All events, All years

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

Trying to make sense of the cerebellum: models and experiments

Lecture
Date:
Tuesday, December 4, 2007
Hour: 12:15
Location:
Jacob Ziskind Building
Dr. Opher Donchin
|
Department of Biomedical Engineering Ben Gurion University, Beer Sheva

In this talk I will describe a recent controversy that has arisen regarding the intrinsic properties of Purkinje cells and explain the importance of this controversy to our understanding of Cerebellar function. In brief, it has been shown that Purkinje cell membrane potential is bistable, but there remains significant disagreement about whether this bistability has a functional role. In our lab, we addressed the controversy by recording from Purkinje cells in an awake animal and testing to see whether bistability that had been observed in vitro and in anaesthetized animals could also be seen in a behaving animal. Our findings will not settle the controversy, nor settle the question of the Cerebellum's functional role, but they will significantly shift the terms of the debate. We found that all of the predictions we tested confirmed the potential for a functional role for Purkinje cell bistability. This will force a serious re-evaluation of our understanding of Cerebellar circuitry.

The accessory olfactory (vomeronasal) system: a sensory adapted for social interactions

Lecture
Date:
Tuesday, November 20, 2007
Hour: 12:15
Location:
Jacob Ziskind Building
Dr. Shlomo Wagner
|
Dept of Biology and Dept of Neurobiology and Ethology, Haifa University

Many mammals rely on pheromones to mediate social interactions. Traditionally pheromones were thought to be detected by the accessory olfactory (vomeronasal) system, but recent studies indicated a central role for the main olfactory system in this function. Thus, unraveling the functional difference between these two chemosensory systems is essential for understanding pheromone-mediated social interactions. In this study we show that mitral cells of the accessory olfactory bulb respond to sensory input in a bimodal manner: a transient response is elicited by low level stimulation, whereas strong stimuli evoke sustained firing that lasts for 10-30 s. This is in sharp contrast to the unimodal response of main olfactory bulb mitral cells. We further show that this difference is dictated by distinct membrane properties of the two neuronal populations. We hypothesize that, via its sustained activity, the accessory olfactory system induces a new sensory state in the animal, reflecting its social context.

Clarifying the functional neuro-anatomy of face processing by combining lesion studies and neuroimaging

Lecture
Date:
Tuesday, November 13, 2007
Hour: 14:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Bruno Rossion
|
University of Louvain, Belgium

Understanding the functional neuro-anatomy of face processing in the human brain is a long-standing goal of Cognitive Neuroscience. Up to the early 90’s, the most important source of knowledge was from lesion studies, i.e. making correlations between the localization of lesions in groups of brain-damaged patients and their face recognition impairments. The influence of the cognitive approach in Neuropsychology, with an emphasis on single-case functional investigations, as well as the advent of neuroimaging studies in the healthy brain, have considerably reduced the importance of lesion studies in clarifying the neuro-anatomical aspects of face processing. In this talk, my goal will be to illustrate how neuroimaging investigations of single-cases of acquired prosopagnosic patients can still greatly increase our knowledge in this field. Neuroimaging studies of the normal brain have shown that the middle fusiform gyrus (‘FFA’) and the inferior occipital gyrus (‘OFA’) are activated by both detection and identification of faces. Among other observations, our studies of the patient PS, a case of prosopagnosia with normal object recognition, show that the right ‘FFA’ can be recruited to detect faces independently of the ‘OFA’ of the same hemisphere (Rossion et al., 2003). However, fMRI-adaptation investigations suggest that both areas are necessary to perform individual discrimination of faces (Schiltz et al., 2006). Recent observations also show that the the same brain area, here the right ‘FFA’, may be impaired at individual face discrimination while performing normal individual object discrimination. This suggests that clusters of neurons coding specifically for different categories in this area (Grill-Spector et al., 2006) can be functionnally independent. Finally, when structurally intact, non-face preferring areas such as the ventral part of the lateral occipital complex (vLOC) may subtend residual individual discrimination of faces following prosopagnosia. Altogether, these studies show that faces are processed through multiple pathways in the human brain, with a subset of these areas responding preferentially to faces being critical for efficient face recognition.

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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.

Novel mechanisms for stress-induced hippocampal dysfunction: dendritic spines and CRH

Lecture
Date:
Monday, March 12, 2007
Hour: 12:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Tallie Z. Baram
|
Prof. Pediatrics, Anatomy & Neurobiology and Neurology Danette Shepard Professor of Neurological Sciences, University of California at Irvine, Irvine CA

Whereas brain development is governed primarily by genetic factors, early-life experience, including stress, exerts long-lasting influence on neuronal structure and function. Baram's talk focuses on the hippocampus as the target of early-life stress because of its crucial role in learning and memory. The consequences of early-life stress on hippocampus-dependent cognitive tasks and synaptic plasticity will be described, as well as the the structural changes in dendrites and dendritic spines. New data will discuss the potential role of altered spine dynamics in the cellular mechanisms by which stress impacts the structure and function of hippocampal neurons.

The perception of curvature and its neural substrate

Lecture
Date:
Monday, March 5, 2007
Hour: 12:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Ohad Ben-Shahar
|
Department of Computer Science, Ben Gurion University of the Negev

The analysis of texture patterns, and texture segregation in particular, are at the heart of visual processing. In this work we question the accepted view that the (perceptual and computational) detection of salient perceptual singularities (i.e., borders) between perceptually coherent texture regions is tightly dependent upon feature *gradients*. Specifically, we study smooth orientation-defined textures (ODTs) and show psychophysically that they exhibit striking perceptual singularities even without any outstanding gradients in their defining feature (i.e., orientation). By studying oriented patterns from a (differential) geometric point of view we then develop a theory that accurately predicts their perceptual singularities from two ODT *curvatures*. Finally, in searching for the cortical substrate of curvature computation, we show how its critical role at the perceptual level could be reflected physiologically in the functional organization of the primary visual cortex via the connectivity patterns of long range horizontal connections.

Entorhinal grid cells and hippocampal memory

Lecture
Date:
Tuesday, February 27, 2007
Hour: 12:00
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Prof. Edvard I. Moser
|
Director, Centre for the Biology of Memory, Norwegian University of Science and Technology, Trondheim, Norway

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