Previous weeks
Spring 2010:
January
Jan 15th
Speaker : John Guzowski of UC Irvine.
"Immediate-Early Gene Expression in Hippocampus: A Window into the Cellular Mechanisms & Neural Circuit Dynamics of Memory"
Summary of Talk:
The ability of neurons to change gene expression patterns in response to synaptic input is critical for cellular mechanisms underlying learning and memory. Following behavioral experience, expression of specific "immediate-early genes (IEGs)" is dramatically increased in discrete populations of neurons in hippocampus, neocortex, and subcortical brain regions. IEGs such as /Arc/ and /Homer 1a/ encode proteins capable of modifying synaptic function and are required for converting experience into lasting memory (i.e., memory consolidation). I will discuss past and ongoing research using sophisticated IEG imaging methods to study neural ensemble dynamics during learning and memory retrieval. In combining these imaging approaches with lesion, neuropharmacological, and vector-mediated gene knockdown/mutation methods, we are address long-standing and fundamental questions about the role of the hippocampus and associated neocortical regions in memory encoding, consolidation, and retrieval.
Jan 29th
Speaker : Dean Buonomano
"What is the Neural Basis of Priming "
Papers Covered:
Grill-Spector K, Henson R, Martin A (2006) Repetition and the brain: neural models of stimulus-specific effects. Trends in Cognitive Sciences 10:14-23.
Li L, Miller EK, Desimone R (1993) The representation of stimulus familiarity in anterior inferior temporal cortex. J Neurophysiol 69:1918-1929.
McMahon DBT, Olson CR (2007) Repetition Suppression in Monkey Inferotemporal Cortex: Relation to Behavioral Priming. J Neurophysiol 97:3532-3543.
February
Feb 05th
Speaker: Thomas W. Abrams, from Dept of Pharmacology, University of Maryland School of Medicine, Baltimore, MD.
"Molecular Mechanisms of Sensory Gating in Aplysia as a Model of Attention"
Summary of the Talk:
Sensory gating enables nervous systems to select which environmental stimuli receive attention. The sensory neuron-to-motor neuron synapse in the defensive withdrawal reflexes of the marine snail /Aplysia/ undergoes rapid and dramatic synaptic depression with low frequency activity. Although this phenomenon has been known for four decades, the underlying molecular mechanism has remained obscure. Our recent analysis suggests that synaptic depression in this system mediates a form of synaptic gating related to stimulus salience, rather than mediating a type of learning, habituation, based on familiarity with a stimulus. In my talk, I will discuss two opposing, calcium-dependent processes that flip these synapses between bistable states during sensory gating. The molecular elements in this switch include protein kinase C and the small G protein Arf. The ubiquitous presence of these highly conserved proteins among metazoans suggest that a similar sensory gating mechanism may operate in mammalian sensory systems, where it could contribute to attention.
Feb 19th
Speaker: Tom O'Dell
"The Death of the Subunit-Specific Rules Hypothesis of AMPA Receptor Trafficking?"
Summary of the Talk:
For many years the prevailing view regarding the mechanisms of AMPA receptor trafficking at excitatory synapses has held that the subunit composition of AMPA receptors has a crucial role. Via mechanisms dependent on the intracellular c-termini of the subunits, GluR2/GluR3 subunit containing receptors were thought to form a stable, continuously recycling pool of AMPA receptors at the synapse while GluR1/GluR2 subunit containing receptors were only trafficking into synapses in an activity-dependent manner. Once inserted into synapses, GluR1/GluR2 containing receptors were then thought to be gradually replaced by GluR2/GluR3 containing receptors. Along with other studies, recent work from the Nicoll laboratory using a single-cell “knockout” approach shows that there is very little role for GluR2/GluR3 containing receptors. Instead, 80% of all synaptic receptors (and 95% of all extrasynaptic receptors) are GluR1/GluR2 heteromers.
Relevant Papers:
Feb 26th
Speaker: Shlomo Dellal
"Heterogeneity in presynaptic bouton sensitivity to neuromodulators in parallel fibers of the cerebellar cortex."
Summary of the Talk:
In his presentation last Friday, Tom O’Dell brought up the possibility that there is heterogeneity in AMPAR subunit expression in different synapses in the same hippocampal pyramidal neuron. This may not be all that surprising for synapses formed by different presynaptic neuronal types and/or synapses in different regions of the neuron. The paper I’m presenting this week takes this a step further and shows that even neighboring synapses from the same neuron onto the same neuronal type, can exhibit significant heterogeneity. In this paper, the authors use calcium imaging to look at calcium transients in presynaptic boutons on cerebellar parallel fibers, which make excitatory synapses onto the sole output neuron for the cerebellum, the Purkinje cell. As with Schaffer collateral fibers and CA1 pyramidal cells in the hippocampus, these synapses are en passant. The authors look at the effects of activating various neuromodulator receptors on the presynaptic terminals, on stimulus-evoked calcium transients. They find that the sensitivity of neighboring boutons on the same axon to these drugs correlated with either the size of the bouton or the amplitude of the basal calcium transient. While the implications for cerebellar plasticity are unclear, these findings demonstrate that even neighboring synapses from the same neuron, possibly onto the same neuron, can exhibit remarkable differences in their molecular makeup that may influence their ability to undergo plasticity.
Relevant Papers:
March
Mar 05th
Speaker : Kelsey Martin
"Stable structural changes in cortical dendritic spines accompanies learning and memory."
Summary of the talk:
Not Provided
Relevant Papers:
Mar 12th
Speaker : Justin Shobe
Not all neurons are connected equally; a look at Hub neurons in the hippocampus
Summary of the talk:
In an exciting study in the December 4th issue of Science, Bonifazi and colleagues demonstrated the existence and importance of exceedingly rare but unusually richly connected cells in the developing hippocampus.Manipulating the activity of single GABAergic hub cells modulated network activity patterns, demonstrating their importance for coordinating synchronous activity. (Taken from preview by Case & Soltesz).
Relevant Papers:
Mar 19th
Speaker : Franklin B. Krasne
"Designing Fraidy Rat, a neurally plausible fear-learning automation"
Summary of the talk
Fraidy Rat is a computer program that incorporates a simulation of amygdala-centered fear learning and provides virtual tools (for behavioral analysis, stereotaxic surgery, single unit extracellular recording, electrical stimulation, targeted and systemic drug infusions) which students can use to try to discover how the automaton works, much in the same way as does a neuroscientist trying to understand real fear learning.The simulation at the center of the program is also intended as a model of fear-conditioning that I believe can contribute to the understanding of fear learning mechanisms. Both the program and the model will be discussed
April
Apr 02nd
Speaker: Peyman Golshani
Summary of the talk
Little is known about how neuronal populations encode memories in the human medial temporal lobe. In this exciting paper Erin Schuman and colleagues perform simultaneous local field potential and single unit recordings in the hippocampus and amygdala of humans while they encode and retrieve visual memories. They show that they can predict which memories are successfuly encoded by determining how tightly spikes are coordinated to theta oscillations of the field potential. Spike timing accuracy was more critical than the absolute firing rate or the power of theta oscillations. These experiments highlight the importance of spike-timing plasticity mechanisms in memory formation.
Relevant Paper:
