All events, All years

Motor learning with unstable neural representations

Lecture
Date:
Wednesday, January 9, 2008
Hour: 11:30
Location:
Wolfson Building for Biological Research
Dr. Uri Rokhni
|
MIT

It is usually assumed that the brain learns by changing neural circuits that are otherwise stable. However, recent experiments in monkeys show that the neural representation of movement in motor cortex is continually changing even without learning, when practicing a familiar task. We set to investigate the reason for these changes. We analyzed the empirical data and found that the changes are slow and random. We constructed a theoretical model of a cortical network that learns a motor skill by changing synaptic strengths. Our model explains how the network can change its synaptic strengths, and neural activity, without changing the motor behavior. Additionally, our model replicates the observed changes when synaptic learning is assumed highly noisy. We speculate that this noise serves to explore different synaptic configurations during learning.

TRP channels, what are they and why are they important

Lecture
Date:
Tuesday, January 8, 2008
Hour: 12:15
Location:
Jacob Ziskind Building
Prof. Baruch Minke
|
Hebrew University, Jeruslaem

TRP channels constitute a large and diverse family of proteins that are expressed in many tissues and cell types. The TRP superfamily is conserved throughout evolution from nematodes to humans. The name TRP is derived from a spontaneously occurring Drosophila mutant lacking TRP that responded to a continuous light with a Transient Receptor Potential (therefore, it was designated TRP by Minke). The Drosophila TRP and TRP-like (TRPL) channels, which are activated by the inositol lipid signaling cascade, were used later on to isolate the first mammalian TRP homologues. TRP channels mediate responses to light, nerve growth factors, pheromones, olfaction, taste, mechanical, temperature, pH, osmolarity, vasorelaxation of blood vessels, metabolic stress and pain. Furthermore, mutations in members of the TRP family are responsible for several diseases. Although a great deal is known today about members of the mammalian TRP channels, the exact physiological function and gating mechanisms of most channels are still elusive. Removal of divalent open channel block by depolarization plays a critical role in learning and memory, which is mediated by the N-methyl-D-aspartate (NMDA) channel. TRP channels also exhibit open channel block, but the physiological mechanism of its removal is still unknown. We found that lipids produced by phospholipase C (PLC) and hypoosmotic solutions remove divalent open channel block from the Drosophila TRPL channels without depolarization. Application of lipids increased single channel current and caused impermeable cation influx. The tarantula peptide GsMTx-4 specifically blocks a range of stretch-activated channels, but not by specific interaction with the channel proteins themselves but rather by modification of the channel-lipid boundary. The GsMTx-4 toxin blocked the lipids effect on TRPL channels. We found remarkable commonality between the effects of lipids on the Drosophila TRPL and the mammalian NMDA channels. We suggest a new lipid-dependent mechanism to alleviate open channel block, which operates under physiological conditions, in synergism with depolarization. The profound effect of lipids modulation allows cross talk between channel activity and lipid-producing pathways. Joint work with Moshe Parnas, Ben Katz & Shaya Lev

"A hierarchy of temporal receptive windows

Lecture
Date:
Tuesday, January 1, 2008
Hour: 12:00
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Dr. Uri Hasson
|
New York University

Real-world events unfold at different time scales, and therefore cognitive and neuronal processes must likewise occur at different time scales. In the talk I will present a novel procedure that identifies brain regions responsive to the preceding sequence of events (past time) over different time scales. The fMRI activity was measured while observers viewed silent films presented forward, backward, or piecewise-scrambled in time. The results demonstrate that responses in different brain areas are affected by information that has been accumulated over different time scales, with a hierarchy of temporal receptive windows spanning from short (~4 s) to intermediate (~12 s) and long (~ 36 s). Thus, although we adopted an open-ended experimental protocol (free viewing of complex stimuli), we found that parametric manipulation of the temporal structure of a complex movie sequence produced lawful changes in cortical activity across different brain regions. In addition to the reliable cortical response patterns, I will also show that films exerted considerable control over the subjects' behavior (i.e., eye movements or galvanic skin responses). Finally, I will present few applications of this method for studying the neuronal correlates of complex human behaviors under more natural settings.

Astroglial metabolic networks sustain hippocampal synaptic transmission"

Lecture
Date:
Monday, December 31, 2007
Hour: 12:30
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Dr. Nathalie Rouach
|
Collège de France, Paris

Glucose is the major source of energy utilized by the brain and is transported by the blood. However, it has been proposed that neurons obtain most of their energy from extracellular lactate, a glucose metabolite produced by astrocytes. Interestingly, astrocytes provide a physical link to the vasculature by their perivascular endfoot processes and are organized in network thanks to extensive intercellular communication through gap junctions. The aim of this work was to determine whether the connectivity of local astrocyte networks contributes to their metabolic supportive function to neurons. The expression of connexins 43 and 30 (Cx43, Cx30), the two main gap junction proteins in astrocytes, was particularly enriched in perivascular endfeet of astrocytes and delineated blood vessel walls in mouse hippocampal slices. Glucose trafficking dynamics was examined at the single-cell level using the fluorescent glucose derivative 2-NBDG (2- ([N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2 deoxyglucose). When injected for 20 minutes by whole cell recordings in single astrocytes lining blood vessels, 2-NBDG diffused through the astrocyte gap junction-mediated network, with a preferential pathway along interconnected astrocyte endfeet around blood vessels. This traffic was activity dependent, being reduced in the presence of TTX and increased during repetitive synaptic stimulation or epileptic conditions, and involved the activation of glutamatergic AMPA receptors. Interestingly, the permeability of Cx43, but not Cx30, was selectively regulated by glutamatergic neuronal activity. In contrast 2-NBDG, dialysed in CA1 pyramidal cells or interneurons, did not diffuse to other cells. Exogenous glucose deprivation induces a slow depression of synaptic transmission in hippocampal slices, suggesting that intrinsic energy reserves sustain neurotransmission. To test whether glucose from astrocytic networks can sustain synaptic activity, fEPSPs were recorded during exogenous glucose deprivation, while dialysing intracellularly glucose in a single astrocyte via a patch pipette. Depression of fEPSP during exogenous glucose deprivation was inhibited when glucose was administered to the astrocytic network. This effect was not caused by leakage of glucose in the extracellular space, as it was not observed in the double knockout mice for Cx30 and Cx43, devoid of gap-junction coupling. Altogether these results indicate that gap junctions play a role in the metabolic supportive function of astrocytes by providing an activity-dependent intercellular route for glucose delivery from blood vessels to distal neurons.

Silence of the Genes-The two faces of RNA interference: involvement of miRNAs in brain development but also a tool to study brain disorders

Lecture
Date:
Thursday, December 27, 2007
Hour: 11:00
Location:
Wolfson Building for Biological Research
Dr. Oded Singer
|
The Salk Institute

"Exploring the molecular mechanisms of axon pruning"

Lecture
Date:
Wednesday, December 26, 2007
Hour: 10:00
Location:
Jacob Ziskind Building
Dr. Oren Schuldiner
|
Stanford University

Pruning of exuberant neuronal connections is a widespread mechanism utilized to refine neural circuits during the development of both vertebrate and invertebrate nervous systems. Despite recent studies, our knowledge about the molecular mechanisms of this pruning process remains limited. I will describe two forward genetic screens that I have conducted to identify new molecules involved in axon pruning of the gamma neurons in the Drosophila mushroom body, which I study as a model for developmental axon pruning. In the first screen, I used conventional chemical mutagenesis to generate mutants which I then screened using a mosaic technique invented in the lab called MARCM (Mosaic Analysis with a Repressible Cell Marker), which enables positive labeling of a single mutant clone. I will show that a mutation in a gene encoding an uncharacterized trans-membrane protein belonging to the Ig superfamily causes inhibition of pruning. The tedious mapping of this chemical mutagenesis mutant drove my motivation to create a new methodology of screening. I will present the generation of an insertion mutagenesis library based on the piggyBac transposon that results in mutants that are easily mapped and are ready for mosaic analysis. While screening the collection of over 3000 mutants that I have generated, I identified several genes that are involved in axon pruning. I will describe in depth the characterization of a novel, postmitotic role for the cohesin complex, in regulating various aspects of neuronal mutagenesis incuding axon pruning. Lastly, I will show preliminary data implicating a few other genes such as a kinsesin and JNK, in axon pruning.

Cortical attractors: intermittent insight into multiple

Lecture
Date:
Tuesday, December 25, 2007
Hour: 12:00
Location:
Jacob Ziskind Building
Prof. Alessandro Treves
|
SISSA, Trieste, Italy & University for Science and Technology, Trondheim,Norway

I will discuss different models that implement distinct limit cases of the Braitenberg view of the cortex as a two-level associative network, with A (long-range) and B (local) systems of connections. In one limit case, local networks are assumed structureless, and they can be collapsed onto single Potts variables in order to analyse global cortical dynamics, and the effect of macroscopic correlations. In another limit case, local nets have internal metric connectivity, which can be exploited to code continuous parameters topographically, a "where" representation. This models allow to analyse a local version of the what/where dilemma, a conflict to which evolution has proposed multiple solutions, all, frankly, unsatisfactory...I will discuss different models that implement distinct limit cases of the Braitenberg view of the cortex as a two-level associative network, with A (long-range) and B (local) systems of connections. In one limit case, local networks are assumed structureless, and they can be collapsed onto single Potts variables in order to analyse global cortical dynamics, and the effect of macroscopic correlations. In another limit case, local nets have internal metric connectivity, which can be exploited to code continuous parameters topographically, a "where" representation. This models allow to analyse a local version of the what/where dilemma, a conflict to which evolution has proposed multiple solutions, all, frankly, unsatisfactory...

Internally generated cell assembly sequences in the

Lecture
Date:
Tuesday, December 18, 2007
Hour: 12:00
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Prof. Gyorgy Buzsaki
|
Rutgers University, New Jersey, USA

The dominant theoretical form of mental structure of the last century was implicitly a neuropsychological model. At the center of this model, necessary for episodic free recall, planning or logical reasoning, is Hebb’s phase sequences of neuronal assemblies, i.e., hypothetical self-propagating loops of neuronal coalitions connected by modifiable synapses. These phase sequences can be activated by exogenous or endogenous (internal) sources of stimulation, independent from environmental determinants of behavior. The neurophysiological implication of this conjecture for episodic recall is that hippocampal networks are endowed by an internal mechanism that can generate a perpetually changing neuronal activity even in the absence of environmental inputs. Recall of similar episodes would generate similar cell assembly sequences, and uniquely different sequence patterns would reflect different episodes. Using large-scale recording of neuronal ensembles in the behaving rat, I will show experimental support of self-perpetuating activity neuronal assemblies. The physiological characteristics of these assemblies are virtually identical to the feature of hippocampal place cells controlled by environmental and/or idiothetic stimuli. I hypothesize that neuronal substrates introduced for navigation in “simpler” animals are identical to those needed for memory formation and recall.

Persistence and Phase Synchronization Properties of Fixational Eye Movements

Lecture
Date:
Sunday, December 16, 2007
Hour: 14:00
Location:
Wolfson Building for Biological Research
Dr. Shay Moshel
|
Minerva Center & Department of Physics Bar Ilan University, Ramat Gan

The biological visual system is extremely complex; the coordination between the neurological system, the ocular muscles, and the photoreceptors of the retina make it possible for the visual system to produce a continues 3D representation of the real world which provides the ability to distinguish between objects in space, track them, and estimate their relative distances and velocities. For such complex abilities, the retinal image should be persistent enough for the brain to evaluate it, but ephemeral enough to permit a high sampling rate and in order to overcome physical limitations on constant exposure of the photoreceptors. In order to provide accurate depth information it is also required that there is a synchronization between the movement of both eyes. These requirementS are addressed by a complex neuromuscular system that produces multitimescale and synchronization behaviors that are not yet fully understood. We investigated the roles of these different time scale behaviors, especially how they are expressed in the different spatial directions (vertical versus horizontal). In addition, in primates with frontally placed eyes, the synchronization properties of fixational eye movements is related to binocular coordination in order to provide stereopsis, and thus this was also investigated. Results show different scaling behavior between horizontal and vertical movements. When the small ballistic movements, i.e., microsaccades, are removed, the scaling behavior in both axis become similar. Our findings suggest that microsaccades enhance the persistence at short time scales mostly in the horizontal component and much less in the vertical component. We here applied also the phase synchronization decay method to study the synchronization between six combinations of binocular fixational eye movement components. We found that only the right and left horizontal are synchronized with each other and the right and left vertical. Furthermore, the vertical components are significantly more synchronized than the horizontal components. These differences may be due to the need for continuously moving the eyes in the horizontal plane, in order to match the stereoscopic image for different viewing distances.

Can economics learn something from measuring time response?

Lecture
Date:
Tuesday, December 11, 2007
Hour: 12:15
Location:
Jacob Ziskind Building
Prof. Ariel Rubinstein
|
School of Economics, Tel Aviv University & Dept of Economics, New York University

The lecture will use the results about time response (see Rubinstein (2007), http://arielrubinstein.tau.ac.il/papers/78.pdf ) to discuss the potential meaning of the neuroeconomics approach to economics. Before the lecture please respond to the 15min questionnaire posted at: http://gametheory.tau.ac.il/student/poll.asp?group=1391

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The Hippocampus and Memory: Consolidation or Transformation?

Lecture
Date:
Tuesday, May 29, 2007
Hour: 12:00 - 13:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Gordon Winocur
|
Rotman Research Institute, Toronto, Ontario, Canada

Adaptation and integration in the multimodal space map of the barn owl

Lecture
Date:
Monday, May 21, 2007
Hour: 12:00 - 13:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Yoram Gutfreund
|
Dept of Physiology & Biophysics, Faculty of Medicine, Technion, Haifa

Linking Network Archtecture to Neural Coding in the Olfactory System

Lecture
Date:
Monday, May 7, 2007
Hour: 12:00 - 13:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Roni Jortner
|
Interdisciplinary Center for Neural Computation Hebrew University of Jerusalem and Computation and Neural Systems, California Institute of Technology

Learning induces new representations of instructions and actions in the motor cortex

Lecture
Date:
Monday, April 30, 2007
Hour: 12:00 - 13:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Eilon Vaadia
|
Dept of Physiology, Faculty of Medicine, The Hebrew University of Jerusalem

Structural analysis of serotonin transporter mechanism and regulation

Lecture
Date:
Wednesday, April 18, 2007
Hour: 12:00 - 13:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Gary Rudnick
|
Dept of Pharmacology Yale University School of Medicine

Auditory self-perception and gating in a songbird

Lecture
Date:
Tuesday, April 17, 2007
Hour: 12:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Richard Hahnloser
|
Institute of Neuroinformatics, UZH/ETHZ, Zurich

Vocal production and learning rely on the evaluation of auditory feedback. We use the songbird as a model system for exploring how auditory feedback in vocalizing animals is represented by auditory brain areas, and how auditory signals are gated back into premotor areas involved in song production and learning. We expose juvenile zebra finches to distorted auditory feedback and record from neurons in field L, an avian forebrain area thought to be analogous to mammalian primary auditory cortex. Most field L neurons in our ongoing study do not respond to auditory perturbation during singing, despite their motor-related firing being similar to auditory responses to playback of the bird’s own song. We argue that this behaviour of field L neurons is reminiscent of mirror neurons in primate inferior frontal cortex. In adult birds, we demonstrate modulation and gating of auditory and spontaneous cerebral activity by the thalamic nucleus uveaformis (Uva): The normal dependence of premotor-like spike patterns (bursts) on the behavioural state can be reversed by pharmacological manipulation of Uva activity. Our results show that avian thalamic relay neurons have a function that is reminiscent of a mixture of functions attributed to relay and reticular neurons in the mammalian thalamus. In summary, our findings of corollary motor discharges in auditory brain areas and of explicit thalamic gating mechanisms help to advance the understanding of auditory feedback processing and sensorimotor integration for complex learned behaviors.

guilt by association: Memory context effects, source memory, and the frontal lobes

Lecture
Date:
Monday, April 16, 2007
Hour: 12:00 - 13:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Daniel Levy
|
Gonda Brain Research Center, Bar-Ilan University & Dept of Neurobiology, WIS

As in many domains of cognition, the effects of context on memory are ubiquitous and pervasive. Even memory-impaired neurological patients and aging individuals with deficits in direct source recollection benefit from context reinstatement during retrieval. Though context effects on free and cued recall are robust, findings regarding context effects on recognition have been widely divergent. We have proposed a multifactorial model of context effects that takes into account the impact of hippocampally-based target-context binding, anterior medial temporal lobe-based additive familiarity, and frontal lobe-based strategic processes that suppress response bias to acheive mnemonic advantages. I will discuss findings from simulations and neuropsychological studies of the elderly that illustrate these factors. I will also present new data that suggest differences between temporal and spatial context and discuss their implications for memory models.

Epigenetic mechanisms in memory formation

Lecture
Date:
Sunday, April 15, 2007
Hour: 12:00 - 13:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. David Sweatt
|
Head, Neurobiology Dept and Mcknight Brain Institute, University of Alabama, Birmingham AL

Dr. Sweatt's seminar will focus on molecular mechanisms underlying learning and memory. Dr. Sweatt uses knockout and transgenic mice to investigate signal transduction mechanisms in the hippocampus, a brain region known to be critical for higher-order memory formation in animals and humans. His talk will describe transcriptional regulation in memory formation, focusing on studies of transcription factors, regulators of chromatin structure, and other epigenetic mechanisms, in order to understand the role of regulation of gene expression in synaptic plasticity and memory.

Optimal decoding of neural population responses in the primate visual cortex

Lecture
Date:
Monday, March 26, 2007
Hour: 12:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Eyal Seidemann
|
Center for Perceptual Systems and Depts. of Psychology and Neurobiology The University of Texas at Austin

How are simple perceptual decisions formed based on noisy neural signals that are distributed over large populations of neurons in early sensory cortical areas? To begin to address this fundamental question, we used a combination of real-time imaging andvelectrophysiological techniques to measure directly population responses in the primary visual cortex (V1) of monkeys while they performed a reaction-time visual detection task. We then evaluated different candidate models for detecting the target from the measured neural responses. Our analysis reveals that previously proposed methods for pooling neural responses over space and time are highly inefficient given the statistics of V1 population responses. We derived the optimal decoder of V1 responses and show that it can be approximated by simple neural circuits. Finally, we show that an optimal decoder that uses the signals from the monkey's cortex can outperform the monkey, indicating that inefficiencies at, or downstream to, V1 limit performance in simple detection tasks. The list of people I would like to meet with that I've sent to Alon is only partial. I'll be happy to meet with anyone in the Dept. that is available and is interested in meeting with me.

Medial frontal cortex involvement in error processing and delay discounting

Lecture
Date:
Monday, March 19, 2007
Hour: 12:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Steven D. Forman
|
University of Pittsburgh, School of Medicine, Pittsburgh, PA

Background: Opiate addicts entering methadone maintenance treatment exhibit decreased medial frontal cortex activation with occurrence of error (negative) events. The strength of this error-related cortical signal correlated with discrimination performance and moment-to-moment cognitive control. In the clinical setting the strength of this signal predicted individual treatment adherence (e.g., time maintained in treatment before drop-out). While the latter finding suggests a connection between error processing and complex decisions involving choices between immediate and delayed goals, we did not have direct evidence supporting this connection. Methods: Subjects performed both the Go/NoGo task and a delay-discounting task while brain activity was monitored using event-related fMRI. Results: The medial frontal cortex region previously associated with error processing also displayed significant activation during delay discounting. Moreover, the individual strength of brain activation while processing errors correlated with that exhibited during processing decisions between immediate and delayed hypothetical rewards. Supported by NIH grant DA11721 and VA CPPF and MERIT awards.

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