All events, All years

Grouping by synchrony and precise temporal patterns in the visual cortex: evidence from voltage-sensitive dye imaging

Lecture
Date:
Sunday, June 22, 2008
Hour: 10:00
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Dr. Hamutal Slovin
|
Bar Ilan University

Accumulating psychophysical and physiological evidence suggest the involvement of early visual areas in the process of visual integration and specifically in local facilitation of proximal and collinear stimuli. To investigate the early integration mechanisms at the population level, we performed voltage-sensitive dye imaging that is highly sensitive to subthreshold population activity, and imaged from the primary visual cortex (V1) and extrastriate cortex (V2) of a behaving monkey. The animal was trained on a simple fixation task while presented with collinear or non-collinear patterns of small gratings, Gabors or short oriented bars. Facilitation in terms of increased amplitude activity at the corresponding retinotopic site of the target was observed for low contrast targets presented as part of collinear or non-collinear pattern. The facilitation effect and its time course depended on the target flanker separation distance, suggesting the role of horizontal connections. Next, we compared the dynamics of cortical response. We found that the time course of responses increased faster in the collinear pattern as compared with the non-collinear pattern. Finally, to study synchronization, we calculated the spatial correlation of pixels at the target location and found that correlation was higher for the collinear pattern, suggesting that the neuronal code for collinear versus non-collinear pattern may be carried by synchronization and response dynamics rather than simply maximal amplitude of response. These results suggest that neuronal population activity in area V1 is involved in local visual integration processes, and specifically in the increased sensitivity for low-contrast visual stimuli surrounded by high contrast flankers. In the second part of my talk I will discuss repeating spatio-precise spatio-temporal patterns. Numerous studies of neuronal coding have reported precise time relations among spikes in cortical neurons. Here our main goal was to study whether information processing in the cortex involves precise spatio-temporal patterns and to detect and characterize those patterns among neuronal populations exploiting voltage-sensitive dye imaging (VSDI) in visual cortical areas of a fixating monkey. Our preliminary results demonstrate that spatio-temporal patterns do exist above chance level (p<0.0001). The spatial characteristics of those patterns are consistent with physiological studies regarding the interplay between different visual areas, and the temporal characteristics show that the majority of the patterns appear in a range of 10-20ms apart

Timing and the olivo-cerebellar system

Lecture
Date:
Tuesday, June 17, 2008
Hour: 12:15
Location:
Jacob Ziskind Building
Prof. Yosef Yarom
|
Hebrew University of Jerusalem

The crystal-like anatomy and circuitry of the cerebellum and its preservation throughout vertebrate phylogeny suggest that it performs a single basic computation. It has been proposed that this basic computation is to create temporal patterns of activity necessary for timing motor, sensory and cognitive tasks. Despite the wide agreement about the involvement of the cerebellum in temporal coordination, there is an ongoing debate as to the neural mechanism that subserves this function. This debate stems from the current dogma that dominates cerebellar research. According to this dogma, PC simple spikes are evoked by input from granule cells and determine cerebellar nuclear (CN) activity, thus governing cerebellar output. The complex spikes, according to this view, serve as an error signal which is used by the system to readjust the simple spike activity. A novel theory of cerebellar function will be presented. According to this theory, the complex spike, rather than the simple spike, transmits the cerebellar output. The inferior olive generates accurate temporal patterns orchestrated by the cerebellar cortex and implemented in a variety of motor and non-motor tasks. Although this is a radical change of concept, it is well supported by experimental observations and it settles major problems inherent to the current dogma

Incubation of cocaine craving: behavioral and neuronal mechanisms

Lecture
Date:
Tuesday, June 10, 2008
Hour: 12:15
Location:
Jacob Ziskind Building
Dr. Yavin Shaham
|
National Institute on Drug Abuse, NIH

Abstract: Using a rat model of drug relapse and craving, we previously found time-dependent increases in cocaine seeking induced by exposure to drug cues after withdrawal from the drug, suggesting that cocaine craving incubates over time. In this lecture, I will first summarize our earlier behavioral and neurophysiological studies on incubation of cocaine craving. I will then discuss in more detail results from more recent studies implicating neuronal activity in the ventromedial prefrontal cortex and glutamate synaptic plasticity in the nucleus accumbens in the incubation of cocaine craving. I will also briefly address the relevance of our rat findings to the understanding of relapse to drug use in humans. Selected references related to incubation of cocaine craving Grimm JW, Hope B, Wise RA, Shaham Y (2001) Incubation of cocaine craving after withdrawal. Nature 412:141-142 Grimm JW, Lu L, Hayashi T, Su TP, Hope BT, Shaham Y (2003) Time dependent increases in brain-derived neurotrophic factor (BDNF) protein levels within the mesolimbic dopamine system following withdrawal from cocaine: implications for incubation of cocaine craving. The Journal of Neuroscience 23:742-747 Lu L, Dempsey J, Liu S, Bossert J, Shaham Y (2004) A single infusion of BDNF into the ventral tegmental area induces long-lasting potentiation of cocaine-seeking after withdrawal. The Journal of Neuroscience 24:1604-1611 Lu L, Grimm JW, Hope BT, Shaham Y (2004) Incubation of cocaine craving after withdrawal: a review of preclinical data. Neuropharmacology 47(S1): 214-227 (invited review for a special issue commemorating 30 years of NIDA research) Lu L, Hope BT, Dempsey J, Liu S, Bossert JM, Shaham Y (2005) Central amygdala ERK signaling pathway is critical to incubation of cocaine craving. Nature Neuroscience 8:212-219 Shaham Y, Hope BT (2005) The role of neuroadaptations in relapse to drug seeking. Nature Neuroscience 8:1437-1439 (special issue on Neurobiology of Addiction) Lu L, Uejima JL, Gray SM, Bossert JM, Shaham Y (2007) Systemic and central amygdala injections of the mGluR2/3 agonist LY379268 attenuate the expression of incubation of cocaine craving. Biological Psychiatry 61:591-598 Koya E, Uejima J, Wihbey K, Bossert JM, Hope BT, Shaham Y (2008) Role of ventral medial prefrontal cortex in incubation of cocaine craving. Neuropharmacology (in press, for a special issue commemorating 35 years of NIDA research)) Conrad KL, Tseng K, Uejima J, Reimers J, Heng L, Shaham Y, Marinelli M, Wolf ME (2008) Formation of accumbens GluR2-lacking AMPA receptors mediates incubation of cocaine craving. Nature (in press)

Single- and Double-Opponent Neurons in Primary Visual Cortex, and Their Different Roles in Color Perception

Lecture
Date:
Thursday, June 5, 2008
Hour: 13:30
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Prof. Robert Shapley
|
Center for Neural Science, New York University

Surrounding colors have a great influence on color perception. The reason is that the neural mechanisms of color perception need to make computations that take into account the spatial layout of the scene as well as the spectral reflectances of the target surface, in order to make color perception stable when illumination changes. It is not known how the visual system integrates form and color but it is now widely believed that the primary visual cortex, V1, plays an important role. Therefore, it is important to understand the spatial properties of V1 color-responsive neurons. Our investigations (in collaboration with Drs. Elizabeth Johnson and Michael Hawken) of color-responsive neurons in macaque monkey V1 revealed that there are two distinct groups of color-responsive cells in V1&#8212;single- and double-opponent cells&#8212;that have different functions in color perception. For example, V1 double-opponent cells are orientation-selective for pure color stimuli while single-opponent color cells are not. Double-opponent cells are selective for the spatial frequency of pure color stimuli while single-opponent color cells are very broadly tuned. The different types of color-responsive V1 cells probably both contribute to linking form and color, but in different ways.

Pain Selective Anesthesia

Lecture
Date:
Tuesday, June 3, 2008
Hour: 12:15
Location:
Jacob Ziskind Building
Dr. Alex Binshtok
|
Harvard Medical School, MA

Although pain is a complex entity, understanding the mechanisms of pain will reveal clues for better control. Perception of nociceptive, inflammatory and neuropathic pain - although initiated by distinctive mechanisms - all depend to some degree on generation and transmission of noxious signals by specific sets of primary sensory afferent neurons, nociceptors. Local anesthetics, by blocking voltage-gated sodium channels, prevent the transmission of nociceptive information and therefore block pain. However, since all local anesthetics act non-selectively on all types of axons, they also cause a loss of innocuous sensation, motor paralysis and autonomic block. Thus, approaches that produce only a selective blockade of pain fibers are of great potential clinical importance. In my talk, I will present a novel method to selectively block pain sensation. Using capsaicin to activate the TRPV1 channel, the noxious thermo-sensitive transducer localized specifically to high-threshold nociceptors, we were able to introduce QX-314, a membrane impermeable and therefore clinically ineffective lidocaine derivative, into nociceptors, and thereby blocked their electrical activity. Neurons that did not express TRPV1 were not blocked by the combination of QX-314 and capsaicin. Injection of QX-314 and capsaicin in vivo together but not alone abolished the response to noxious mechanical and thermal stimuli, without any motor or tactile deficit. This approach could be used clinically to produce long lasting regional analgesia while preserving motor and autonomic function. In addition to applications for dental procedures, surgery and childbirth, this technique could also be used to diminish postoperative and cancer pain, as well as inflammatory and neuropathic pain. Moreover, using TRP channels as a &#8220;natural&#8221; drug delivery system will enable specific cationic drugs to be targeted only to those cells that express the TRP channel. This technique offers a new strategy for treating pain.

Signal processing in neuronal networks: new vistas for calcium and noise

Lecture
Date:
Monday, June 2, 2008
Hour: 14:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Vladislav Volman
|
The Salk Institute

How neurons and neuronal networks perform signal processing tasks is one of the most important questions in neuroscience. Earlier research had focused on the integrative properties of individual neurons, and the role of activity-dependent inter-neuronal coupling remained obscure. We study the contribution of synaptic short-term plasticity to the detection, amplification, and storage of weak sensory stimuli in local neuronal circuits. Networks with fast plastic coupling show behavior consistent with stochastic resonance. Addition of slow asynchronous coupling mode leads to the qualitatively different properties of signal detection. Networks with asynchronous coupling also are able to hold information about the stimulus seconds after its cessation, thus representing a testable model of working memory, that is supported by experiments. Our results suggest a new, constructive, role in information processing for calcium-sustained synaptic &#8220;noise&#8221;.

Generation of dopamine neurons from embryonic stem cells for transplantation in Parkinson's disease

Lecture
Date:
Wednesday, May 28, 2008
Hour: 12:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof Anders Bjorklund
|
Lund University, Sweden

Fetal mesencephalic tissue has been used as a source of dopaminergic neurons for transplantation in clinical trials with Parkinson&#8217;s disease patients and in animal models of Parkinson&#8217;s disease. Due to the poor availability of human fetal tissue, and the ethical concerns associated with the use tissue from aborted fetuses, further development of the cell replacement therapy will critically depend on the access to alternative sources of cells for transplantation, based on the use of stem cells as a source of dopaminergic neurons. The recent discovery of Lmx1a and Msx1 as key determinant genes of mesencephalic dopaminergic neuron fate during development (Andersson et al. 2006) has opened new possibilities to drive undifferentiated stem cells towards fully functional mesencephalic dopaminergic neurons. Overexpression of these genes in stable embryonic stem (ES) cell lines is sufficient to generate neurons with almost 100% efficiency into a fully differentiated mesencephalic dopaminergic phenotype. The in vivo data obtained so far indicate that mesencephalic dopaminergic neurons can be generated in large numbers using this approach, and that they survive very well after transplantation to the striatum of 6-hydroxydopamine lesioned rats. In vivo, the Lmx1a- and Msx1-expressing cells develop into fully mature mesencephalic dopaminergic neurons, of both the A9 and A10 subtypes, and grow efficiently to form an extensive TH-positive axonal terminal network throughout the entire host striatum. Using this approach transplantable neurons with what appear to be a complete mesencephalic dopaminergic phenotype can be generated in large numbers from ES cell cultures.

Specialized mechanisms for face processing in the human brain

Lecture
Date:
Tuesday, May 27, 2008
Hour: 12:15
Location:
Jacob Ziskind Building
Dr. Galit Yovel
|
Tel Aviv University

It is well established that faces are processed by specialized mechanisms. I will first review evidence for the existence of face-specific processing mechanisms from cognitive studies, functional MRI and electrophysiology (Event-related potentials). These methods provide complementary information about the way information is processed in the brain. It is therefore important to determine whether they all reflect the same mechanism. Our data show that face-selective fMRI markers are strongly associated with cognitive markers of face-selective mechanisms. Furthermore, a simultaneous fMRI-ERP study reveals strong associations between face-selective fMRI regions and event-related potentials. Based on these findings, I will propose an integrated theory on how, where and when faces are represented at early stages of visual processing.

Does urocotin 1 matter?

Lecture
Date:
Monday, May 26, 2008
Hour: 12:00
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Tamas Kozicz
|
Dept of Cellular Animal Physiology Radboud University Nijmegen, The Netherlands

Interactions within the neurovascular unit underlying diseases of the cerebral cortex: evidence from human and animal studies

Lecture
Date:
Tuesday, May 20, 2008
Hour: 12:15
Location:
Jacob Ziskind Building
Prof. Alon Friedman
|
Ben Gurion University of the Negev

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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
|
Coll&egrave;ge 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&#8217;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 &#8220;simpler&#8221; 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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