All events, 2012

Neural Mechanisms Underlying Selective Attention at a Cocktail Party

Lecture
Date:
Sunday, December 30, 2012
Hour: 14:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Elana Zion Golumbic
|
Columbia University Medical Center, New York

Our ability to selectively attend to a particular conversation amidst competing input streams (e.g. other speakers) epitomized by the ‘Cocktail Party’ problem, is remarkable. How this demanding perceptual feat is achieved from a neural systems perspective remains unclear and controversial. In this talk I will present data from both invasive and non-invasive electrophysiological recordings in humans, investigating the manner in which selective attention governs the brain’s representation of attended and ignored speech streams using a simulated ‘Cocktail Party’ Paradigm. Results indicate that brain activity dynamically tracks speech streams using both low frequency phase and high frequency amplitude fluctuations, and that optimal encoding likely combines the two. In and near low level auditory cortices, attention ‘modulates’ the representation by enhancing cortical tracking of attended speech streams, but ignored speech remains represented. In higher order regions, the representation appears to become more ‘selective’. Furthermore, when to-be-ignored input has a predictable rhythmic structure, there is even evidence for active suppression of responses to these stimuli, making attention more effective. Viewing the facial movements of the speaker movements of a speech further enhances the selectivity of the neural response. Together, these findings are a testament to the proactive and flexible nature of the neural system which dynamically shapes its internal activity according to environmental and contextual demands.

Long-term dynamics of CA1 hippocampal neural ensemble representations of space

Lecture
Date:
Wednesday, December 26, 2012
Hour: 14:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Yaniv Ziv
|
Dept of Biology, Stanford University, CA

Hippocampal place cells are considered basic substrates of spatial memory, but the degree to which their ensemble representations of space are stable over long time periods has remained unmeasured. By using an integrated, miniature microscope, and micro-endoscope probes, we performed Ca2+-imaging in behaving mice as they repeatedly explored a familiar environment. This approach allowed us to track the place fields of thousands of CA1 hippocampal neurons over weeks. Spatial coding was highly dynamic, for on each day the neural representation of this environment involved a unique subset of neurons. A minority of the cells (~15–25%) overlapped between any two of these subsets and retained the same place fields. Although this overlap was also dynamic it sufficed to preserve a stable and accurate ensemble representation of space across weeks. These findings raise several important questions: What are the biological mechanisms that drive the turnover in the place cell membership of each day’s coding ensemble? What is the functional relevance of these dynamics to hippocampal memory? Overall, this work reveals a dynamic time-dependent facet of the hippocampal representation of space, and introduces a novel approach for investigating, in a behaving animal, how coding in large neuronal populations changes over long periods of time and as function of experience.

Sensory Selectivity in Random Cortical Circuits

Lecture
Date:
Tuesday, December 25, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Haim Sompolinsky
|
The Interdisciplinary Center for Neural Computation The Hebrew University, Jerusalem

Recent experiments indicate that primary auditory and visual cortex in rodents exhibit '"Salt and Pepper" architecture, consisting of highly selective neurons without columnar structure. Likewise, there is no apparent functional structure in the pattern of projections from the olfactory bulb to piriform cortex. In my talk I will address the questions: Can sharp stimulus selectivity be maintained in a cortical circuit with random connections? What are the computational ramifications of random cortical projections? How moderate tuning of cortical connectivity can be incorporated on top of largely random architecture? I will describe recent theoretical work that addresses these questions and will discuss their applications to sensory processing in rodent visual and olfactory cortices. I will also discuss relation between these results and recent developments in Machine Learning.

Of whiskers and blood: how mild sensory stimulation completely protects the cortex from an impending ischemic stroke

Lecture
Date:
Wednesday, December 12, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Ron Frostig
|
Dept of Neurobiology and Behavior University of California Irvine, CA

Stroke is a leading cause of death and long-term disability. In this talk, I will describe how a mild sensory stimulation (e.g., single whisker, tone) delivered to a rodent model of ischemic stroke (permanent occlusion of a major artery supplying blood to the cortex) can completely protect the cortex from an impending stroke. The mechanism underlying this surprising protection was revealed to be a new type of activity-dependent neurovascular plasticity. These findings will be presented in the context of our new understanding regarding the very large spread of evoked activity in sensory cortex supported by an underlying network of extremely long-range horizontal projections.

The legacy of Vivian Teichberg:Scavenging of excess brain glutamate to minimize neurological damage

Lecture
Date:
Tuesday, December 11, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. David Mirelman Dept of Biological Chemistry and Dr. Angela Ruban Dept of Neurobiology, WIS

Numerous clinical and preclinical investigators have reported that in several important medical indications such as in (i) ischemic stroke, (ii) traumatic brain injuries (TBI), (iii) acute migraine cases, (iv) glioblastoma brain tumors and (v) epileptic attacks, there is a rapid accumulation in the brain of excess glutamate molecules which are excitotoxic and this leads to significant neurological damage and motoric incapacitations in patients. Vivian Teichberg introduced a method for scavenging of excess brain glutamate which consists of the intravenous administration of a recombinant preparation of the enzyme, Glutamate Oxaloacetate Transaminase (GOT). This causes a rapid decrease in blood glutamate levels and creates a gradient which leads to the efflux of the excess brain glutamate into the blood stream and reduces neurological damage. The main advantage of the Brain Glutamate Scavenging technology, over other drug treatments that are currently being developed, is that the augmentation of GOT activity occurs in the blood circulation and therefore, doesn’t affect normal brain neurophysiology, whereas the pharmacological inhibition of the activities of glutamate receptors or transport systems occurs in the brain, and could be followed by serious side effects in the central nervous system.

Orbitofrontal cortex as a cognitive map of task space

Lecture
Date:
Wednesday, December 5, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Yael Niv
|
Department of Psychology, Princeton University

Orbitofrontal cortex (OFC) has long been known to play an important role in decision making. However, the exact nature of that role has remained elusive. The OFC does not seem necessary for almost anything---animals and humans can learn, unlearn and reverse previous learning even without an OFC, albeit more slowly than their healthy counterparts. What role, then, can the OFC be playing such that its absence would cause subtle but broadly permeating deficits? We propose a new unifying theory of OFC function. Specifically, we hypothesize that OFC encodes a map of the states of the current task and their inter-relations, which provides a state space for reinforcement learning elsewhere in the brain. I will first use a simple perceptual judgement task to demonstrate that state spaces, a critical ingredient in any reinforcement learning algorithm, are learned from data. I will then use our hypothesis that the OFC encodes the learned state space to explain recent experimental findings in an odor-guided choice task (Takahashi et al, Nature Neuroscience 2012) as well as classic findings in reversal learning and extinction. Finally, I will lay out a number of testable experimental predictions that can distinguish our theory from other accounts of OFC function.

Multiple decision systems in the human brain

Lecture
Date:
Tuesday, December 4, 2012
Hour: 14:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Nathaniel Daw
|
Center for Neural Science, New York University

The spiking of dopamine neurons in animals, and apparently analogous BOLD signals at dopaminergic targets in humans, appear to report predictions of future reward. Prominent computational theories of these responses suggest that they both support and reflect trial-and-error learning about which actions have been successful, based on simple associations with past rewards. This is essentially a neural implementation of Thorndike's (1911) behaviorist principle that reinforced behaviors should be repeated. However, it has long been known that organisms are not condemned merely to repeat previously successful actions, but instead that even rodents' decisions can under some circumstances reflect other sorts of knowledge about task structure and contingencies. The neural and computational bases for these additional effects, and their interaction with the putative reinforcement systems in the basal ganglia, are poorly understood. Such interactions are of considerable practical importance because, for instance, disorders of compulsion in humans, such as substance abuse, are thought to arise from runaway reinforcement processes unfettered by more deliberative influences. I first discuss how such extra-reinforcement effects – e.g., planning novel routes based on cognitive maps, or incorporating "counterfactual" feedback about foregone actions – can be incorporated in the framework of existing computational theories, via algorithms for “model-based reinforcement learning." Rather than learning about actions' past successes directly, such algorithms learn a representation of the task structure, and can use it to evaluate candidate actions via mental simulation of their consequences. This computational characterization allows reasoning about (and explaining empirical data concerning) under which circumstances the brain might efficiently adopt either this strategy or the reinforcement one. It also allows quantifying and dissociating either strategy's effects on decision making and associated neural signaling. Next, I discuss human fMRI experiments characterizing these influences in learning tasks. By fitting computational models to decision behavior and BOLD signals, we demonstrate that neither choices nor (putatively dopamine-related) BOLD signals in striatum can be explained by past reinforcement alone, but instead that both reflect additional learning and reasoning about task structure and contingencies. That such influences are prominent even at the level of striatum challenges current models of the computations there and suggest that the system is a common target for many different sorts of learning. Additional experiments examine individual variation in the tendency to employ either system; the patterns of both spontaneous and experimentally induced variation suggest that the dominance of model-based decision influence over simpler reinforcement systems employs cognitive control mechanisms that have previously been studied in other areas of cognitive neuroscience. Finally, I report results showing that patients with several disorders involving compulsion show abnormally reinforcement-bound choices on our tasks, supporting a link between these neurocomputational learning mechanisms and pathological habits.

Aging of the Mind:Immunity in the middle of mind/body relationship

Conference
Date:
Monday, December 3, 2012
Hour:
Location:
David Lopatie Conference Centre

Homepage

What can parasitoid wasps teach us about decision making in the brain of insects?

Lecture
Date:
Tuesday, November 27, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Frederic Libersat
|
Life Sciences Dept, Ben Gurion University of the Negev, Beer Sheva

Much like humans, animals may choose to initiate behavior based on their "internal state" rather than as a response to external stimuli alone. The neuronal underpinnings responsible for generating this ‘internal state’, however, remain elusive. The parasitoid jewel wasp hunts cockroaches to serve as a live food supply for its offspring. The wasp stings the cockroach in the head and delivers a neurotoxic venom cocktail directly inside the prey’s cerebral ganglia to apparently ‘hijack its free will’. Although not paralyzed, the stung cockroach becomes a living yet docile ‘zombie’ incapable of self-initiating walking or escape running. We demonstrate that the venom selectively depresses the cockroach’s motivation or ‘drive’ to initiate and maintain walking-related behaviors, rather than inducing an overall decrease in arousal or a ‘sleep-like’ state. Such a decrease in the drive for walking can be attributed to a decrease in neuronal activity in a small region of the cockroach cerebral nervous system, the sub-esophageal ganglion (SEG). Specifically, we have used behavioral, neuro-pharmacological and electrophysiological methods to show that artificial focal injection of crude milked venom or procaine into the SEG of non-stung cockroaches decreases spontaneous and evoked walking, as seen with naturally-stung cockroaches. Moreover, spontaneous and evoked neuronal spiking activity in the SEG, recorded with an extracellular bipolar microelectrode, is markedly decreased in stung cockroaches as compared with non-stung controls. By injecting a venom cocktail directly into the SEG, the parasitoid Jewel Wasp selectively manipulates the cockroach’s motivation to initiate walking without interfering with other non-related behaviors.

Moving beyond category-selectivity: What can fMRI tell us about large-scale interactions in vision?

Lecture
Date:
Wednesday, November 21, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Assaf Harel
|
Laboratory of Brain and Cognition, National Institute of Mental Health (NIMH), NIH

Visual perception is commonly viewed as a stimulus-driven process, whereby neural representations of increasing complexity are hierarchically assembled from primary sensory areas through category-selective regions to high-level association areas. Vision provides a great opportunity to study cortical mechanisms of perception, as the ordered hierarchical organization has been amply demonstrated and modeled formally in many computational models. Despite their success, however, computational models rarely perform as well as the biological system, and often fail to take account of the highly interactive nature of cortical networks - involving interactions between different processing pathways as well as across different levels of the hierarchy. In the current talk, I will present a series of neuroimaging studies, which demonstrate how representations in dedicated brain regions in visual cortex emerge from interactions with large-scale networks, exemplifying both functional and neuroanatomical constraints. Specifically, I will describe recent investigations of object- and scene-selective cortex that reveal (1) the large impact that top-down factors, such as experience and task demands have on the neural representations of visual objects and (2) how the distinction between object and scene representations can be accounted for by the patterns of connectivity within and across the ventral and dorsal visual processing pathways.

Pages

All events, 2012

Neural Mechanisms Underlying Selective Attention at a Cocktail Party

Lecture
Date:
Sunday, December 30, 2012
Hour: 14:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Elana Zion Golumbic
|
Columbia University Medical Center, New York

Our ability to selectively attend to a particular conversation amidst competing input streams (e.g. other speakers) epitomized by the ‘Cocktail Party’ problem, is remarkable. How this demanding perceptual feat is achieved from a neural systems perspective remains unclear and controversial. In this talk I will present data from both invasive and non-invasive electrophysiological recordings in humans, investigating the manner in which selective attention governs the brain’s representation of attended and ignored speech streams using a simulated ‘Cocktail Party’ Paradigm. Results indicate that brain activity dynamically tracks speech streams using both low frequency phase and high frequency amplitude fluctuations, and that optimal encoding likely combines the two. In and near low level auditory cortices, attention ‘modulates’ the representation by enhancing cortical tracking of attended speech streams, but ignored speech remains represented. In higher order regions, the representation appears to become more ‘selective’. Furthermore, when to-be-ignored input has a predictable rhythmic structure, there is even evidence for active suppression of responses to these stimuli, making attention more effective. Viewing the facial movements of the speaker movements of a speech further enhances the selectivity of the neural response. Together, these findings are a testament to the proactive and flexible nature of the neural system which dynamically shapes its internal activity according to environmental and contextual demands.

Long-term dynamics of CA1 hippocampal neural ensemble representations of space

Lecture
Date:
Wednesday, December 26, 2012
Hour: 14:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Yaniv Ziv
|
Dept of Biology, Stanford University, CA

Hippocampal place cells are considered basic substrates of spatial memory, but the degree to which their ensemble representations of space are stable over long time periods has remained unmeasured. By using an integrated, miniature microscope, and micro-endoscope probes, we performed Ca2+-imaging in behaving mice as they repeatedly explored a familiar environment. This approach allowed us to track the place fields of thousands of CA1 hippocampal neurons over weeks. Spatial coding was highly dynamic, for on each day the neural representation of this environment involved a unique subset of neurons. A minority of the cells (~15–25%) overlapped between any two of these subsets and retained the same place fields. Although this overlap was also dynamic it sufficed to preserve a stable and accurate ensemble representation of space across weeks. These findings raise several important questions: What are the biological mechanisms that drive the turnover in the place cell membership of each day’s coding ensemble? What is the functional relevance of these dynamics to hippocampal memory? Overall, this work reveals a dynamic time-dependent facet of the hippocampal representation of space, and introduces a novel approach for investigating, in a behaving animal, how coding in large neuronal populations changes over long periods of time and as function of experience.

Sensory Selectivity in Random Cortical Circuits

Lecture
Date:
Tuesday, December 25, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Haim Sompolinsky
|
The Interdisciplinary Center for Neural Computation The Hebrew University, Jerusalem

Recent experiments indicate that primary auditory and visual cortex in rodents exhibit '"Salt and Pepper" architecture, consisting of highly selective neurons without columnar structure. Likewise, there is no apparent functional structure in the pattern of projections from the olfactory bulb to piriform cortex. In my talk I will address the questions: Can sharp stimulus selectivity be maintained in a cortical circuit with random connections? What are the computational ramifications of random cortical projections? How moderate tuning of cortical connectivity can be incorporated on top of largely random architecture? I will describe recent theoretical work that addresses these questions and will discuss their applications to sensory processing in rodent visual and olfactory cortices. I will also discuss relation between these results and recent developments in Machine Learning.

Of whiskers and blood: how mild sensory stimulation completely protects the cortex from an impending ischemic stroke

Lecture
Date:
Wednesday, December 12, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Ron Frostig
|
Dept of Neurobiology and Behavior University of California Irvine, CA

Stroke is a leading cause of death and long-term disability. In this talk, I will describe how a mild sensory stimulation (e.g., single whisker, tone) delivered to a rodent model of ischemic stroke (permanent occlusion of a major artery supplying blood to the cortex) can completely protect the cortex from an impending stroke. The mechanism underlying this surprising protection was revealed to be a new type of activity-dependent neurovascular plasticity. These findings will be presented in the context of our new understanding regarding the very large spread of evoked activity in sensory cortex supported by an underlying network of extremely long-range horizontal projections.

The legacy of Vivian Teichberg:Scavenging of excess brain glutamate to minimize neurological damage

Lecture
Date:
Tuesday, December 11, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. David Mirelman Dept of Biological Chemistry and Dr. Angela Ruban Dept of Neurobiology, WIS

Numerous clinical and preclinical investigators have reported that in several important medical indications such as in (i) ischemic stroke, (ii) traumatic brain injuries (TBI), (iii) acute migraine cases, (iv) glioblastoma brain tumors and (v) epileptic attacks, there is a rapid accumulation in the brain of excess glutamate molecules which are excitotoxic and this leads to significant neurological damage and motoric incapacitations in patients. Vivian Teichberg introduced a method for scavenging of excess brain glutamate which consists of the intravenous administration of a recombinant preparation of the enzyme, Glutamate Oxaloacetate Transaminase (GOT). This causes a rapid decrease in blood glutamate levels and creates a gradient which leads to the efflux of the excess brain glutamate into the blood stream and reduces neurological damage. The main advantage of the Brain Glutamate Scavenging technology, over other drug treatments that are currently being developed, is that the augmentation of GOT activity occurs in the blood circulation and therefore, doesn’t affect normal brain neurophysiology, whereas the pharmacological inhibition of the activities of glutamate receptors or transport systems occurs in the brain, and could be followed by serious side effects in the central nervous system.

Orbitofrontal cortex as a cognitive map of task space

Lecture
Date:
Wednesday, December 5, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Yael Niv
|
Department of Psychology, Princeton University

Orbitofrontal cortex (OFC) has long been known to play an important role in decision making. However, the exact nature of that role has remained elusive. The OFC does not seem necessary for almost anything---animals and humans can learn, unlearn and reverse previous learning even without an OFC, albeit more slowly than their healthy counterparts. What role, then, can the OFC be playing such that its absence would cause subtle but broadly permeating deficits? We propose a new unifying theory of OFC function. Specifically, we hypothesize that OFC encodes a map of the states of the current task and their inter-relations, which provides a state space for reinforcement learning elsewhere in the brain. I will first use a simple perceptual judgement task to demonstrate that state spaces, a critical ingredient in any reinforcement learning algorithm, are learned from data. I will then use our hypothesis that the OFC encodes the learned state space to explain recent experimental findings in an odor-guided choice task (Takahashi et al, Nature Neuroscience 2012) as well as classic findings in reversal learning and extinction. Finally, I will lay out a number of testable experimental predictions that can distinguish our theory from other accounts of OFC function.

Multiple decision systems in the human brain

Lecture
Date:
Tuesday, December 4, 2012
Hour: 14:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Nathaniel Daw
|
Center for Neural Science, New York University

The spiking of dopamine neurons in animals, and apparently analogous BOLD signals at dopaminergic targets in humans, appear to report predictions of future reward. Prominent computational theories of these responses suggest that they both support and reflect trial-and-error learning about which actions have been successful, based on simple associations with past rewards. This is essentially a neural implementation of Thorndike's (1911) behaviorist principle that reinforced behaviors should be repeated. However, it has long been known that organisms are not condemned merely to repeat previously successful actions, but instead that even rodents' decisions can under some circumstances reflect other sorts of knowledge about task structure and contingencies. The neural and computational bases for these additional effects, and their interaction with the putative reinforcement systems in the basal ganglia, are poorly understood. Such interactions are of considerable practical importance because, for instance, disorders of compulsion in humans, such as substance abuse, are thought to arise from runaway reinforcement processes unfettered by more deliberative influences. I first discuss how such extra-reinforcement effects – e.g., planning novel routes based on cognitive maps, or incorporating "counterfactual" feedback about foregone actions – can be incorporated in the framework of existing computational theories, via algorithms for “model-based reinforcement learning." Rather than learning about actions' past successes directly, such algorithms learn a representation of the task structure, and can use it to evaluate candidate actions via mental simulation of their consequences. This computational characterization allows reasoning about (and explaining empirical data concerning) under which circumstances the brain might efficiently adopt either this strategy or the reinforcement one. It also allows quantifying and dissociating either strategy's effects on decision making and associated neural signaling. Next, I discuss human fMRI experiments characterizing these influences in learning tasks. By fitting computational models to decision behavior and BOLD signals, we demonstrate that neither choices nor (putatively dopamine-related) BOLD signals in striatum can be explained by past reinforcement alone, but instead that both reflect additional learning and reasoning about task structure and contingencies. That such influences are prominent even at the level of striatum challenges current models of the computations there and suggest that the system is a common target for many different sorts of learning. Additional experiments examine individual variation in the tendency to employ either system; the patterns of both spontaneous and experimentally induced variation suggest that the dominance of model-based decision influence over simpler reinforcement systems employs cognitive control mechanisms that have previously been studied in other areas of cognitive neuroscience. Finally, I report results showing that patients with several disorders involving compulsion show abnormally reinforcement-bound choices on our tasks, supporting a link between these neurocomputational learning mechanisms and pathological habits.

What can parasitoid wasps teach us about decision making in the brain of insects?

Lecture
Date:
Tuesday, November 27, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Frederic Libersat
|
Life Sciences Dept, Ben Gurion University of the Negev, Beer Sheva

Much like humans, animals may choose to initiate behavior based on their "internal state" rather than as a response to external stimuli alone. The neuronal underpinnings responsible for generating this ‘internal state’, however, remain elusive. The parasitoid jewel wasp hunts cockroaches to serve as a live food supply for its offspring. The wasp stings the cockroach in the head and delivers a neurotoxic venom cocktail directly inside the prey’s cerebral ganglia to apparently ‘hijack its free will’. Although not paralyzed, the stung cockroach becomes a living yet docile ‘zombie’ incapable of self-initiating walking or escape running. We demonstrate that the venom selectively depresses the cockroach’s motivation or ‘drive’ to initiate and maintain walking-related behaviors, rather than inducing an overall decrease in arousal or a ‘sleep-like’ state. Such a decrease in the drive for walking can be attributed to a decrease in neuronal activity in a small region of the cockroach cerebral nervous system, the sub-esophageal ganglion (SEG). Specifically, we have used behavioral, neuro-pharmacological and electrophysiological methods to show that artificial focal injection of crude milked venom or procaine into the SEG of non-stung cockroaches decreases spontaneous and evoked walking, as seen with naturally-stung cockroaches. Moreover, spontaneous and evoked neuronal spiking activity in the SEG, recorded with an extracellular bipolar microelectrode, is markedly decreased in stung cockroaches as compared with non-stung controls. By injecting a venom cocktail directly into the SEG, the parasitoid Jewel Wasp selectively manipulates the cockroach’s motivation to initiate walking without interfering with other non-related behaviors.

Moving beyond category-selectivity: What can fMRI tell us about large-scale interactions in vision?

Lecture
Date:
Wednesday, November 21, 2012
Hour: 12:30
Location:
Gerhard M.J. Schmidt Lecture Hall
Dr. Assaf Harel
|
Laboratory of Brain and Cognition, National Institute of Mental Health (NIMH), NIH

Visual perception is commonly viewed as a stimulus-driven process, whereby neural representations of increasing complexity are hierarchically assembled from primary sensory areas through category-selective regions to high-level association areas. Vision provides a great opportunity to study cortical mechanisms of perception, as the ordered hierarchical organization has been amply demonstrated and modeled formally in many computational models. Despite their success, however, computational models rarely perform as well as the biological system, and often fail to take account of the highly interactive nature of cortical networks - involving interactions between different processing pathways as well as across different levels of the hierarchy. In the current talk, I will present a series of neuroimaging studies, which demonstrate how representations in dedicated brain regions in visual cortex emerge from interactions with large-scale networks, exemplifying both functional and neuroanatomical constraints. Specifically, I will describe recent investigations of object- and scene-selective cortex that reveal (1) the large impact that top-down factors, such as experience and task demands have on the neural representations of visual objects and (2) how the distinction between object and scene representations can be accounted for by the patterns of connectivity within and across the ventral and dorsal visual processing pathways.

Structural clues to a visual function: direction selectivity in the retina

Lecture
Date:
Tuesday, November 13, 2012
Hour: 13:00
Location:
Gerhard M.J. Schmidt Lecture Hall
Prof. Sebastian Seung
|
MIT

For a mechanistic understanding of brain function, it is important to understand the relation between patterns of activity and connectivity in neural networks. My lab is studying this relation in the retina by classifying its neurons into cell types, and mapping the connections between types. I will describe preliminary results concerning the connections of the J type of ganglion cell, and what they suggest about the mechanism of its direction selectivity. To enable our neuroscience research, we have used machine learning and social computing to build systems that analyze light and electron microscopic images through a combination of artificial and human intelligence. The most exciting recent example is EyeWire, an online community that mobilizes the public to map the retinal connectome by playing a coloring game. I will conclude by describing our beginning efforts to search for the cell assembly, a pattern of connectivity hypothesized by Hebb in 1949 as a structural basis of long-term memory.

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All events, 2012

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All events, 2012

Aging of the Mind:Immunity in the middle of mind/body relationship

Conference
Date:
Monday, December 3, 2012
Hour:
Location:
David Lopatie Conference Centre

Homepage

Optogenetics symposium

Conference
Date:
Saturday, July 14, 2012
Hour:
Location:
David Lopatie Conference Centre

90th Birthday Meeting for Prof. David Samuel

Conference
Date:
Thursday, June 28, 2012
Hour:
Location:
Michael Sela Adutitorium

Homepage

Brain Sciences Open Day

Conference
Date:
Wednesday, March 7, 2012
Hour:
Location:
David Lopatie Conference Centre

Homepage

Mini-Symposium-Windows into the Mind:New Approaches to Brain and Cognition

Conference
Date:
Tuesday, January 3, 2012
Hour:
Location:
Arthur and Rochelle Belfer Building for Biomedical Research

Homepage