processes and memory has been difficult to demonstrate. Nabavi et al. present data to show that fear conditioning, a type of associative memory, can be inactivated and reactivated by LTD and LTP, respectively. This is done, first, by conditioning an animal to associate a foot shock with optogenetic stimulation of auditory inputs targeting the amygdala, a brain region known to be essential for fear conditioning. Subsequent optogenetic delivery of LTD conditioning to the auditory input inactivated memory of the shock. Then subsequent optogenetic delivery of LTP conditioning to the auditory input reactivated memory of the shock. Thus, engineered inactivation and reactivation of a memory using LTD and LTP, supports a causal link between these synaptic processes and memory.

Paper: Nabavi et al. (2014)

Background: [http://www.nature.com/news/flashes-of-light-show-how-memories-are-made-1.15330 Flashes of light show how memories are made

Date: 17 October 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Sensory-evoked LTP driven by dendritic plateau potentials in vivo

Speaker: Carlos Portera-Cailliau

Long-term synaptic potentiation (LTP) is thought to be a key process in cortical synaptic network plasticity and memory formation. Hebbian forms of LTP depend on strong postsynaptic depolarization, which in many models is generated by action potentials that propagate back from the soma into dendrites. However, local dendritic depolarization has been shown to mediate these forms of LTP as well As pyramidal cells in supragranular layers of the somatosensory cortex spike infrequently it is unclear which of the two mechanisms prevails for those cells in vivo. Using whole-cell recordings in the mouse somatosensory cortex in vivo, Gambino et al. demonstrate that rhythmic sensory whisker stimulation efficiently induces synaptic LTP in layer 2/3 (L2/3) pyramidal cells in the absence of somatic spikes. The induction of LTP depended on the occurrence of NMDAR (N-methyl-D-aspartate receptor)-mediated long-lasting depolarizations, which bear similarities to dendritic plateau potentials. In addition, they show that whisker stimuli recruit synaptic networks that originate from the posteromedial complex of the thalamus (POm). Photostimulation of channelrhodopsin-2 expressing POm neurons generated NMDAR-mediated plateau potentials, whereas the inhibition of POm activity during rhythmic whisker stimulation suppressed the generation of those potentials and prevented whisker-evoked LTP. Taken together, this data provide evidence for sensory-driven synaptic LTP in vivo, in the absence of somatic spiking. Instead, LTP is mediated by plateau potentials that are generated through the cooperative activity of lemniscal and paralemniscal synaptic circuitry.

Paper: Holtmaat_Nature_2014

Date: 10 October 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Sleep promotes branch-specific formation of dendritic spines after learning.

Speaker: Adam Frank (Silva Lab)

How sleep helps learning and memory remains unknown. Recently the Gan lab has reported in mouse motor cortex that sleep after motor learning promotes the formation of postsynaptic dendritic spines on a subset of branches of individual layer V pyramidal neurons. New spines are formed on different sets of dendritic branches in response to different learning tasks and are protected from being eliminated when multiple tasks are learned. Neurons activated during learning of a motor task are reactivated during subsequent non–rapid eye movement sleep, and disrupting this neuronal reactivation prevents branch-specific spine formation. These findings indicate that sleep has a key role in promoting learning-dependent synapse formation and maintenance on selected dendritic branches, which contribute to memory storage.

Paper: Sleep promotes branch-specific formation of dendritic spines after learning

Background Papers: Govindarajan et al (2011) Xu et al (2009)

Date: 03 October 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Volitional modulation of optically recorded calcium signals during neuroprosthetic learning

Speaker: Dean Buonomano

Brain-machine interfaces are not only promising for neurological applications, but also powerful for investigating neuronal ensemble dynamics during learning. We trained mice to operantly control an auditory cursor using spike-related calcium signals recorded with two-photon imaging in motor and somatosensory cortex. Mice rapidly learned to modulate activity in layer 2/3 neurons, evident both across and within sessions. Learning was accompanied by modifications of firing correlations in spatially localized networks at fine scales.

Paper: Volitional modulation of optically recorded calcium signals during neuroprosthetic learning

May 2014

Date: 16 May 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Olfactory cortical neurons read out a relative time code in the olfactory bulb

Speaker: Anu Goel (Buonomano Lab)

Neurons are not only sensitive to the spatial features of stimuli but are also capable of extracting temporal information from stimuli. There are several reports of temporally selective neurons in invertebrates, vertebrates as well as mammals. In particular there is evidence that neurons in the auditory system respond preferentially when pairs or sequences of tones are presented in a specific order with a certain temporal interval between them. The mechanisms underlying this temporal specificity remain to be examined in detail, but one potential candidate is the state-dependent network model. Today I will discuss evidence from a study in the rodent olfactory system where the authors show that piriform cortex neurons exhibit temporal selectivity to specific spatio-temporal stimuli delivered optogenetically to the olfactory bulb.

Paper: Olfactory cortical neurons read out a relative time code in the olfactory bulb

Date: 9 May 2014

Time: 9:30 am

Place : Gonda 2nd Floor Conference Room

Title: DNA Encoding of Learned Information

Speaker: David Glanzman

The point of these papers is that learned information is encoded as changes in DNA structure. And, further, that learned information (here, olfactory fear conditioning) can be transmitted to one's offspring. I will focus my presentation on the paper by Suberbielle et al. (2013) and bring in the paper by Dias and Ressler (2014) at the end.

Date: 2 May 2014

Time: 9:30 am

Place : Gonda 2nd Floor Conference Room

Title: Temporal structure of motor variability is dynamically regulated and predicts motor learning ability

Speaker: Alex Reeves (Otis Lab)

Individual differences in motor learning ability are widely acknowledged, yet little is known about the factors that underlie them. Here the authors explore whether movement-to-movement variability in motor output, an ubiquitous if often unwanted characteristic of motor performance, predicts motor learning ability. Surprisingly, the authors found that higher levels of task-relevant motor variability predicted faster learning both across individuals and across tasks in two different paradigms, one relying on reward-based learning to shape specific arm movement trajectories and the other relying on error-based learning to adapt movements in novel physical environments. The authors then show that training can reshape the temporal structure of motor variability, aligning it with the trained task to improve learning. These results provide experimental support for the importance of action exploration, a key idea from reinforcement learning theory, showing that motor variability facilitates motor learning in humans and that our nervous systems actively regulate it to improve learning.

Article

News and Views by Reza Shadmehr

April 2014

Date: 25 April 2014

Time: 10:00 am

Place : Gonda 1st Floor Conference Room (1357)

Title: Genetic dissection of a septohypothalamic circuit that controls stress-induced persistent anxiety

Speaker: Todd Anthony (Caltech)

This is a special seminar for a job opening in Neurobiology.

Relevant Paper: Control of Stress-Induced Persistent Anxiety by an Extra-Amygdala Septohypothalamic Circuit

Date: 18 April 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Dendritic inhibition in the hippocampus supports fear learning

Speaker: Sarah Hersman

Fear memories guide adaptive behavior in contexts associated with aversive events. The hippocampus forms a neural representation of the context that predicts aversive events. Representations of context incorporate multisensory features of the environment, but must somehow exclude sensory features of the aversive event itself. Lovett-Barron et al. investigated this selectivity using cell type-specific imaging and inactivation in hippocampal area CA1 of behaving mice. Aversive stimuli activated CA1 dendrite-targeting interneurons via cholinergic input, leading to inhibition of pyramidal cell distal dendrites receiving aversive sensory excitation from the entorhinal cortex. Inactivating dendrite-targeting interneurons during aversive stimuli increased CA1 pyramidal cell population responses and prevented fear learning. We propose subcortical activation of dendritic inhibition as a mechanism for exclusion of aversive stimuli from hippocampal contextual representations during fear learning.

Paper

Further Reading: A. Losonczy, B. V. Zemelman, A. Vaziri, J. C. Magee, Nat. Neurosci. 13, 967 – 972 (2010)

M. Lovett-Barron et al., Nat. Neurosci. 15, 423 – 430, S1 – S3 (2012)

S. Royer et al., Nat. Neurosci. 15, 769 – 775 (2012).

Date: 11 April 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Role of CCR5 in learning and memory

Speaker: Miou Zhou

This is another in the ICLM Young Investigator Lecture Series

Through a large screening of mouse strains in order to understand mechanisms responsible for long-term and remote memories, we found C-C chemokine receptor 5 (CCR5) mutant mice were one of the candidates that show enhancement in long-term and remote memories while with no changes in short-term memory. CCR5 is a G-protein coupled receptor involved in immune responses. CCR5 is also an important co-receptor which HIV uses to enter its target cells. Although CCR5 has been widely studied in immune responses and in AIDS, the role of CCR5 in plasticity and in learning and memory is not clear. Our studies show that CCR5 mutation enhances both hippocampal and cortical plasticity and results in memory enhancement, while CCR5 overexpression in excitatory neurons causes spatial memory deficits. These results suggest that CCR5 plays an important role in memories.

Date: 04 April 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Exosomes and Intercellular Signaling in the Brain

Speaker: Kelsey Martin

I'll focus on a research paper from Vivian Budnik's lab showing a role for exosomes in retrograde signaling at the fly neuromuscular junction, and provide some background from cell biological studies on the function of exosomes in transferring proteins and nucleic acids between cells. I've included a recent review from Holly Cline's lab that summarizes known functions of exosomes in neurological disease and injury, and addresses possible roles for exosomes in normal brain development and functioning.

I think this is an emerging area of cell biology that is likely to be important to the biology of learning and memory.

Budnik Paper: Regulation of Postsynaptic Retrograde Signaling by Presynaptic Exosome Release

Cline Review: Exosomes function in cell – cell communication during brain circuit development

March 2014

• • • Moved to May 16th ***

Date: 28 March 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Olfactory cortical neurons read out a relative time code in the olfactory bulb

Speaker: Anu Goel (Buonomano Lab)

Neurons are not only sensitive to the spatial features of stimuli but are also capable of extracting temporal information from stimuli. There are several reports of temporally selective neurons in invertebrates, vertebrates as well as mammals. In particular there is evidence that neurons in the auditory system respond preferentially when pairs or sequences of tones are presented in a specific order with a certain temporal interval between them. The mechanisms underlying this temporal specificity remain to be examined in detail, but one potential candidate is the state-dependent network model. Today I will discuss evidence from a study in the rodent olfactory system where the authors show that piriform cortex neurons exhibit temporal selectivity to specific spatio-temporal stimuli delivered optogenetically to the olfactory bulb.

Paper: Olfactory cortical neurons read out a relative time code in the olfactory bulb

Date: 21 March 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Behavior-driven FoxP2 regulation is necessary for songbird vocal learning

Speaker: Jon Heston (White Lab)

This is the third of this year's ICLM Junior Scientist Lecture Series.

Mutations in the transcription factor FoxP2 give rise to a specific language impairments in humans, making FoxP2 one of the few molecular toeholds into understanding the neural mechanisms underlying learned vocalization. Work by my lab and others has demonstrated that FoxP2 plays a necessary role in songbird vocal learning. My research extends these observations by using viral mediated overexpression of FoxP2 to show that behavior-driven decreases in FoxP2 levels are necessary for normal vocal learning. Moreover, I show that FoxP2 overexpression does not affect basal levels of variability but instead interferes with the ability to dynamically regulate vocal variability. Finally, I present preliminary evidence that suggests bidirectional shifts in basal ganglia output offer a plausible mechanism for these online changes in vocal variability. These results elucidate one mechanism by which FoxP2 supports vocal learning and gives insights into the potential treatment of speech and language disorders.

Here's a review that some might find helpful:

Twitter evolution: converging mechanisms in birdsong and human speech

Date: 14 March 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Variability and reproducibility in recurrent neural networks

Speaker: Rodrigo Laje (University of Quilmes, Argentina)

Rodrigo is a collaborator with Dean Buonomano.

Abstract: I'll show the experimental and theoretical work we've done during my past stay in Dean's lab, published in 2013. I'll show how our brain might use a non-ticking clock to keep time, and how this reflects in the statistics of a timing task. For this to be possible a very rich neural activity is needed, which is usually associated with lack of reproducibility. This work led us to the discovery of a new "beast": a neural network whose activity is, paradoxically, both variable and reproducible.

Date: 07 March 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Mechanisms of fear sensitization caused by acute traumatic stress: from induction to expression to potential cure

Speaker: Jennifer Perusini

This is the second of this year's ICLM Junior Scientist Lecture Series.

Abstract: Inappropriate fear regulation after severe stress is a hallmark of post-traumatic stress disorder (PTSD). We developed a model called stress-enhanced fear learning (SEFL), in which an acute footshock stressor nonassociatively and permanently enhances conditional fear learning in rats. SEFL is accompanied by several additional symptoms relevant to PTSD. We demonstrate that corticosterone acting at glucocorticoid receptors in the basolateral amygdala (BLA) is necessary to induce SEFL. Moreover, we show that corticosterone drives long-term AMPA receptor (R) subunit, glutamate receptor 1 (GluA1), expression in the BLA. Infusing an AMPAR antagonist into the BLA after the stress temporarily prevented sensitized fear expression, while specifically targeting GluA1 synthesis in the BLA using antisense oligonucleotides post-stress produced a long-lasting reversal of SEFL. These results elucidate novel neurobiological mechanisms underlying sensitized behavioral responses observed in PTSD and further indicate that a single antisense treatment directed at AMPARs within the BLA surprisingly restores normal fear responding.

A background paper can be found here:

http://www.sciencedirect.com/science/article/pii/S0149763405000606

February 2014

Date: 28 February 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Specific evidence of low-dimensional continuous attractor dynamics in grid cells

Speaker: Nick Hardy

I'll be presenting the paper "Specific evidence of low-dimensional continuous attractor dynamics in grid cells" by Yoon et al.

Abstract: We examined simultaneously recorded spikes from multiple rat grid cells, to explain mechanisms underlying their activity. Among grid cells with similar spatial periods, the population activity was confined to lie close to a two-dimensional (2D) manifold: grid cells differed only along two dimensions of their responses and otherwise were nearly identical. Relationships between cell pairs were conserved despite extensive deformations of single-neuron responses. Results from novel environments suggest such structure is not inherited from hippocampal or external sensory inputs. Across conditions, cell-cell relationships are better conserved than responses of single cells. Finally, the system is continually subject to perturbations that, were the 2D manifold not attractive, would drive the system to inhabit a different region of state space than observed. These findings have strong implications for theories of grid-cell activity and substantiate the general hypothesis that the brain computes using low-dimensional continuous attractors.

Relevant Materials:

The paper is found here

The paper doesn't present original experiments, but reanalyzes these data from these papers: http://www.pnas.org/content/109/43/17687

http://www.nature.com/neuro/journal/v10/n6/full/nn1905.html

http://www.sciencemag.org/content/312/5774/758

http://www.nature.com/nature/journal/v436/n7052/full/nature03721.html

The data from the last 2 papers can be publicly downloaded here:

http://www.ntnu.edu/kavli/research/grid-cell-data

Date: 21 February 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Dynamic Reconfiguration of Hippocampal Interneuron Circuits during Spatial Learning

Speaker: Ashley Kees

Back from studying space-time, learning, and the brain in Santa Barbara, Ashley Kees will be sharing some of her knowledge with us.

In the hippocampus, cell assemblies forming mnemonic representations of space are thought to arise as a result of changes in functional connections of pyramidal cells. We have found that CA1 interneuron circuits are also reconfigured during goal-oriented spatial learning through modification of inputs from pyramidal cells. As learning progressed, new pyramidal assemblies expressed in theta cycles alternated with previously established ones, and eventually overtook them. The firing patterns of interneurons developed a relationship to new, learning-related assemblies: some interneurons associated their activity with new pyramidal assemblies while some others dissociated from them. These firing associations were explained by changes in the weight of monosynaptic inputs received by interneurons from new pyramidal assemblies, as these predicted the associational changes. Spatial learning thus engages circuit modifications in the hippocampus that incorporate a redistribution of inhibitory activity that might assist in the segregation of competing pyramidal cell assembly patterns in space and time.

Relevant Materials:

Paper

Date: 14 February 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Basal ganglia subcircuits distinctively encode the parsing and concatenation of action sequences

Speaker: Kostya Bakhurin

This Valentine's Day, Kostya will be discussing a center of reward and desire while breaking hearts, presenting this paper from an alum of the Silva Lab.

Chunking allows the brain to efficiently organize memories and actions. Although basal ganglia circuits have been implicated in action chunking, little is known about how individual elements are concatenated into a behavioral sequence at the neural level. Using a task in which mice learned rapid action sequences, we uncovered neuronal activity encoding entire sequences as single actions in basal ganglia circuits. In addition to neurons with activity related to the start/stop activity signaling sequence parsing, we found neurons displaying inhibited or sustained activity throughout the execution of an entire sequence. This sustained activity covaried with the rate of execution of individual sequence elements, consistent with motor concatenation. Direct and indirect pathways of basal ganglia were concomitantly active during sequence initiation, but behaved differently during sequence performance, revealing a more complex functional organization of these circuits than previously postulated. These results have important implications for understanding the functional organization of basal ganglia during the learning and execution of action sequences.

Relevant Materials:

Paper

Basal Ganglia Primer

Date: 07 February 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: Distance-Dependent Scaling of AMPA Receptors: Whatever Happened To That Idea?

Speaker: Walt Babiec

The Super Bowl is over and pitchers and catchers report later this month, so I'll use a baseball metaphor. I'm pinch hitting this week due to a bunch of schedule reshuffles and no one else's interest in taking this week. Magee and Cook (2000) first reported distance-dependent scaling of AMPA receptor synapses strength in hippocampal pyramidal cells, but the origins of this scaling are not well understood. We will discuss a recent paper from the Nicoll Lab that takes on the question of whether this scaling is driven cell autonomously or as a result of extrinsic hippocampal factors.

January 2014

Date: 31 January 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: LTP requires a reserve pool of glutamate receptors independent of subunit type

Speaker: Tom O'Dell

Long-term potentiation (LTP) of synaptic transmission is thought to be an important cellular mechanism underlying memory formation. A widely accepted model posits that LTP requires the cytoplasmic carboxyl tail (C-tail) of the AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptor subunit GluA1. To find the minimum necessary requirement of the GluA1 C-tail for LTP in mouse CA1 hippocampal pyramidal neurons, Granger et al. used a single-cell molecular replacement strategy to replace all endogenous AMPA receptors with transfected subunits. In contrast to the prevailing model, they found no requirement of the GluA1 C-tail for LTP. In fact, replacement with the GluA2 subunit showed normal LTP, as did an artificially expressed kainate receptor not normally found at these synapses. The only conditions under which LTP was impaired were those with markedly decreased AMPA receptor surface expression, indicating a requirement for a reserve pool of receptors. These results suggest a fundamental change in thinking with regard to the core molecular events underlying synaptic plasticity is required.

Relevant Materials:

Paper

Welberg Commentary

Sheng, Malinow, Huganir Commentary

Date: 24 January 2014

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title: A Cholinergic Mechanism for Reward Timing within Primary Visual Cortex

Speaker: Helen Motanis (Buonomano lab)

This week I have chosen a paper entitled ‘A Cholinergic Mechanism for Reward Timing within Primary Visual Cortex’ by Chubykin et al. 2013. Neurons in rodent primary visual cortex (V1) relate operantly conditioned stimulus-reward intervals with modulated patterns of spiking output, but little is known about the locus or mechanism of this plasticity. The authors show that cholinergic basal forebrain projections to V1 are necessary for the neural acquisition, but not the expression, of reward timing in the visual cortex of awake, behaving animals. The authors also mimic reward timing in vitro by pairing white matter stimulation with muscarinic receptor activation at a fixed interval and show that this protocol results in the prolongation of electrically evoked spike train durations out to the conditioned interval. Together, these data suggest that V1 possesses the circuitry and plasticity to support reward time prediction learning and the cholinergic system serves as an important reinforcement signal, which, in vivo, conveys to the cortex the outcome of behavior.

Date: 17 January 2014

Time: 09:30 am

Place : Gonda 1st Floor Conference Room

Title: Long-term potentiation (LTP), from humble beginnings to major significance

Speaker: Terje Lømo (University of Oslo)

2013

December 2013

Date: 13 December 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title: Attention enhances synaptic efficacy and the signal-to-noise ratio in neural circuits.

Speaker: Michael Einstein (Golshani Lab)

Attention enhances the processing of salient visual stimuli. Despite thirty years of research on the correlates of attention in the visual cortex, the mechanism by which attention boosts the signal of a salient visual stimulus is still of great debate. One argument is that attention depolarizes visual cortical cells, which could increase neuronal gain by raising the probability for inputs to trigger spiking. Others say that attention synchronizes specific neural populations in such a way that their impact on downstream neurons is increased. Briggs et al. (2013) adds a new piece to the puzzle by testing how attention alters synaptic weights between the LGN and primary visual cortex in monkeys. This research suggests that attention primarily synchronizes specific neural populations as a means to increase the signal to noise ratio of attended stimuli. To conclude, I will reflect on the impact of this paper and suggest future directions for the field.

Reference: Briggs F, Mangun GR, Usrey WM (2013) Attention enhances synaptic efficacy and the signal-to-noise ratio in neural circuits. Nature 499: 476-80. http://www.nature.com/nature/journal/v499/n7459/full/nature12276.html

Date: 06 December 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title: Selection of distinct populations of dentate granule cells in response to inputs as a mechanism for pattern separation in mice.

Speaker: Denise Cai (Silva Lab)

I'd like to present this paper from the Gage/Mayford lab and discuss it in the context of the work from the Tonegawa lab (Liu et al., 2012, Ramirez et al., 2013) with their reactivation of dentate studies.

Gage/Mayford Reference: http://elife.elifesciences.org/content/2/e00312

Tonegawa References: Liu et al., 2012 Ramirez et al., 2013

November 2013

Date: 22 November 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title: Maturation of silent synapses in amygdala-accumbens projection contributes to incubation of cocaine craving

Speaker: Paul Mathews (Otis Lab)

This week I have chosen to present a paper entitled "Maturation of silent synapses in amygdala-accumbens projections contributes to incubation of cocaine craving," by Lee at al. Previous research has shown that after repeated cocaine exposure there is a rapid "silencing" of dendritic synapses in medium spiny neurons of the nucleus accumbens. These silenced synapses become rapidly (over days) un-silenced through the incorporation of Ca2+ permeable, rather than Ca2+ impermeable AMPA receptors, which normally predominate the synapse. The authors of this paper present experiments that suggest that these newly un-silenced synapses composed of Ca2+ permeable AMPA receptors underlie the cellular basis for incubated cocaine craving. Given the wide range of experimentation, from behavior to cellular physiology I think this paper should have plenty to interest most ICLM journal club participants.

Reference: http://www.nature.com/neuro/journal/v16/n11/full/nn.3533.html

Date: 15 November 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title: Spatial representations along the longitudinal hippocampal axis: Tradeoff between memory interference and generalization

Speaker: Isabel Muzzio (Dept. of Psychology, University of Pennsylvania)

The hippocampus has long been implicated in contextual gating of aversive events. Lesion and neuroanatomical studies indicate that the dorsal hippocampus specializes in spatial processing while the ventral hippocampus is more involved in emotion and anxiety. However, it is currently unclear if these regions work as independent modules processing distinct types of information or sensory and emotional inputs are integrated along the longitudinal hippocampal axis to provide a comprehensive representation of context. To investigate this question, my lab has conducted in vivo recordings from freely moving mice while animals form and retrieve contextual representations of different emotional valence in the dorsal and ventral hippocampus. We have found evidence that space is faithfully coded in both the dorsal and ventral regions in different manners. In the dorsal hippocampus, sparse finely tuned representations remap in response to the altered valence of a context forming a new stable spatial representation. Conversely, in the ventral hippocampus space is represented through population coding and emotional valence is coded through changes in firing rate. Furthermore, our data show that having a spatial representational gradient along the longitudinal axis favors a tradeoff between memory interference and generalization.

Date: 01 November 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title: Epigenetics in action: social regulation of microRNAs

Speaker: Stephanie White

My talk with discuss how the speech and language related gene, FoxP2, is regulated 'on line' during social interactions. Relevance to the LMP community is that this occurs within procedural learning circuitry in the basal ganglia. Perhaps not surprisingly, the model system in question is the songbird, especially given that lab rodents do not learn how to squeak.

Relevant Paper: "miR-9 and miR-140-5p Target FoxP2 and Are Regulated as a Function of the Social Context of Singing Behavior in Zebra Finches"

Shi Z, Luo G, Fu L, Fang Z, Wang X, Li X (2013) J Neurosci 33:16510-21.

http://www.jneurosci.org/content/33/42/16510.long

October 2013

Date: 25 October 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title: Perineuronal Nets and Plasticity

Speaker: Kelsey Martin

I will discuss a recent PNAS paper from Roger Tsien (see below) that is essentially a hypothesis paper about the function of perineuronal nets and long-term plasticity. I will also present work from other research papers on perineuronal nets during developmental and adult plasticity.

"Very long-term memories may be stored in the pattern of holes in the perineuronal net"

Tsien, RY (2013) PNAS 110:12456.

http://www.pnas.org/content/110/30/12456.full?sid=ec9e5dc0-bb51-46f5-b83c-313145c456ee

Date: 11 October 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title: Where in the Cell Is Long-Term Memory?

Speaker: David Glanzman

I will be presenting recent work from my lab.

There are no papers to read specifically for the presentation. But the following provide useful background information:

Cai, D., Pearce, K., Chen, S., and Glanzman, D. L. (2011). Protein kinase M maintains long-term sensitization and long-term facilitation in Aplysia. J. Neurosci. 31, 6421-6431. (http://www.jneurosci.org/content/31/17/6421.long)

Cai, D., Pearce, K., Chen, S., and Glanzman, David L. (2012). Reconsolidation of long-term memory in Aplysia. Curr. Biol. 22, 1783-1788. (http://www.sciencedirect.com/science/article/pii/S0960982212008639)

Date: 04 October 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title : Metabotropic NMDA Receptor Function

Speaker: Walt Babiec

Recently, two laboratories have reported data from hippocampal slice culture that the depression of AMPA receptor mediated transmission by amyloid beta is blocked by competitive NMDA receptor antagonists, e.g., APV, but not non-competitive antagonists, e.g., MK-801. One of these, the Malinow Laboratory, has proposed that NMDA receptors not only display an ionotropic function but a metabotropic function. They suggest that this metabotropic function, which requires NMDA receptor activation but not cation flux, is necessary and sufficient for generating long-term depression (LTD), which they argue mediates this amyloid beta effect. This week, we will review that data offered in support of their metabotropic NMDA hypothesis of LTD, as well as some data we have taken in the O’Dell Laboratory investigating whether such a function persists in adult animals, thus enhancing its potential for relevance to neurological disorders of aging such as Alzheimer’s Disease.

Covering This Week’s Paper: “Metabotropic NMDA receptor function is required for NMDA receptor-dependent long-term depression” PNAS (2013) 110:4027. Sadegh Nabavia, Helmut W. Kessels, Stephanie Alfonso, Jonathan Aow, Rocky Fox, and Roberto Malinow http://www.pnas.org/content/110/10/4027.long

September 2013

Date: 27 September 2013

Time: 09:30 am

Place : Gonda 2303 (2nd Floor Conference Room)

Title : The Value of Messy Neural Responses

Speaker: Dean Buonomano

Covering This Week’s Paper: “The importance of mixed selectivity in complex cognitive tasks” Nature (2013) 497:585-590. Rigotti M, Barak O, Warden MR, Wang X-J, Daw ND, Miller EK, Fusi S http://www.nature.com/nature/journal/v497/n7451/full/nature12160.html

May 2013

Date: May 10th

Time: 09:30 am

Place : Gonda 2nd Floor Conference Room

Title : Hilar Mossy Cell Degeneration Causes Transient Dentate Granule Cell Hyperexcitability and Impaired Pattern Separation

Speaker: Sarah Hersman

Although excitatory mossy cells of the hippocampal hilar region are known to project both to dentate granule cells and to interneurons, it is as yet unclear whether mossy cell activity’s net effect on granule cells is excitatory or inhibitory. To explore their influ- ence on dentate excitability and hippocampal func- tion, we generated a conditional transgenic mouse line, using the Cre/loxP system, in which diphtheria toxin receptor was selectively expressed in mossy cells. One week after injecting toxin into this line, mossy cells throughout the longitudinal axis were degenerated extensively, theta wave power of dentate local field potentials increased during exploration, and deficits occurred in contextual discrimination. By contrast, we detected no epilepti- form activity, spontaneous behavioral seizures, or mossy-fiber sprouting 5–6 weeks after mossy cell degeneration. These results indicate that the net effect of mossy cell excitation is to inhibit granule cell activity and enable dentate pattern separation.

Neuron. 2012 Dec 20;76(6):1189-200. doi: 10.1016/j.neuron.2012.10.036. Hilar mossy cell degeneration causes transient dentate granule cell hyperexcitability and impaired pattern separation. Jinde S, Zsiros V, Jiang Z, Nakao K, Pickel J, Kohno K, Belforte JE, Nakazawa K.

Front Neural Circuits. 2013;7:14. doi: 10.3389/fncir.2013.00014. Epub 2013 Feb 12. Hilar mossy cell circuitry controlling dentate granule cell excitability. Jinde S, Zsiros V, Nakazawa K.

Date: May 3rd

Time: 09:30 am

Place : Gonda ****1st Floor Conference Room****

Title : ICLM Journal Club Special Lecture

Speaker: Yiota Poirazi

The goal of this presentation is to provide a set of predictions generated by biophysical and theoretical neuron models regarding the role of dendrites in information coding across three different brain regions: the hippocampus, the prefrontal cortex and the amygdala. Towards this goal I will present modelling studies –along with supporting experimental evidence- that investigate how dendrites may be used to facilitate the coding of both spatial and temporal information at the single cell, the microcircuit and the neuronal network level. I will first discuss how the dendrites of individual CA1 pyramidal neurons may allow a single cell to discriminate between familiar versus novel memories and propagate this information to down stream cells [1]. I will then discuss how these dendritic nonlinearities may enable stimulus specificity in individual PFC pyramidal neurons during working memory [2] and underlie the emergence of sustained activity at the single cell and the microcircuit level [2,3]. Finally, I will present findings from our ongoing work in collaboration with Alcino Silva regarding the role of dendrites in shaping the formation of fear memory engrams in the amygdala.

1. Pissadaki, E.K., Sidiropoulou K., Reczko M., and Poirazi, P. “Encoding of spatio-temporal input characteristics by a single CA1 pyramidal neuron model” PLoS Comp. Biology, 2010 Dec;6(12): e1001038.

2. Sidiropoulou, K. and Poirazi, P. “Predictive features of persistent activity emergence in regular spiking and intrinsic bursting model neurons” (PLoS Comp. Biology, 2012 April; 8(4): e1002489)

3. Papoutsi, A., Sidiropoulou, K., and Poirazi, P. “PFC microcircuits as tunable and predictive modules of persistent activity.” (submitted)

April 2013

Date: April 12th

Time: 09:30 am

Place : Gonda 2303

Title : Neural mechanisms mediating inferential reasoning in rats.

Speaker: Cynthia Fast

Abstract: Many decisions are made under conditions of uncertainty. We rarely have access to all of the information in our environment that is pertinent to making an important decision. In fact, our lives are replete with ambiguous situations that nonetheless require consideration. Yet it is unclear what cognitive and neural processes enable the distinction between explicit and ambiguous situations. Moreover, it is unknown what processes mediate inferential reasoning when an ambiguous situation has been detected. We have recently discovered that rats are capable of distinguishing between the ambiguous absence of an event and its explicit absence. That is, like humans, rats appear to recognize the conditions under which they should be able to observe an event and those conditions under which the event should be hidden from observation. Interestingly, this ability depends on prior learning. In a series of experiments, we explored the necessary and sufficient features of prior learning that contribute to sensitivity to ambiguity as well as potential underlying neural mechanisms. Specifically, micro-infusions of scopolamine into the dorsal hippocampus appear to eliminate this reasoning ability, suggesting a critical role for hippocampal cholinergic modulation under normal conditions. Additionally, analysis of cfos expression in the brains of reasoning and non-reasoning rats offer further insight into possible neural circuits mediating reasoning about absent events.

Date: April 5th

Time: 09:30 am

Place : Gonda 2303

Title : "Prkcz null mice show normal learning and memory" and "PKM-ζ is not required for hippocampal synaptic plasticity, learning and memory"

Speaker: David Glanzman

Authors: Lee AM, Kanter BR, Wang D, Lim JP, Zou ME, Qiu C, McMahon T, Dadgar J, Fischbach-Weiss SC, Messing RO.

Abstract: Protein kinase M-ζ (PKM-ζ) is a constitutively active form of atypical protein kinase C that is exclusively expressed in the brain and implicated in the maintenance of long-term memory. Most studies that support a role for PKM-ζ in memory maintenance have used pharmacological PKM-ζ inhibitors such as the myristoylated zeta inhibitory peptide (ZIP) or chelerythrine. Here we use a genetic approach and target exon 9 of the Prkcz gene to generate mice that lack both protein kinase C-ζ (PKC-ζ) and PKM-ζ (Prkcz(-/-) mice). Prkcz(-/-) mice showed normal behaviour in a cage environment and in baseline tests of motor function and sensory perception, but displayed reduced anxiety-like behaviour. Notably, Prkcz(-/-) mice did not show deficits in learning or memory in tests of cued fear conditioning, novel object recognition, object location recognition, conditioned place preference for cocaine, or motor learning, when compared with wild-type littermates. ZIP injection into the nucleus accumbens reduced expression of cocaine-conditioned place preference in Prkcz(-/-) mice. In vitro, ZIP and scrambled ZIP inhibited PKM-ζ, PKC-ι and PKC-ζ with similar inhibition constant (K(i)) values. Chelerythrine was a weak inhibitor of PKM-ζ (K(i) = 76 μM). Our findings show that absence of PKM-ζ does not impair learning and memory in mice, and that ZIP can erase reward memory even when PKM-ζ is not present.

Authors: Volk LJ, Bachman JL, Johnson R, Yu Y, Huganir RL.

Abstract: Long-term potentiation (LTP), a well-characterized form of synaptic plasticity, has long been postulated as a cellular correlate of learning and memory. Although LTP can persist for long periods of time, the mechanisms underlying LTP maintenance, in the midst of ongoing protein turnover and synaptic activity, remain elusive. Sustained activation of the brain-specific protein kinase C (PKC) isoform protein kinase M-ζ (PKM-ζ) has been reported to be necessary for both LTP maintenance and long-term memory. Inhibiting PKM-ζ activity using a synthetic zeta inhibitory peptide (ZIP) based on the PKC-ζ pseudosubstrate sequence reverses established LTP in vitro and in vivo. More notably, infusion of ZIP eliminates memories for a growing list of experience-dependent behaviours, including active place avoidance, conditioned taste aversion, fear conditioning and spatial learning. However, most of the evidence supporting a role for PKM-ζ in LTP and memory relies heavily on pharmacological inhibition of PKM-ζ by ZIP. To further investigate the involvement of PKM-ζ in the maintenance of LTP and memory, we generated transgenic mice lacking PKC-ζ and PKM-ζ. We find that both conventional and conditional PKC-ζ/PKM-ζ knockout mice show normal synaptic transmission and LTP at Schaffer collateral-CA1 synapses, and have no deficits in several hippocampal-dependent learning and memory tasks. Notably, ZIP still reverses LTP in PKC-ζ/PKM-ζ knockout mice, indicating that the effects of ZIP are independent of PKM-ζ.

March 2013

Date: March 15th

Time: 09:30 am

Place : Gonda 5303 ***Note Room Change***

Title : Neural signals of extinction in the inhibitory microcircuit of the ventral midbrain

Speaker: Konstantin Bakhurin

Abstract: Midbrain dopaminergic (DA) neurons are thought to guide learning via phasic elevations of firing in response to reward predicting stimuli. The mechanism for these signals remains unclear. Using extracellular recording during associative learning, we found that inhibitory neurons in the ventral midbrain of mice responded to salient auditory stimuli with a burst of activity that occurred before the onset of the phasic response of DA neurons. This population of inhibitory neurons exhibited enhanced responses during extinction and was anticorrelated with the phasic response of simultaneously recorded DA neurons. Optogenetic stimulation revealed that this population was, in part, derived from inhibitory projection neurons of the substantia nigra that provide a robust monosynaptic inhibition of DA neurons. Thus, our results elaborate on the dynamic upstream circuits that shape the phasic activity of DA neurons and suggest that the inhibitory microcircuit of the midbrain is critical for new learning in extinction.

Date: March 8th

Time: 09:30 am

Place : Gonda 2303

Title : Long-term stabilization of place cell remapping produced by a fearful experience

Speaker: Michael Fanselow

Abstract: Fear is an emotional response to danger that is highly conserved throughout evolution because it is critical for survival. Accordingly, episodic memory for fearful locations is widely studied using contextual fear conditioning, a hippocampus-dependent task (Kim and Fanselow, 1992; Phillips and LeDoux, 1992). The hippocampus has been implicated in episodic emotional memory and is thought to integrate emotional stimuli within a spatial framework. Physiological evidence supporting the role of the hippocampus in contextual fear indicates that pyramidal cells in this region, which fire in specific locations as an animal moves through an environment, shift their preferred firing locations shortly after the presentation of an aversive stimulus (Moita et al., 2004). However, the long-term physiological mechanisms through which emotional memories are encoded by the hippocampus are unknown. Here we show that during and directly after a fearful experience, new hippocampal representations are established and persist in the long term. We recorded from the same place cells in mouse hippocampal area CA1 over several days during predator odor contextual fear conditioning and found that a subset of cells changed their preferred firing locations in response to the fearful stimulus. Furthermore, the newly formed representations of the fearful context stabilized in the long term. Our results demonstrate that place cells respond to the presence of an aversive stimulus, modify their firing patterns during emotional learning, and stabilize a long-term spatial representation in response to a fearful encounter. The persistent nature of these representations may contribute to the enduring quality of emotional memories.

Date: March 1st

Time: 09:30 am

Place : Gonda 2303

Title : Mechanisms controlling the gain of the visual cortex neurons during wakefulness

Speaker: Pierre-Olivier Polack

Abstract: Reliable acquisition and amplification of sensory input is the first essential step for learning and memory. During wakefulness the gain of sensory neurons can change with behavior. In particular, visual cortical neurons fire at higher rates to visual stimuli during locomotion than during immobility while maintaining orientation selectivity. The mechanisms underlying this change in gain are not understood. We performed whole cell recordings from layer 2/3 and layer 4 visual cortical excitatory neurons as well as from parvalbumin-positive and somatostatin-positive inhibitory neurons in mice free to rest or run on a spherical treadmill. We found that the membrane potential of all cell types became more depolarized and (with the exception of somatostatin-positive interneurons) less variable during locomotion. Cholinergic input was essential for maintaining the unimodal membrane potential distribution during immobility, while noradrenergic input was necessary for the tonic depolarization associated with locomotion. Our results provide a mechanism for how neuromodulation controls the gain and signal-to-noise ratio of visual cortical neurons during changes in the state of vigilance. We are now investigating whether the same mechanism is responsible for controlling selective attention to visual input during a perceptual learning task.

February 2013

Date: February 21st

Time: 09:30 am

Place : Gonda 2303

Title : FMRP Regulates Neurotransmitter Release and Synaptic Information Transmission by Modulating Action Potential Duration via BK Channels

Speaker: Felix Schweizer

Abstract: Loss of FMRP causes fragile X syndrome (FXS), but the physiological functions of FMRP remain highly debatable. Here we show that FMRP regulates neurotransmitter release in CA3 pyramidal neurons by modulating action potential (AP) duration. Loss of FMRP leads to excessive AP broadening during repetitive activity, enhanced presynaptic calcium influx, and elevated neurotransmitter release. The AP broadening defects caused by FMRP loss have a cell-autonomous presynaptic origin and can be acutely rescued in postnatal neurons. These presynaptic actions of FMRP are translation independent and are mediated selectively by BK channels via interaction of FMRP with BK channel’s regulatory β4 subunits. Information-theoretical analysis demonstrates that loss of these FMRP functions causes marked dysregulation of synaptic information transmission. FMRP-dependent AP broadening is not limited to the hippocampus, but also occurs in cortical pyramidal neurons. Our results thus suggest major translation-independent presynaptic functions of FMRP that may have important implications for understanding FXS neuropathology.

Date: February 1st

Time: 09:30 am

Place : Gonda 2303

Title : Experience-dependent plasticity of Network Dynamics

Speaker: Anubhuthi Goel

Abstract: Cortical computations underlying normal and abnormal brain function are not only dependent on modifications at individual synapses but on the net interaction between many forms of plasticity at the level of the entire network. Together multiple forms of plasticity govern the complex spatio-temporal patterns of activity within local networks – that is, neural dynamics. One particular learning rule that is critical in the development of functional neural dynamics in a controlled fashion is Homeostatic plasticity. We examined plasticity of network dynamics in cortical organotypic slices in response to chronic changes in activity and found that networks rely on a balance between spontaneous and evoked activity in order to drive their average activity levels towards homeostatic set points. Importantly our data highlights the fact that at the network level homeostatic mechanisms are not restricted to simple and traditional synaptic scaling phenomena wherein all the synapses are indiscriminately scaled up or down. Rather homeostatic mechanisms involve multiple forms of plasticity operating in parallel thereby allowing circuits to independently regulate spontaneous, monosynaptic, and polysynaptic activity.

Having gained some insight as to how homeostatic plasticity influences computations in general so that recurrent cortical circuits generate functional dynamic states in a stable fashion we examined one particularly interesting type of computation, namely, how does timing emerge from the plasticity of neural dynamics. Timing is fundamental to learning and behavior, and it is increasingly clear that in many cases timing is an emergent network phenomenon; but almost nothing is known about the neural mechanisms that underlie even the simplest of temporal tasks, such as discriminating a 100 and 200 ms interval. We have recently established that when cortical organotypic slices are chronically presented with specific intervals (using electrical stimulation), the network can in a sense “learn” the trained interval: after training, presentation of a single pulse results in increased neural activity around the expected time of the second pulse—as if the network “expected” the arrival of the second pulse. We view this as an example of an emergent computation in vitro because: First, the changes in the behavior of the network seem to rely on the interaction of many neurons in a circuit rather than the simple amplification of neural responses observed in traditional synaptic plasticity studies. Second, it can be said that a simple computation is taking place because the activity patterns in the trained network provide information about elapsed time. To examine the mechanisms of temporal pattern completion, we combined electrical and optical stimulation to provide “sensory spatio-temporal experience” to cortical organotypic slices. Our data suggests that the observed timing is in part due to evoked patterns of activity—neural trajectories—in which distinct points in time can be encoded by the population of active neurons. Furthermore based on our insights from homeostatic plasticity studies we believe that homeostatic mechanisms aid in the emergence and propagation of these neural trajectories in a stable manner.

January 2013

Date: January 25th

Time: 09:30 am

Place : Gonda 2303

Title : Spatial Regulation of Gene Expression in neurons During Synapse Formation and Synaptic Plasticity

Speaker: Sangmok Kim

Abstract: mRNA localization and regulated translation allow individual neurons to locally regulate the proteome of each of their myriad of subcellular compartments. To determine whether and how synaptogenic signals spatially regulate gene expression, we cultured a bifurcated Aplysia sensory neuron contacting a nontarget motor neuron, with which it did not form chemical synapses, and a target motor neuron, with which it formed glutamatergic synapses, and imaged RNA and protein localization. We find that RNAs and translational machinery are delivered throughout the neuron, but that translation is enriched at sites of synaptic contact. Investigation of the molecular mechanisms that promote local translation revealed a role for netrin-1/DCC signaling. Together, our study indicates that the spatial regulation of gene expression during synapse formation is mediated at the level of translation. This mechanism maximizes neuronal plasticity by rendering each compartment capable of locally changing its proteome in response to local cues.

2012

November

Date: November 2nd

Time: 09:30 am

Place : Gonda 2303

Title : “Memory allocation mechanisms to trap and activate emotional memories”

Speaker: Thomas Rogerson

Summary: ICLM Junior Scientist Lecture Series

Date: November 9th

Time: 09:30 am

Place : Gonda 2303

Title : “Content-Specific Fronto-Parietal Synchronization During Visual Working Memory”

Speaker: Tristan Shuman

Abstract: Lateral prefrontal and posterior parietal cortical areas exhibit task-dependent activation during working memory tasks in humans and monkeys. Neurons in these regions become synchronized during attention-demanding tasks, but the contribution of these interactions to working memory is largely unknown. Using simultaneous recordings of neural activity from multiple areas in both regions, we find widespread, task-dependent, and content-specific synchronization of activity across the fronto-parietal network during visual working memory. The patterns of synchronization are prevalent among stimulus-selective neurons and are governed by influences arising in parietal cortex. These results indicate that short-term memories are represented by large-scale patterns of synchronized activity across the fronto-parietal network.

Date: November 16th

Time: 09:30 am

Place : Gonda 2303

Title : “Hippocampal Place Fields Emerge upon Single-Cell Manipulation of Excitability During Behavior”

Speaker: Denise Cai

Abstract: The origin of the spatial receptive fields of hippocampal place cells has not been established. A hippocampal CA1 pyramidal cell receives thousands of synaptic inputs, mostly from other spatially tuned neurons; however, how the postsynaptic neuron’s cellular properties determine the response to these inputs during behavior is unknown. We discovered that, contrary to expectations from basic models of place cells and neuronal integration, a small, spatially uniform depolarization of the spatially untuned somatic membrane potential of a silent cell leads to the sudden and reversible emergence of a spatially tuned subthreshold response and place-field spiking. Such gating of inputs by postsynaptic neuronal excitability reveals a cellular mechanism for receptive field origin and may be critical for the formation of hippocampal memory representations.

Date: November 30th

Time: 09:30 am

Place : Gonda 2303

Title : “Molecular Profiling of Activated Neurons by Phosphorylated Ribosome Capture”

Speaker: Kelsey Martin

Abstract: The mammalian brain is composed of thousands of interacting neural cell types. Systematic approaches to establish the molecular identity of functional populations of neurons would advance our under- standing of neural mechanisms controlling behavior. Here, we show that ribosomal protein S6, a structural component of the ribosome, becomes phosphory- lated in neurons activated by a wide range of stimuli. We show that these phosphorylated ribosomes can be captured from mouse brain homogenates, thereby enriching directly for the mRNAs expressed in discrete subpopulations of activated cells. We use this approach to identify neurons in the hypo- thalamus regulated by changes in salt balance or food availability. We show that galanin neurons are activated by fasting and that prodynorphin neu- rons restrain food intake during scheduled feed- ing. These studies identify elements of the neural circuit that controls food intake and illustrate how the activity-dependent capture of cell-type-specific transcripts can elucidate the functional organization of a complex tissue.

October

Date: October 26th

Time: 09:30 am

Place : Gonda 2303

Title : “Why are there so many types of inhibitory neurons”

Speaker: Dr. Dean Buonomano

Related Material:

Division and subtraction by distinct cortical inhibitory networks in vivo

Nathan R. Wilson1*, Caroline A. Runyan1*, Forea L. Wang1 & Mriganka Sur1

Brain circuits process information through specialized neuronal subclasses interacting within a network. Revealing their interplay requires activating specific cells while monitoring others in a functioning circuit. Here we use a new platform for two-way light-based circuit interrogation in visual cortex in vivo to show the computational implications of modulating different subclasses of inhibitory neurons during sensory processing. We find that soma-targeting, parvalbumin-expressing (PV) neurons principally divide responses but preserve stimulus selectivity, whereas dendrite-targeting, somatostatin-expressing (SOM) neurons principally subtract from excitatory responses and sharpen selectivity. Visualized in vivo cell-attached recordings show that division by PV neurons alters response gain, whereas subtraction by SOM neurons shifts response levels. Finally, stimulating identified neurons while scanning many target cells reveals that single PV and SOM neurons functionally impact only specific subsets of neurons in their projection fields. These findings provide direct evidence that inhibitory neuronal subclasses have distinct and complementary roles in cortical computations.

Date: October 5th

Time: 09:30 am

Place : Gonda 2303

Title : “Dissecting spatial knowledge from spatial choice by hippocampal NMDA receptor deletion”

Speaker: Dr. Tom O'Dell

Summary:

Hippocampal NMDA receptors (NMDARs) and NMDAR-dependent synaptic plasticity are widely considered crucial substrates of long-term spatial memory, although their precise role remains uncertain. Here we show that Grin1∆DGCA1 mice, lacking GluN1 and hence NMDARs in all dentate gyrus and dorsal CA1 principal cells, acquired the spatial reference memory water maze task as well as controls, despite impairments on the spatial reference memory radial maze task. When we ran a spatial discrimination water maze task using two visually identical beacons, Grin1∆DGCA1 mice were impaired at using spatial information to inhibit selecting the decoy beacon, despite knowing the platform’s actual spatial location. This failure could suffice to impair radial maze performance despite spatial memory itself being normal. Thus, these hippocampal NMDARs are not essential for encoding or storing long-term, associative spatial memories. Instead, we demonstrate an important function of the hippocampus in using spatial knowledge to select between alternative responses that arise from competing or overlapping memories.

August

Date: August 17th

Time: 09:30 am

Place : ***53-105, CHS.***

Title : “Calpain: a key component of synaptic plasticity and learning & memory?”

Speaker: Dr. Michel Baudry

Summary:

In 1984, Gary Lynch and Michel Baudry proposed the hypothesis that the calcium-dependent protease, calpain, plays an important role in LTP and in learning and memory. Dr. Baudry will review the evidence accumulated over the last 2 years that argues the importance of calpain in synaptic plasticity and identifies critical targets for calpain, thus supporting its role in regulating structural organization and function of synaptic contacts.

May

Date: May 4th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Generation of a synthetic memory trace"

Speaker: Don Julien

Summary:

We investigated the effect of activating a competing, artificially generated, neural representation on encoding of contextual fear memory in mice. We used a c-fos?based transgenic approach to introduce the hM3Dq DREADD receptor (designer receptor exclusively activated by designer drug) into neurons naturally activated by sensory experience. Neural activity could then be specifically and inducibly increased in the hM3Dq-expressing neurons by an exogenous ligand. When an ensemble of neurons for one context (ctxA) was artificially activated during conditioning in a distinct second context (ctxB), mice formed a hybrid memory representation. Reactivation of the artificially stimulated network within the conditioning context was required for retrieval of the memory, and the memory was specific for the spatial pattern of neurons artificially activated during learning. Similar stimulation impaired recall when not part of the initial conditioning.

Relevant Reading Material:

Science. 2012 Mar 23;335(6075):1513-6. Generation of a synthetic memory trace. Garner AR, Rowland DC, Hwang SY, Baumgaertel K, Roth BL, Kentros C, Mayford M.

Date: May 11th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Conditional modulation of spike-timing- dependent plasticity for olfactory learning"

Speaker: David Glanzman

Summary:

Mushroom bodies are a well-known site for associative learning in insects. Yet the precise mechanisms that underlie plasticity there and ensure their specificity remain elusive. In locusts, the synapses between the intrinsic mushroom body neurons and their postsynaptic targets obey a Hebbian spike-timing-dependent plasticity (STDP) rule. Although this property homeostatically regulates the timing of mushroom body output, its potential role in associative learning is unknown. Here we show in vivo that pre-post pairing causing STDP can, when followed by the local delivery of a reinforcement-mediating neuromodulator, specify the synapses that will undergo an associative change. At these synapses, and there only, the change is a transformation of the STDP rule itself. These results illustrate the multiple actions of STDP, including a role in associative learning, despite potential temporal dissociation between the pairings that specify synaptic modification and the delivery of reinforcement-mediating neuromodulator signals.

Relevant Reading Material:

Nature. 2012 Jan 25;482(7383):47-52. doi: 10.1038/nature10776. Conditional modulation of spike-timing-dependent plasticity for olfactory learning. Cassenaer S, Laurent G.

Date: May 18th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Corticostriatal plasticity is necessary for learning intentional neuroprosthetic skills"

Speaker: Lisa Moore

Summary:

The ability to learn new skills and perfect them with practice applies not only to physical skills but also to abstract skills, like motor planning or neuroprosthetic actions. Although plasticity in corticostriatal circuits has been implicated in learning physical skills, it remains unclear if similar circuits or processes are required for abstract skill learning. Here we use a novel behavioural task in rodents to investigate the role of corticostriatal plasticity in abstract skill learning. Rodents learned to control the pitch of an auditory cursor to reach one of two targets by modulating activity in primary motor cortex irrespective of physical movement. Degradation of the relation between action and outcome, as well as sensory-specific devaluation and omission tests, demonstrate that these learned neuroprosthetic actions are intentional and goal-directed, rather than habitual. Striatal neurons change their activity with learning, with more neurons modulating their activity in relation to target-reaching as learning progresses. Concomitantly, strong relations between the activity of neurons in motor cortex and the striatum emerge. Specific deletion of striatal NMDA receptors impairs the development of this corticostriatal plasticity, and disrupts the ability to learn neuroprosthetic skills. These results suggest that corticostriatal plasticity is necessary for abstract skill learning, and that neuroprosthetic movements capitalize on the neural circuitry involved in natural motor learning.Relevant Reading Material:

Nature. 2012 Mar 4;483(7389):331-5. doi: 10.1038/nature10845. Corticostriatal plasticity is necessary for learning intentional neuroprosthetic skills.

April

Date: Apr 20th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Optogenetic stimulation of a hippocampal engram activates fear memory recall"

Speaker: Alexander Reeves

Summary:

A specific memory is thought to be encoded by a sparse population of neurons. These neurons can be tagged during learning for subsequent identification and manipulation. Moreover, their ablation or inactivation results in reduced memory expression, suggesting their necessity in mnemonic processes. However, the question of sufficiency remains: it is unclear whether it is possible to elicit the behavioural output of a specific memory by directly activating a population of neurons that was active during learning. Here the authors show in mice that optogenetic reactivation of hippocampal neurons activated during fear conditioning is sufficient to induce freezing behavior. The authors labelled a population of hippocampal dentate gyrus neurons activated during fear learning with ChR2 and later optically reactivated these neurons in a different context. The mice showed increased freezing only upon light stimulation, indicating light-induced fear memory recall. This freezing was not detected in non-fear-conditioned mice expressing ChR2 in a similar proportion of cells, nor in fear-conditioned mice with cells labelled by eYFP instead of ChR2. Finally, activation of cells labelled in a context not associated with fear did not evoke freezing in mice that were previously fear conditioned in a different context, suggesting that light-induced fear memory recall is context specific. Together, their findings indicate that activating a sparse but specific ensemble of hippocampal neurons that contribute to a memory engram is sufficient for the recall of that memory. Moreover, their experimental approach offers a general method of mapping cellular populations bearing memory engrams.

Relevant Reading Material:

Optogenetic stimulation of a hippocampal engram activates fear memory recall. Liu X, Ramirez S, Pang PT, Puryear CB, Govindarajan A, Deisseroth K, Tonegawa S. Nature. 2012 Mar 22. doi: 10.1038/nature11028. [Epub ahead of print]

Date: Apr 13th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Activity Recall in a Visual Cortical Ensemble"

Speaker: Weixiang Chen

Summary:

Cue-triggered recall of learned temporal sequences is an important cognitive function that has been attributed to higher brain areas. Here recordings in both anesthetized and awake rats demonstrate that after repeated stimulation with a moving spot that evoked sequential firing of an ensemble of primary visual cortex (V1) neurons, just a brief flash at the starting point of the motion path was sufficient to evoke a sequential firing pattern that reproduced the activation order evoked by the moving spot. The speed of recalled spike sequences may reflect the internal dynamics of the network rather than the motion speed. In awake rats, such recall was observed during a synchronized ('quiet wakeful') brain state having large-amplitude, low-frequency local field potential (LFP) but not in a desynchronized ('active') state having low-amplitude, high-frequency LFP. Such conditioning-enhanced, cue-evoked sequential spiking of a V1 ensemble may contribute to experience-based perceptual inference in a brain state?dependent manner.

Relevant Reading Material:

Nat Neurosci. 2012 Jan 22;15(3):449-55, S1-2. doi: 10.1038/nn.3036. Activity recall in a visual cortical ensemble. Xu S, Jiang W, Poo MM, Dan Y.

Date: Apr 6th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Dynamics of Retrieval Strategies for Remote Memories"

Speaker: Thomas Rogerson

Summary:

Prevailing theory suggests that long-term memories are encoded via a two-phase process requiring early involvement of the hippocampus followed by the neocortex. Contextual fear memories in rodents rely on the hippocampus immediately following training but are unaffected by hippocampal lesions or pharmacological inhibition weeks later. With fast optogenetic methods, we examine the real-time contribution of hippocampal CA1 excitatory neurons to remote memory and find that contextual fear memory recall, even weeks after training, can be reversibly abolished by temporally precise optoge- netic inhibition of CA1. When this inhibition is extended to match the typical time course of phar- macological inhibition, remote hippocampus depen- dence converts to hippocampus independence, suggesting that long-term memory retrieval normally depends on the hippocampus but can adaptively shift to alternate structures. Further revealing the plasticity of mechanisms required for memory recall, we confirm the remote-timescale importance of the anterior cingulate cortex (ACC) and implicate CA1 in ACC recruitment for remote recall.

Relevant Reading Material:

Cell. 2011 Oct 28;147(3):678-89. Epub 2011 Oct 20. Dynamics of retrieval strategies for remote memories. Goshen I, Brodsky M, Prakash R, Wallace J, Gradinaru V, Ramakrishnan C, Deisseroth K.

March

Date: Mar 9th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Triggering and degrading associative memory formation"

Speaker: Joshua Johansen PhD

Summary:

Aversive experiences powerfully regulate memory formation by activating ‘teaching signal’ circuits in the brain which can engage neural plasticity in memory storage areas resulting in associative memories. Fear conditioning is a useful paradigm in which to examine the mechanisms by which aversive experiences trigger associative memories because a site of neural plasticity mediating the learning has been identified in the lateral nucleus of the amygdala. Aversive stimuli can either engage or degrade memory formation depending on the temporal placement of aversive stimuli in relation to sensory cues in the environment. Using a combination of optogenetic, electrophysiological and behavioral approaches I examined the neural mechanisms in the lateral amygdala by which aversive experiences trigger or degrade behavioral fear memory formation and neural plasticity. The results of these experiments suggest that combined Hebbian and neuromodulatory mechanisms trigger behavioral fear learning and neural plasticity in the lateral amygdala. In addition, activation of LA pyramidal neurons by aversive stimuli serves as a switch to either induce or degrade fear memory formation depending on the temporal placement of the aversive stimuli during learning.

Date: Mar 2nd

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Heterogeneous reallocation of presynaptic efficacy in recurrent excitatory circuits adapting to inactivity."

Speaker: Anubhuthi Goel, Ph.D.

Homeostatic plasticity is an important negative feedback regulator that maintains stability within networks of neurons. The synaptic basis and mechanisms underlying homeostatic plasticity have been extensively studied, however a large number of these investigations are restricted to understanding homeostatic modifications at feed forward pathways. This paper provides compelling evidence that the rules under which homeostatic plasticity operates are very different for recurrently connected networks and that traditional homogenous homeostatic adaptation is not enforced across all synapses.

Relevant Reading Material:

Nat Neurosci. 2011 Dec 18;15(2):250-7. doi: 10.1038/nn.3004. Heterogeneous reallocation of presynaptic efficacy in recurrent excitatory circuits adapting to inactivity. Mitra A, Mitra SS, Tsien RW.

February

Date: Feb 24th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Inducible and Selective Erasure of Memories in the Mouse Brain via Chemical-Genetic Manipulation"

Speaker: Adam Frank.

Summary:

I will present Joe Tsien's 2008 Neuron paper about a chemical-genetic approach to study CaMKIIa function ("Inducible and Selective Erasure of Memories in the Mouse Brain via Chemical-Genetic Manipulation"). This paper is a continuation of work beginning in 2003, when his lab generated a CaMKIIa overexpressing mouse with a targeted mutation in CaMKIIa that makes it highly susceptible to inhibition by a modified kinase inhibitor (Wang, 2003, PNAS). This story of overexpression and inhibition of wildtype CaMKIIa activity is interesting and provocative and raises as many questions as it answers. I am particularly interested in these results as I have generated a BAC transgenic mouse that overexpresses the same CaMKIIa mutation as that generated in the Tsien lab. I am hopeful we can have a lively discussion about his results and the important questions they raise. Relevant Reading Material:

Neuron. 2008 Oct 23;60(2):353-66. Inducible and selective erasure of memories in the mouse brain via chemical-genetic manipulation. Cao X, Wang H, Mei B, An S, Yin L, Wang LP, Tsien JZ.

Proc Natl Acad Sci U S A. 2003 Apr 1;100(7):4287-92. Epub 2003 Mar 19. Inducible protein knockout reveals temporal requirement of CaMKII reactivation for memory consolidation in the brain. Wang H, Shimizu E, Tang YP, Cho M, Kyin M, Zuo W, Robinson DA, Alaimo PJ, Zhang C, Morimoto H, Zhuo M, Feng R, Shokat KM, Tsien JZ.

January

Date: Jan 6th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Practice makes perfect: defining the role of inhibition in vision and sensory learning."

Speaker: Sandra Kuhlman, Ph.D.

GABAergic inhibition is a key mediator of experience-dependent plasticity during postnatal development, and accumulating evidence identifies aberrant GABAergic function in schizophrenia and autism. However, the mechanisms by which inhibition regulates plasticity and learning in-vivo are largely unknown, and by extension it is not well understood how disturbance of cellular signaling pathways within inhibitory interneurons impacts cortical function in-vivo. Using in-vivo targeted electrophysiological recording of an identified inhibitory interneuron cell type, the parvalbumin (PV+) fast-spiking GABAergic interneuron, we found that visual experience uniquely broadens orientation tuning of PV+ interneurons at a time during development when excitatory neurons become more sharply tuned (Kuhlman et al., Nature Neuroscience 2011). Furthermore, we found that inhibitory broadening precedes binocular matching of excitatory orientation tuning, thus establishing that maturation of the recruitment of inhibition is a candidate for initiating binocular plasticity of excitatory neurons during the critical period. These results highlight the need for designing treatment strategies to rescue recruitment of PV+ interneurons in disease, thereby expanding the existing focus which is to enhance GABAergic synaptic output.

Perceptual learning is a progressive process of skill acquisition in which neural response properties are re-shaped by experience, even at the earliest stages of sensory processing. Thus, the very perception of the environment which informs motor output and behavioral action is itself modified during learning. How does recruitment of inhibition regulate sensory learning? Using techniques described above in combination with recent advances in head-fixed mouse behavior, this is now a tractable question in mice. I will outline a strategy to define the unique roles of specific inhibitory interneuron subclasses during ‘practice’, a.k.a. progressive learning.

Date: Jan 13th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Inhibitory Plasticity"

Speaker: Dean Buonomano, Ph.D.

Releavant Reading Material:

Vogels TP, Sprekeler H, Zenke F, Clopath C, Gerstner W (2011) Science 334:1569-1573. Inhibitory Plasticity Balances Excitation and Inhibition in Sensory Pathways and Memory Networks http://www.sciencemag.org/content/334/6062/1569.abstract

Froemke RC, Merzenich MM, Schreiner CE (2007) Nature 450:425-429. A synaptic memory trace for cortical receptive field plasticity. http://www.nature.com/nature/journal/v450/n7168/full/nature06289.html

Date: Jan 20th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "A disinhibitory microcircuit for associative fear learning in the auditory cortex"

Speaker: Walter Babiec, Ph.D.

Summary: Learning causes a change in how information is processed by neuronal circuits. Whereas synaptic plasticity, an important cellular mechanism, has been studied in great detail, we know much less about how learning is implemented at the level of neuronal circuits and, in particular, how interactions between distinct types of neurons within local networks contribute to the process of learning. Here we show that acquisition of associative fear memories depends on the recruitment of a disinhibitory microcircuit in the mouse auditory cortex. Fear-conditioning-associated disinhibition in auditory cortex is driven by foot-shock-mediated cholinergic activation of layer 1 interneurons, in turn generating inhibition of layer 2/3 parvalbumin-positive interneurons. Importantly, pharmacological or optogenetic block of pyramidal neuron disinhibition abolishes fear learning. Together, these data demonstrate that stimulus convergence in the auditory cortex is necessary for associative fear learning to complex tones, define the circuit elements mediating this convergence and suggest that layer-1-mediated disinhibition is an important mechanism underlying learning and information processing in neocortical circuits.

Releavant Reading Material: Johannes J. Letzkus1*, Steffen B. E. Wolff1,2*, Elisabeth M. M. Meyer1,2, Philip Tovote1, Julien Courtin3, Cyril Herry3 & Andreas Lu ̈thi1 (2011) Nature 480:331-335. A disinhibitory microcircuit for associative fear learning in the auditory cortex http://www.nature.com/nature/journal/v480/n7377/full/nature10674.html

2011

February

Feb 25th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title :A selective role for dopamine in stimulus–reward learning

Speaker: Michael Faneslow

Summary: Flagel et al Nature 469, 53–57 (06 January 2011)

Relevant Information:

Paper

Supp

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March

Mar 4th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : Maladaptive Cortical Plasticity and Plasticity

Speaker: Dean Buonomano

Summary: Engineer ND, Riley JR, Seale JD, Vrana WA, Shetake JA, Sudanagunta SP, Borland MS, Kilgard MP (2011) Nature 470:101-104. Reversing pathological neural activity using targeted plasticity

Relevant Information:

Paper

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Mar 11th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : Memory enhancement and PKM Zeta

Speaker: Yong-Seok Lee

Summary: Yong-Seok Lee will present the newest paper from the Dudai Lab regarding overexpression of PKM in the neocortex and its enhancement of LTM.

Relevant Information:

Paper

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Mar 18th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : Notch Signaling

Speaker: Kelsey Martin

Summary: Notch signaling plays critical roles during the development of the nervous system. Several studies have suggested that Notch signaling in neurons is also involved in learning and memory and synaptic plasticity in the mature brain. However, these studies have been suggestive rather than conclusive. Moreover, studies from Ben Barres indicate that Notch receptor and ligands are expressed at very low levels in mature neurons, and at very high levels in glia. I will present a paper from Nick Gaiano's lab that argues that Notch signals from synapse to nucleus in mature hippocampal neurons and that this signaling is required for long-term potentiation and memory acquisition. Gaiano's data further indicates that the immediate early gene arc regulates Notch signaling in neurons.

The reference for the primary paper is:

Activity-induced notch signaling in neurons requires arc/arg3.1 and is essential for synaptic plasticity in hippocampal networks.

Relevant Information:

Paper

Review

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April

01st Apr

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : A critical role for IGF-II in memory consolidation and enhancement

Speaker: Ravi Ponnusamy

Summary: not provided

Relevant Information:

Paper

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08th Apr

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : The dendritic branch is the preferred integrative unit for protein synthesis-dependent LTP.

Speaker: Walter Babiec

Summary: The late-phase of long-term potentiation (L-LTP), the cellular correlate of long-term memory, induced at some synapses facilitates L-LTP expression at other synapses receiving stimulation too weak to induce L-LTP by itself. Using glutamate uncaging and two-photon imaging, we demonstrate that the efficacy of this facilitation decreases with increasing time between stimulations, increasing distance between stimulated spines and with the spines being on different dendritic branches. Paradoxically, stimulated spines compete for L-LTP expression if stimulated too closely together in time. Furthermore, the facilitation is temporally bidirectional but asymmetric. Additionally, L-LTP formation is itself biased toward occurring on spines within a branch. These data support the Clustered Plasticity Hypothesis, which states that such spatial and temporal limits lead to stable engram formation, preferentially at synapses clustered within dendritic branches rather than dispersed throughout the dendritic arbor. Thus, dendritic branches rather than individual synapses are the primary functional units for long-term memory storage

Relevant Information:

Paper

Supp

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Apr 15th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : Mushroom Body Output Neurons Encode Odor-Reward Associations

Speaker: David Glanzman

Summary: The paper describes neural correlates of odor representation and olfactory reward learning in honeybees using both population and single unit recording from the mushroom bodies.

Relevant Information: Paper

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Apr 22nd

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title :From Drosophila olfaction to a general circuit model for behavioral habituation.

Speaker: Mani Ramaswami

Summary:

Relevant Information:

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Date: Apr 27th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title :The role of Thorase in the surface expression of glutamate receptors and its implications for synaptic plasticity and behavior

Speaker: Adam Roberts

Summary: Zhang et al., 2011 indicate that the AAA+ ATPase Thorase is required for the internalization of AMPARs by dissociating the GRIP1-GluR2 interaction. Genetic manipulation of Thorase expression modifies the surface expression of GluR1 and GluR2 in an ATP-dependent manner. Thorase KO mice have enhanced LTP, deficits in LTD, and larger AMPAR-dependent currents. These alterations in nervous system function result in deficits in learning and memory.

Relevant Information:

Paper

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May

Date: May 13th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title :The role of Thorase in the surface expression of glutamate receptors and its implications for synaptic plasticity and behavior

Speaker: Adam Roberts

Summary: Zhang et al., 2011 indicate that the AAA+ ATPase Thorase is required for the internalization of AMPARs by dissociating the GRIP1-GluR2 interaction. Genetic manipulation of Thorase expression modifies the surface expression of GluR1 and GluR2 in an ATP-dependent manner. Thorase KO mice have enhanced LTP, deficits in LTD, and larger AMPAR-dependent currents. These alterations in nervous system function result in deficits in learning and memory.

Relevant Information:

Paper

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Date: May 17th

Time 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title: Action-Potential Modulation During Axonal Conduction

Speaker: Besim Ugzil"

Summary: Once initiated near the soma, an action potential (AP) is thought to propagate autoregeneratively and distribute uniformly over axonal arbors. We challenge this classic view by showing that APs are subject to waveform modulation while they travel down axons. Using fluorescent patch-clamp pipettes, we recorded APs from axon branches of hippocampal CA3 pyramidal neurons ex vivo. The waveforms of axonal APs increased in width in response to the local application of glutamate and an adenosine A1 receptor antagonist to the axon shafts, but not to other unrelated axon branches. Uncaging of calcium in periaxonal astrocytes caused AP broadening through ionotropic glutamate receptor activation. The broadened APs triggered larger calcium elevations in presynaptic boutons and facilitated synaptic transmission to postsynaptic neurons. This local AP modification may enable axonal computation through the geometry of axon wiring.

Releavant Information:

Paper

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Date: May 17th

Time 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title: Action-Potential Modulation During Axonal Conduction

Speaker: Besim Ugzil"

Summary: Once initiated near the soma, an action potential (AP) is thought to propagate autoregeneratively and distribute uniformly over axonal arbors. We challenge this classic view by showing that APs are subject to waveform modulation while they travel down axons. Using fluorescent patch-clamp pipettes, we recorded APs from axon branches of hippocampal CA3 pyramidal neurons ex vivo. The waveforms of axonal APs increased in width in response to the local application of glutamate and an adenosine A1 receptor antagonist to the axon shafts, but not to other unrelated axon branches. Uncaging of calcium in periaxonal astrocytes caused AP broadening through ionotropic glutamate receptor activation. The broadened APs triggered larger calcium elevations in presynaptic boutons and facilitated synaptic transmission to postsynaptic neurons. This local AP modification may enable axonal computation through the geometry of axon wiring.

Relevant Information:

Paper

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Date: May 27th

Time 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title: "What makes a place cell?"

Speaker: Justin Shobe"

Summary: Once initiated near the soma, an action potential (AP) is thought to propagate autoregeneratively and distribute uniformly over axonal arbors. We challenge this classic view by showing that APs are subject to waveform modulation while they travel down axons. Using fluorescent patch-clamp pipettes, we recorded APs from axon branches of hippocampal CA3 pyramidal neurons ex vivo. The waveforms of axonal APs increased in width in response to the local application of glutamate and an adenosine A1 receptor antagonist to the axon shafts, but not to other unrelated axon branches. Uncaging of calcium in periaxonal astrocytes caused AP broadening through ionotropic glutamate receptor activation. The broadened APs triggered larger calcium elevations in presynaptic boutons and facilitated synaptic transmission to postsynaptic neurons. This local AP modification may enable axonal computation through the geometry of axon wiring.

Releavant Information: Paper

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June

Date: Jun 17th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Insulin Signaling and Dietary Restriction Differentially Influence the Decline of Learning and Memory with Age"

Speaker: Kelsey Martin

Summary: This paper from Coleen Murphy's lab at Princeton describes a novel assay for short and long-term associative memory in the worm c. elegans. Using this assay, the authors show that long-term memory declines very early in c elegans, before any deficits in chemotaxis or motility. Analysis of genetic mutants identifies a specific role for CREB during long-term memory, and further reveals that long-term memory is differentially regulated by the insulin/IGF-1 and dietary restriction longevity pathways.

Relevant Information:

Paper

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July

Date: Jul 08th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "The Origin of Time (in the Songbird Motor Pathway)"

Speaker: Michael A. Long

Summary: Not Provided

Relevant Information:

Lab Homepage

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Date: Jul 22nd

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : ""Maps for navigating published work and informing experiment planning""

Speaker: Alcino J Silva and Anthony Landreth

Summary: The increasing volume and complexity of published studies in neuroscience have made it difficult to determine what is known, what is uncertain, and how to contribute effectively to one’s field. Therefore, there is a pressing need for strategies to derive simplified useful representations (i.e. maps) of previous findings and to help experiment planning. Toward these goals, we introduce a framework for classifying experiments and an approach for integrating experimental results based on implicit and explicit research practices in molecular and cellular studies of cognitive function. The development and explicit use of approaches like this one will enable researchers to systematically identify convergent evidence critical for assembling maps of published information. These maps will not only provide succinct summaries of published information, they will also be invaluable during experiment planning.

Relevant Information:

Internally circulated PDF (check your LMP email)

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Date: Jul 29th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : ""A neural prosthesis for memory? ""

Speaker: Dean Buonomano

Summary: A discussion on the following paper:

A cortical neural prosthesis for restoring and enhancing memory.

Berger TW, Hampson RE, Song D, Goonawardena A, Marmarelis VZ, Deadwyler SA, Journal of Neural Engineering 8:046017 (2011).

Relevant Information:

http://iopscience.iop.org/1741-2552/8/4/046017/pdf/1741-2552_8_4_046017.pdf

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August

Date: Aug 05th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : ""Intact Performance on Feature-Ambiguous Discriminations in Rats with Lesions of the Perirhinal Cortex ""

Speaker: Walter Babiec

Summary: clark et al., have developed a behavioral paradigm for the rat that makes it possible to separate the evaluation of memory functions from the evaluation of perceptual functions. Animals were given extensive training on an automated two-choice discrimination task and then maintained their memory performance at a high level while interpolated probe trials tested visual perceptual ability. The probe trials systematically varied the degree of feature ambiguity between the stimuli. As feature ambiguity increased, performance declined in an orderly, monotonic manner. Bilateral lesions of the perirhinal cortex fully spared the capacity to make feature-ambiguous discriminations and the performance of lesioned and intact animals was indistinguishable at every difficulty level. In contrast, the perirhinal lesions did impair recognition memory. The findings suggest that the perirhinal cortex is important for memory and not for perceptual functions.

Relevant Information:

http://www.cell.com/neuron/abstract/S0896-6273(11)00197-8?switch=standard

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Date : Aug 12th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : " Mushroom body efferent neurons responsible for aversive olfactory memory retrieval in Drosophila "

Speaker: David Glanzman

Summary: In this paper Preat and colleagues identify specific neurons in the fly's brain that are essential for the retrieval of a conditioned olfactory memory. These neurons (MB-V2) are found in the mushroom bodies of the Drosophila brain, an area previously identified as critical for olfactory conditioning, during which flies learn to avoid an odor that is paired with shock. Interestingly, the MB-V2 neurons, although essential for the retrieval of both short-term and long-lasting memory, are not required for either memory formation or memory consolidation. The authors propose that MB-V2 neurons recruit the olfactory pathway involved in innate odor avoidance during memory retrieval.

Relevant Information:

Nat. Neurosci. (2011) vol. 14 (7) pp. 903-10

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Date: Aug 19th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : " Drosophila mutants undercover functional specificity in mushroom body architecture and a novel role for Importin- (alpha)2 in mushroom body development and classical conditioning "

Speaker: Christine Serway

Summary: The interplay between brain anatomy, neural network organization and behavior has been well studied in Drosophila for over three decades. The first experimental evidence implicating the mushroom bodies (MBs) as centers of sensory integration and association in flies came from anatomical and behavioral work on brain structure mutants. Here we present a detailed analysis of three genes using mutant alleles initially described by Martin Heisenberg et al. more than 25 years ago. We characterized the different levels of associative conditioning and mushroom body defects seen in mushroom body miniature B (mbmB), small mushroom bodies (smu) and mushroom bodies reduced (mbr). This work has allowed us to implicate subsets of the MBs in different forms of associative conditioning. Surprisingly most of the mutants created in this screen have yet to be molecularly characterized. Extensive complementation analysis and sequencing revealed mbmB to be synonymous with the Drosophila Importin-2 (Imp-2). We present rescue experiments, western blot analysis, and have demonstrated that all Imp-2 domains are required for normal MB development. In Drosophila, imp-2 mediated nuclear transport is necessary for proper axon guidance, neuronal injury response, synaptic plasticity, cell proliferation and apoptosis, while its role in central brain development has not been investigated until now. This work provides a novel link between Importin--2 and MB development and offers insight on the cell biology of developmental and behavioral plasticity.

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September

Date: Sep 02nd

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : ""Prior experience modulates a natural threshold for memory formation ""

Speaker: Kiriana Cowansage

Summary: Our current understanding of the molecular requirements for long–term memory come largely from studies that use experimental manipulations to alter average behavior. Few studies, on the other hand, have investigated the contribution of plasticity-related proteins, like CREB, to existing behavioral differences in memory strength that emerge naturally from genetically diverse populations. In this talk I will begin by presenting work from the labs of Joe LeDoux and Eric Klann (in collaboration with Sheena Josselyn) to identify rats from a normally distributed group that fail to form typical cued fear associations and express reduced baseline levels of phospho-CREB. Memory in this subset of rats was selectively improved by both pre-training exposure to contextual novelty and by virally mediated enhancement of amygdala CREB activity. These results provide some conceptual basis for current plans to investigate the cellular dynamics of weak versus strong associative memory traces in the lab of Mark Mayford, using a novel genetically encoded fluorescent timer expressed in mice under the control of neural activity.

Relevant Information:

Subach et al (2009) Nat. Chem Biol

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Date: Sep 23rd

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : " 2½ Short Stories of Pavlov's Flies "

Speaker: Steven de Belle

Summary: Not provided

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Date: Sep 30th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : " Talk 1: Grid cells, theta oscillations, and a novel code phase code of the head direction signal Talk 2: Septotemporal variation in theta rhythm dynamics "

Speaker: Mark Brandon and Jake Hinman

Summary: Not provided

Relevant Materials:

http://www.sciencemag.org/content/332/6029/595.full

http://jn.physiology.org/content/105/6/2675.full.pdf+html

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October

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Date: Oct 14th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : " AMPA receptor trafficking in reconsolidation of context fear memories "

Speaker: Tom O Dell

Summary: Not provided

Relevant Materials:

http://www.nature.com/neuro/journal/v14/n10/full/nn.2907.html

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Date: Oct 28th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : " Mental Schema and its Neural Correlates"

Speaker: Balaji

Summary: Not provided

Relevant Materials:

http://www.sciencemag.org/content/333/6044/891.full

November

Date: Nov 04th

Time: 09:00 am

Place : 1st Floor Conference Room, Gonda building.

Title : " The Cytoplasmic Fragile X Mental Retardation Protein1 CYFIP1 is a Key Player in Neurodevelopment: The Link with Autism"

Speaker: Claudia Bagni

Date: Nov 18th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : " The h-currents, LTP,theta oscillations,grid cells and learning"

Speaker: Mayank Mehta

Summary: The hippocampal theta oscillations are thought to be critical for learning and memory and for the formation of entorhinal grid cells. Over the past few years the attention has been focused on the HCN1 channel: HCN1 channel knockout enhances theta rhythm and LTP, and improves spatial learning.

Two recent studies, one in the current issue of Neuron, from the Kandel lab, and another in the upcoming issue of Cell from the Moser lab, have measured the effect of HCN1 knockout on the entorhinal grid cells and hippocampal place cells, with many surprising results that compels us to rethink the cellular mechanisms governing grid cells and place cells.

Releavant Reading Material: http://www.sciencedirect.com/science?_ob=MiamiImageURL&_cid=272195&_user=4423&_pii=S0896627311007938&_check=y&_coverDate=2011-11-17&view=c&_gw=y&wchp=dGLzVlt-zSkzk&md5=9c0fb5a1be9056818c9b1daa13635cdf/1-s2.0-S0896627311007938-main.pdf

December

Date: Dec 9th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Reevaluating the Role of LTD in Cerebellar Motor Learning"

Speaker: Paul Mathews

Summary: It is widely believed that changes in the strength of synapses underlies the cellular changes responsible for memory formation. In the Cerebellum theories regarding the location of the cellular changes necessary for motor learning have recently been of great debate. One particular hypothesis proposed by Marr, Albus and Ito is that errors in motor behavior lead to changes in the strength of parallel fiber (PF) inputs onto Purkinje neurons (PNs). These errors, which are believed to be carried by climbing fiber terminals originating from the inferior olive, are thought to drive long term depressions (LTD) of PF-PN synapses that are activated coincidentally with the error signal. This change in the cerebellar circuit is believed, at least in part to underlie the cellular mechanisms driving motor learning. Supporting this hypothesis are numerous studies in which blocking the pathways responsible for PF-PN LTD leads to a deficit in cerebellar mediated motor behaviors. However, it has been argued that since these manipulations effect targets that often play multiple cellular regulatory roles (mGlur1/PKC, PKG, and αCamKII) the changes observed in motor behavior may be due instead to alterations in processes unrelated to the abolition of LTD. In the paper for discussion this Friday the authors reevaluate the role LTD plays in cerebellar motor learning by disrupting LTD through preventing AMPA receptor endocytosis directly rather than effecting more precocious molecules. Their experiments show that while these manipulations prevent associative PF-PN LTD in vitro numerous tests fail to show any significant behavioral effect of LTD disruption. For LMP this Friday we will examine the previous data suggesting LTD in the cerebellar cortex is critical for motor learning as well as how these new negative findings potentially alter our view of LTD’s role in cerebellar mediated motor learning.

Releavant Reading Material: http://www.sciencedirect.com/science?_ob=MiamiImageURL&_cid=272195&_user=4423&_pii=S0896627311001991&_check=y&_origin=&_coverDate=14-Apr-2011&view=c&wchp=dGLbVlS-zSkzk&md5=b2315bb5e6d206c4b2b051a7e8edf789/1-s2.0-S0896627311001991-main.pdf

Date: Dec 16th

Time: 09:30 am

Place : 2nd Floor Conference Room, Gonda building.

Title : "Synaptic Potentiation in the Central Amygdala upon Fear Learning"

Speaker: Ayako M. Watabe, Ph.D.