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Computational Model of Spatio-Temporal Cortical Activity in V1: Mechanisms Underlying Observations of Voltage Sensitive Dyes

Lecture
Date:
Thursday, October 29, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Prof. David McLaughlin
|
Provost and Professor of Mathematics and Neuroscience New York University

To investigate the existence and the characteristics of possible cortical operating points of the primary visual cortex, as manifested by the coherent spontaneous ongoing activity revealed by real-time optical imaging based on voltage-sensitive dyes, we studied numerically a very large-scale (_5 _ 105) conductancebased, integrate-and-fire neuronal network model of an _16-mm2 patch of 64 orientation hypercolumns, which incorporates both isotropic local couplings and lateral orientation-specific long-range connections with a slow NMDA component. A dynamic scenario of an intermittent desuppressed state (IDS) is identified in the computational model, which is a dynamic state of (i) high conductance, (ii) strong inhibition, and (iii) large fluctuations that arise from intermittent spiking events that are strongly correlated in time as well as in orientation domains, with the correlation time of the fluctuations controlled by the NMDA decay time scale. Our simulation results demonstrate that the IDS state captures numerically many aspects of experimental observation related to spontaneous ongoing activity, and the specific network mechanism of the IDS may suggest cortical mechanisms and the cortical operating point underlying observed spontaneous activity.In addition, we address the functional significance of the IDS cortical operating points by investigating our model cortex response to the Hikosaka linemotion illusion (LMI) stimulus—a cue of a quickly flashed stationary square followed a few milliseconds later by a stationary bar. As revealed by voltage-sensitive dye imaging, there is an intriguing similarity between the cortical spatiotemporal activity in response to (i) the Hikosaka LMI stimulus and (ii) a small moving square. This similarity is believed to be associated with the preattentive illusory motion perception. Our numerical cortex produces similar spatiotemporal patterns in response to the two stimuli above, which are both in very good agreement with experimental results. The essential network mechanisms underpinning the LMI phenomenon in our model are (i) the spatiotemporal structure of the LMI input as sculpted by the lateral geniculate nucleus, (ii) a priming effect of the long-range NMDA-type cortical coupling, and (iii) the NMDA conductance–voltage correlation manifested in the IDS state. This mechanism in our model cortex, in turn, suggests a physiological underpinning for the LMI-associated patterns in the visual cortex of anaesthetized cat.

Locust swarms and their immunity

Lecture
Date:
Sunday, October 4, 2009
Hour: 12:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Gabriel Miller
|
Harvard University

Locusts are arguably the most notorious pests in history, directly affecting the livelihood of 1 in 10 people worldwide. These fascinating insects exhibit dramatic phenotypic plasticity in response to environmental fluctuation, changing from shy and cryptic 'solitarious' forms to brightly-colored and swarming 'gregarious' forms. How do these swarms form? What triggers this phenotypic switch? I will discuss how the experience of locust females influences the phenotype of her offspring, and how the 'gregarizing factor' underlying this maternal effect was isolated, purified, and partially characterized. Finally, I present field and laboratory data suggesting that swarm formation (and this gregarizing factor) affects locust immune function.

Learning in Recurrent Networks with Spike-Timing Dependent Plasticity

Lecture
Date:
Wednesday, September 23, 2009
Hour: 12:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Klaus Pawelzik
|
Institute for Theoretical Physics, Dept of Neuro-Physics University of Bremen, Germany

Memory contents are believed to be stored in the efficiency of synapses in recurrent networks of the brain. In prefrontal cortex it was found that short and long term memory is accompanied with persistent spike rates [1,2] indicating that reentrant activities in recurrent networks reflect the content of synaptically encoded memories [3]. It is, however, not clear which mechanisms enable synapses to sequentially accumulate information from the stream of patterned inputs which under natural conditions enter as perturbations of the ongoing neuronal activities. For successful incremental learning only novel input should alter specific synaptic efficacies while previous memories should be preserved as long as network capacity is not exhausted. In other words, synaptic learning should realise a palimpsest property with erasing the oldest memories first. Here we demonstrate that synaptic modifications which sensitively depend on /temporal changes /of pre- and the post-synaptic neural activity can enable such incremental learning in recurrent neuronal networks. We investigated a realistic rate based model and found that for robust incremental learning in a setting with sequentially presented input patterns specific adaptation mechanisms of STDP are required that go beyond the observed synaptic changes for sequences of pre- and post-synaptic spikes [4]. Our predicted pre- and post-synaptic adaptation of synaptic changes in response to respective rate changes are experimentally testable and --if confirmed-- would suggest that STDP provides an unsupervised learning mechanism particularly well suited for incremental memory acquisition by circumventing the stability-plasticity dilemma.

Molecular mechanisms of neuron-glia interactions: roles in development and disease

Lecture
Date:
Tuesday, September 22, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Prof. Gabriel Corfas
|
F.M. Kirby Neurobiology Center Harvard Medical School

Why is visual perception multi-stable?

Lecture
Date:
Tuesday, September 8, 2009
Hour: 12:30
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Prof. Jochen Braun
|
Cognitive Biology Group Otto-von-Guericke-University Magdeburg, Germany

Visual experience is an extrapolation of the retinal image on the basis of prior knowledge about the visual environment. Intriguingly, this inferential process frequently fails to reach a definitive conclusion so that visual experience of a stable scene continues to fluctuate between alternative percepts. This multi-stability of visual perception has long been attributed to adaptive processes that curtail the persistence of any dominant percept. However, more and more evidence points to a fundamentally stochastic, fluctuation-driven nature of multi-stable perception. We have discovered subtle regularities in series of perceptual alternations that allow us to quantify the relative contributions of adaptive and stochastic processes to perceptual reversals. In collaboration with Gustavo Deco, Barcelona, we have used our observations to constrain a generic attractor network model for multi-stable perception (Moreno-Bote et al., 2007). In the context of this model, our measurements imply that multi-stable perception consistently straddles the dividing line between the oscillatory (adaptation dominated) and the bistable (fluctuation-driven) regimes. In other words, visual perception seems to be maintained in a state of criticality. Excitable networks are known to respond most sensitively and with maximal dynamic range when in a state of criticality. Accordingly, visual perception may be maintained in a critical state in order to maximize sensitivity, with multi-stability as an unavoidable side-effect. Our conclusions throw a surprising new light on many well-known observations and raise several new questions. For example, they imply the existence of hitherto unsuspected homeostatic mechanisms.

“Tomorrow is another day": A 24 h persistent synaptic plasticity in hippocampal interneuron circuits

Lecture
Date:
Tuesday, August 18, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Dr. Israeli Ran
|
Dept of Physiology University of Montreal, Canada

Hippocampal interneurons synchronize the activity of large neuronal ensembles during memory consolidation. Although the latter process is manifested as increases in synaptic efficacy which require new protein synthesis in pyramidal neurons, it is unknown whether such enduring plasticity occurs in interneurons. In the present talk, I will discuss a long-term potentiation (LTP) of transmission at individual interneuron excitatory synapses which persists for at least 24 h, after repetitive activation of type-1 metabotropic glutamate receptors [mGluR1-mediated chemical late LTP (cL-LTPmGluR1 )]. cL-LTPmGluR1 involves pre- and postsynaptic expression mechanisms and requires both transcription and translation via phosphoinositide 3-kinase/mammalian target of rapamycin and MAPkinase kinase extracellular signal-regulated protein kinase signaling pathways. Moreover, cL-LTPmGluR1 involves translational control at the level of initiation as it is prevented by hippuristanol, an inhibitor of eIF4A, and facilitated in mice lacking the cap-dependent translational repressor, 4E-BP. These results reveal novel mechanisms of long-term synaptic plasticity that are transcription and translation-dependent in inhibitory interneurons, indicating that persistent synaptic modifications in interneuron circuits may contribute to hippocampal-dependent cognitive processes.

Active Sensing by Bat Biosonar: Strategies of Information Flow Control

Lecture
Date:
Monday, August 17, 2009
Hour: 12:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Marc Holderied
|
University of Bristol, UK

Abstract: Echolocation or biosonar is an alien sense to humans. For us as visually guided mammals it is hard to imagine what an echolocator's acoustic perception of its surroundings 'looks' like. Part of this difficulty arises because vision and biosonar differ fundamentally in a number of ways: a) Vision is based on two dimensional data, i.e. images focused on the retina in the eye, while bats evaluate a linear stream of echoes and have to reconstruct all directional/spatial information from the temporal and spectral properties of the echo stream; b) the number of sensory cells in hearing is much lower than in vision and c) biosonar is a case of active sensing, i.e. bats actively produce the signals with which they probe the environment, while vision (in the vast majority of cases) relies on external light sources. This combination of traits, i.e. limited bandwidth and active sensing has led to a number of behavioural adaptive strategies by which bats control what information about the environment becomes available to them. In a sense, external mechanisms to extract the relevant information from the plethora of available data are far more important in biosonar than in vision. Hence, biosonar offers unique opportunities to study behavioural strategies of information flow control by active sensing. We employed high resolution acoustic tracking techniques and 3D laser scanning of natural habitats to study free flying bats in forests. We investigated how they adapt flight patterns, calling behaviour and sonar signal design to optimize information flow.

Movement selectivity in the human mirror system

Lecture
Date:
Tuesday, July 28, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Ilan Dinstein New York University Visiting PhD Student – Malach Lab

Abstract: “Monkey mirror neurons are unique visuomotor neurons that respond when executing a particular movement (e.g. grasping, placing, or manipulating) and also when passively observing someone else performing that same movement. Importantly, subpopulations of mirror neurons respond in a selective manner to one preferred movement whether executed or observed. It has been proposed that the activity of mirror neurons underlies the monkey’s ability to perceive the goals and intentions of others. Human mirror neurons are thought to exist in two cortical areas, the anterior intraparietal sulcus (aIPS) and the ventral premotor (vPM), which have been called the human mirror system. A dysfunction in the responses of this system has been hypothesized to cause impairment in the ability to understand one another resulting in Autism. I will talk about three studies where we characterized the responses of the human mirror system using fMRI adaptation and classification techniques to assess their response selectivity for observed and executed hand movements. Two studies were performed with neurotypical individuals and the third with Autistic individuals.”

Role of Dopamine in Reward: Anatomical and Conceptual Issues

Lecture
Date:
Tuesday, July 14, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Dr. Satoshi Ikemoto NIDA (Nat. Inst. on Drug Abuse) Behavioral Neuroscience Research Branch NIH, USA

Abstract: The mesolimbic dopamine system from the ventral tegmental area (VTA) to the ventral striatum has been implicated in reward. Using intracranial self-administration procedures, we found that rats learn to self-administer cocaine or amphetamine into the medial portion of the ventral striatum more readily than the lateral ventral striatum. Rats learn to self-administer drugs such as opiates and cholinergic drugs into the posterior portion of the VTA more readily than the anterior VTA. Axonal tracer experiments revealed that the medial ventral striatum is preferentially innervated by dopamine neurons localized in the posterior VTA, while the lateral ventral striatum is preferentially innervated by dopamine neurons in the anterolateral VTA. Therefore, the mesolimbic dopamine system from the posterior VTA to the medial ventral striatum appears to be more responsive for rewarding effects of drugs. In addition, we have studied the nature of the rewarding effects of drugs. We found that noncontingent administration of cocaine or amphetamine into the medial ventral striatum increases leverpressing, when leverpressing contingently elicits visual signals. These results suggest that a function of dopamine in the ventral striatum is to facilitate actions in response to salient stimuli. Dopamine in the medial ventral striatum also appears to facilitate associative learning as shown by conditioned place preference of cocaine. We suggest that ventral striatal dopamine induces an arousing state that facilitates ongoing appetitive responding and reinforcement.

Collective Motion and Decision-Making in Animal Groups

Lecture
Date:
Thursday, July 9, 2009
Hour: 12:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Iain Couzin
|
Dept of Ecology and Evolutionary Biology and Program in Computational and Mathematical Biology Princeton University USA

Grouping organisms, such as schooling fish, often have to make rapid decisions in uncertain and dangerous environments. Decision-making by individuals within such aggregates is so seamlessly integrated that it has been associated with the concept of a “collective mind”. As each organism has relatively local sensing ability, coordinated animal groups have evolved collective strategies that allow individuals to access higher-order computational abilities at the collective level. Using a combined theoretical and experimental approach involving insect and vertebrate groups, I will address how, and why, individuals move in unison and investigate the principles of information transfer in these groups, particularly focusing on leadership and collective consensus decision-making. An integrated "hybrid swarm" technology is introduced in which multiple robot-controlled replica individuals interact within real groups allowing us new insights into group coordination. These results will be discussed in the context of the evolution of collective biological systems.

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Synergistic Interactions Between Molecular Risk Factors of Alzheimer’s Disease

Lecture
Date:
Tuesday, March 24, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Prof. Daniel Michaelson
|
Dept of Neurobiology, Tel Aviv University

The allele E4 of apolipoprotein E (apoE4), the most prevalent genetic risk factor for Alzheimer’s disease, is associated with elevated levels of brain amyloid. This led to the suggestion that the pathological effects of apoE4 are mediated via synergistic pathological interactions with amyloid β (Aβ). We have recently shown that activation of the amyloid cascade by inhibition of the Aβ-degrading enzyme neprilysin in brains of apoE3 and apoE4 mice results in the isoform specific degeneration in apoE4 mice, of hippocampal CA1 neurons and of entorhinal and septal neurons. This is accompanied by the accumulation of intracellular Aβ and apoE and by pronounced cognitive deficits in the ApoE4 mice. We presently investigated the cellular mechanisms underlying the apoE4 dependent Aβ mediated neurodegeneration of CA1 and septal neurons and their neuronal specificity. Confocal microscopy kinetic studies revealed that the accumulated Aβ in CA1 neurons of apoE4 mice co-localizes with lysosomes and is associated with lysosomal activation and subsequent apoptotic neuronal cell death. Furthermore the accumulated Aβ is oligomerized. In contrast the degeneration of septal neurons is not associated with oligomerization of the accumulated Aβ. Instead intracellular Aβ in septal neurons co-localizes with the apoE receptor LRP whose levels are specifically elevated in these cells. These findings suggest that the apoE4 dependent Aβ mediated neurodegeneration is related, in CA1 but not in septal neurons, to oligomerization of the accumulated Aβ. In addition, neurodegeneration of CA1 but not of septal neurons is associated with inflammatory activation suggesting that the brain area specificity of the effects of apoE4 and Aβ are also related to brain area specific non neuronal mechanisms such as inflammation. Neuronal plasticity experiments revealed that apoE4 inhibits synaptogenesis and neurogenesis and stimulates apoptosis in hippocampal neurons of apoE4 mice that have been exposed to an enriched environment. These effects are also associated with the specific accumulation of apoE4 and oligomerized Aβ in the affected neurons. Additional experiments revealed that apoE4 up-regulates the expression of inflammation-related genes following i.c.v injection of LPS and that this effect is also associated with the accumulation of intra neuronal Aβ in hippocampal neurons. These findings suggest that the impaired neuronal plasticity and hyper inflammatory effects of apoE4 may also be mediated via cross talk interactions of apoE4 with the amyloid cascade.

Now I See It, Now I Don’t: Neural Basis of Simple Perceptual Decisions in the Human Brain

Lecture
Date:
Wednesday, March 18, 2009
Hour: 12:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Tobias H. Donner
|
Center for Neural Science & Dept of Psychology New York University

It is frequently proposed that conscious perceptual decisions are produced by recurrent interactions among multiple brain areas. Sensory stimuli, which are close to psychophysical threshold or perceptually bistable, induce fluctuating percepts in the face of constant sensory input. Thus, these stimuli provide ideal tools for probing the intrinsic neural mechanisms underlying perceptual decisions, in the absence of extrinsic stimulus changes. I will present human neuroimaging (MEG and fMRI) studies, in which we used this approach for probing the large-scale neural mechanisms underlying decisions about the presence or absence of simple visual features. Our results suggest that neural population activity in parietal, prefrontal, and premotor areas reflects the decision process, and that population activity in extrastriate ventral visual cortex reflects perception. Further, cooperative and competitive long- range interactions, across multiple levels of the cortical processing hierarchy, both seem to underlie simple perceptual decisions.

How circadian clocks keep time: insights from Drosophila

Lecture
Date:
Tuesday, March 17, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Dr. Sebastian Kadener
|
Dept of Biological Chemistry The Hebrew University of Jerusalem

Circadian rhythms in locomotor activity are an example of a well-characterized behavior for which the molecular and neurobiological bases are not yet completely understood. These rhythms are self-sustained 24 hours rhythms that underlie most physiological and behavioral processes. The central circadian clock, which is situated in the brain, is responsible for daily rhythms in locomotor activity that persist even after weeks in constant darkness (DD). Peripheral clocks are spread trough the fly body and regulate a plethora of physiological functions that include: olfaction, detoxification and immunity. All these clocks keep time trough complex transcriptional-translational feedback loops that include the proteins CLK, CYC, PER and TIM. My research focuses on the study of the molecular basis of the circadian clock. In particular, I am interested in the contribution of the different molecular interactions and processes to the generation of robust 24hs rhythms. In this context, I have recently demonstrated that transcriptional speed of the clock gene PER is a determinant of the circadian period and that translational regulation by miRNAs is part of the central circadian clock.

Complex Translational Control in the Gustatory Cortex Determines the Stability of a Taste Memory

Lecture
Date:
Thursday, March 12, 2009
Hour: 12:00
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Dr. Kobi Rosenblum
|
Dept of Neurobiology, University of Haifa

The off-line processing of acquired sensory information in the mammalian cortex is an example for the unique way biology creates to compute and store information which guides behavior. The relatively short temporal phase in the process (i.e. hours following acquisition) is defined biochemically by its sensitivity to protein synthesis inhibitors. Until recently this negative definition of molecular consolidation did not reveal the details of the endogenous processes taking place, minutes to hours, in the neurons and circuit underlying a given memory. We use taste learning paradigms in order to study this process of molecular consolidation in the gustatory cortex. Recent results, from our laboratory, obtained from genetic, pharmacological, biochemical, electrophysiological and behavioral studies demonstrate that translational control, at the initiation and elongation phases of translation, plays a key role in the process of molecular consolidation. Moreover, this spatially and temporally regulated translation control modifies both general and synaptic protein expression that is crucial for memory stabilization. We propose a model to explain the interplay between regulation of initiation and elongation phases of translation and demonstrate that in certain situations cognitive enhancement can be achieved.

Unravelling signal processing in the cortical column

Lecture
Date:
Tuesday, February 24, 2009
Hour: 12:30
Location:
Jacob Ziskind Building
Prof. Idan Segev
|
Department of Neurobiology & Interdisciplinary Center for Neural Computation Hebrew University, Jerusalem

Never before have such intense experimental efforts been focused on neuronal circuits of the size of few hundred thousands neurons whose functions are relatively well defined. The extraordinarily powerful new genetic tools and 3D reconstruction methods, combined with modern multi-electrode arrays, telemetry, two-photon imaging and photo-activation are starting to shed bright light on the intricacies of these circuits, and in particular of the cortical column. But without tools that integrate all this different types of data, one cannot expect to gain a comprehensive understanding on how these circuits perform specific sensory-motor or cognitive functions. As in any other complex system, a modeling study is essential if we are to ever say that we understand how this system works. I will describe several attempts in my group to begin building detailed models of the cortical column, highlighting that, at both circuit level and at the level of individual neurons, models should capture experimental variability and that the building of these models should become automated. I will demonstrate how these models could be used to fruitfully guide new experiments and discuss were all this new integrated "simulation-driven brain research agenda" might lead to.

“Intersectional Optogenetics" unearths neurons that drive fish locomotion

Lecture
Date:
Wednesday, February 18, 2009
Hour: 15:00
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Prof. Ehud Isacoff
|
Dept of Molecular & Cell Biology UC Berkeley

A major challenge for biology is to develop new ways of determining how proteins operate in complexes in cells. This requires molecularly focused methods for dynamic interrogation and manipulation. An attractive approach is to use light as both input and output to probe molecular machines in cells. While there has been significant progress in optical detection of protein function, little advance has been made in remote control of any kind, including optical methods. As part of our efforts in the NIH Nanomedicine Development Center for the Optical Control of Biological Function, we are developing methods for rapidly switching on and off with light the function of select proteins in cells. The strategies are broadly applicable across protein classes. Our approach has been to synthesize Photoswitched Tethered Ligands (PTLs), which are attached in a site directed manner to a protein of interest. The site of attachment is designed into the protein to be at a precise distance from a binding site for the ligand. The geometric precision has two important consequences. First, light of two different wavelengths is used to isomerize the linker in such a way that the ligand can only bind in one of the sites, thus making it possible to toggle binding on and off with light. Second, native proteins are not affected by the PTL and remain insensitive to light, since the PTL does not attach. This means that a specific protein in a cell, a tissue and even in an intact freely behaving organism, can have its biochemical signaling turned on and off by remote optical control. The switching is very fast, taking place in ~1 millisecond, i.e. at the rate of the fastest nerve impulse. I will describe how we used our light-gated kaintate-type glutamate receptor, LiGluR, to study vertebrate locomotion. We used intersectional optogenetics in larval zebrafish to identify a new class of neurons that provide an important modulatory drive to swim behavior.

Computing as modeling

Lecture
Date:
Tuesday, February 17, 2009
Hour: 12:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Prof. Oron Shagrir
|
Dept of Philosophy & Dept of Cognitive Science Hebrew University, Jerusalem

The view that the brain computes is a working hypothesis in cognitive and brain sciences. But what does it mean to say that a system computes? What distinguishes computing systems, such as brains, from non-computing systems, such as stomachs and tornadoes? I argue that a "structural" approach to computing cannot account for much of the computational work in cognitive neuroscience. Instead, I offer a modeling account, which is a variant of a "semantic" approach. On this modeling account, the key feature of computing is a similarity between the "inner" mathematical relations, defined over the representing states, and "outer" mathematical relations, defined over the represented states.

Changes in the brain during chronic nicotine: from thermodynamics to neuroadaptation

Lecture
Date:
Tuesday, February 17, 2009
Hour: 10:30
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Prof. Henry Lester
|
California Institute of Technology

The Development of Reading Pathways in School Age Children

Lecture
Date:
Thursday, February 12, 2009
Hour: 11:30
Location:
Nella and Leon Benoziyo Building for Brain Research
Dr. Michal Ben-Shachar
|
English Dept and the Gonda Brain Research Center Bar Ilan University

Learning to read involves exposure to large amounts of print in a focused period of time during childhood. How does this environmental transition affect cortical circuits for visual perception and shape recognition? I will present data from a developmental study of reading examining the relation between reading skill, cortical function and white matter properties in school age children. Functional properties in area MT+, and white matter properties in temporal callosal fibers, are both correlated with reading skill. I will discuss possible interpretations of these findings within a general model of the reading pathways.

Plasticity in the Human Ventral Stream:: Regional Differences Across Time Scales

Lecture
Date:
Monday, February 9, 2009
Hour: 12:30
Location:
Arthur and Rochelle Belfer Building for Biomedical Research
Prof. Kalanit Grill-Spector
|
Dept of Psychology & Neurosciences Institute Stanford University, CA

The human ventral stream consists of regions in the lateral and ventral aspects of the occipital and temporal lobes and is involved in visual recognition. One robust characteristic of selectivity in the adult human ventral stream is category selectivity. Category selectivity is manifested by both a regional preference to particular object categories, such as faces, places and bodyparts, as well as in specific (and reproducible) distributed response patterns across the ventral stream for different object categories. However, it is not well understood how experience modifies these representations and how do these representations come about throughout development. Here, I will describe two sets of experiments in which we addressed these important questions. First, I will describe experiments in adults in which we examined the effect of repetition on categorical responses in the ventral stream. Repeating objects decreases responses in the human ventral stream. However, repetition largely does not change the profile of category selectivity in the ventral stream, except for a place-selective region in the collateral sulcus in which long-lagged repetitions sharpened its responses. Second, I will describe experiments in which we examined changes in category selectivity throughout development from middle childhood (7-11 years), through adolescence (12-16) into adulthood. Surprisingly, we find that it takes more than a decade for the development of adult-like face and place-selective regions. In contrast, the lateral occipital object-selective region showed an adult-like profile by age 7. Finally, I will discuss the implications of these results on plasticity in the ventral stream and our theoretical models linking between fMRI measurements and the underlying neural mechanisms.

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