Recovery from monocular deprivation using binocular deprivation: Experimental observations and theoretical analysis.

Blais B, Frenkel M, Kuindersma S, Muhammad R, Shouval HZ, Cooper LN, Bear MF.
J Neurophysiol. 2008 Jul 23.

Ocular dominance (OD) plasticity is a robust paradigm for examining the functional consequences of synaptic plasticity. Previous experimental and theoretical results have shown that OD plasticity can be accounted for by known synaptic plasticity mechanisms, using the assumption that deprivation by lid suture eliminates spatial structure in the deprived channel. Here we show that in the mouse, recovery from monocular lid suture can be obtained by subsequent binocular lid suture but not by dark rearing. This poses a significant challenge to previous theoretical results. We therefore performed simulations with a natural input environment appropriate for mouse visual cortex. In contrast to previous work we assume that lid suture causes degradation but not elimination of spatial structure, whereas dark rearing produces elimination of spatial structure. We present experimental evidence that supports this assumption, measuring responses through sutured lids in the mouse. The change in assumptions about the input environment is sufficient to account for new experimental observations, while still accounting for previous experimental results.

PMID: 1865031

Full text: http://jn.physiology.org/cgi/reprint/90411.2008v1

Students and Professors

Spatio-temporal correlations and visual signalling in a complete neuronal population

Pillow JW, Shlens J, Paninski L, Sher A, Litke AM, Chichilnisky EJ, Simoncelli EP.
Nature. 2008 Jul 23.

Statistical dependencies in the responses of sensory neurons govern both the amount of stimulus information conveyed and the means by which downstream neurons can extract it. Although a variety of measurements indicate the existence of such dependencies, their origin and importance for neural coding are poorly understood. Here we analyse the functional significance of correlated firing in a complete population of macaque parasol retinal ganglion cells using a model of multi-neuron spike responses. The model, with parameters fit directly to physiological data, simultaneously captures both the stimulus dependence and detailed spatio-temporal correlations in population responses, and provides two insights into the structure of the neural code. First, neural encoding at the population level is less noisy than one would expect from the variability of individual neurons: spike times are more precise, and can be predicted more accurately when the spiking of neighbouring neurons is taken into account. Second, correlations provide additional sensory information: optimal, model-based decoding that exploits the response correlation structure extracts 20% more information about the visual scene than decoding under the assumption of independence, and preserves 40% more visual information than optimal linear decoding. This model-based approach reveals the role of correlated activity in the retinal coding of visual stimuli, and provides a general framework for understanding the importance of correlated activity in populations of neurons.

PMID: 18650810

Fulltext: http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature07140.pdf

Spatio-temporal correlations and visual signalling in a complete neuronal population

Pillow JW, Shlens J, Paninski L, Sher A, Litke AM, Chichilnisky EJ, Simoncelli EP.
Nature. 2008 Jul 23.

Statistical dependencies in the responses of sensory neurons govern both the amount of stimulus information conveyed and the means by which downstream neurons can extract it. Although a variety of measurements indicate the existence of such dependencies, their origin and importance for neural coding are poorly understood. Here we analyse the functional significance of correlated firing in a complete population of macaque parasol retinal ganglion cells using a model of multi-neuron spike responses. The model, with parameters fit directly to physiological data, simultaneously captures both the stimulus dependence and detailed spatio-temporal correlations in population responses, and provides two insights into the structure of the neural code. First, neural encoding at the population level is less noisy than one would expect from the variability of individual neurons: spike times are more precise, and can be predicted more accurately when the spiking of neighbouring neurons is taken into account. Second, correlations provide additional sensory information: optimal, model-based decoding that exploits the response correlation structure extracts 20% more information about the visual scene than decoding under the assumption of independence, and preserves 40% more visual information than optimal linear decoding. This model-based approach reveals the role of correlated activity in the retinal coding of visual stimuli, and provides a general framework for understanding the importance of correlated activity in populations of neurons.

PMID: 18650810

Fulltext: http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature07140.pdf

Highly Selective Receptive Fields in Mouse Visual Cortex

Cristopher M. Niell and Michael P. Stryker
The Journal of Neuroscience, July 23, 2008 • 28(30):7520 –7536

Genetic methods available in mice are likely to be powerful tools in dissecting cortical circuits. However, the visual cortex, in which
sensory coding has been most thoroughly studied in other species, has essentially been neglected in mice perhaps because of their poor
spatial acuity and the lack of columnar organization such as orientation maps.Wehave now applied quantitative methods to characterize
visual receptive fields in mouse primary visual cortex V1 by making extracellular recordings with silicon electrode arrays in anesthetized
mice.Weused current source density analysis to determine laminar location and spike waveforms to discriminate putative excitatory and
inhibitory units.Wefind that, although the spatial scale of mouse receptive fields is up to one or two orders of magnitude larger, neurons
show selectivity for stimulus parameters such as orientation and spatial frequency that is near to that found in other species. Furthermore,
typical response properties such as linear versus nonlinear spatial summation (i.e., simple and complex cells) and contrastinvariant
tuning are also present in mouse V1 and correlate with laminar position and cell type. Interestingly, we find that putative
inhibitory neurons generally have less selective, and nonlinear, responses. This quantitative description of receptive field properties
should facilitate the use of mouse visual cortex as a system to address longstanding questions of visual neuroscience and cortical
processing.

Free Fulltext: http://www.jneurosci.org/cgi/reprint/28/30/7520

Brain Magic

Patches of face-selective cortex in the macaque frontal lobe.

Tsao DY, Schweers N, Moeller S, Freiwald WA.
Nat Neurosci. 2008 Jul 11.

In primates, specialized occipital-temporal face areas support the visual analysis of faces, but it is unclear whether similarly specialized areas exist in the frontal lobe. Using functional magnetic resonance imaging in alert macaques, we identified three discrete regions of highly face-selective cortex in ventral prefrontal cortex, one of which was strongly lateralized to the right hemisphere. These prefrontal face patches may constitute dedicated modules for retrieving and responding to facial information.

PMID: 18622399

Fulltext: http://www.nature.com/neuro/journal/vaop/ncurrent/abs/nn.2158.html

Acetylcholine contributes through muscarinic receptors to attentional modulation in V1.

Herrero JL, Roberts MJ, Delicato LS, Gieselmann MA, Dayan P, Thiele A.
Nature. 2008 Jul 16.

Attention exerts a strong influence over neuronal processing in cortical areas. It selectively increases firing rates and affects tuning properties, including changing receptive field locations and sizes. Although these effects are well studied, their cellular mechanisms are poorly understood. To study the cellular mechanisms, we combined iontophoretic pharmacological analysis of cholinergic receptors with single cell recordings in V1 while rhesus macaque monkeys (Macaca mulatta) performed a task that demanded top-down spatial attention. Attending to the receptive field of the V1 neuron under study caused an increase in firing rates. Here we show that this attentional modulation was enhanced by low doses of acetylcholine. Furthermore, applying the muscarinic antagonist scopolamine reduced attentional modulation, whereas the nicotinic antagonist mecamylamine had no systematic effect. These results demonstrate that muscarinic cholinergic mechanisms play a central part in mediating the effects of attention in V1.

PMID: 18633352

Fulltext: http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature07141.pdf

Functional Differentiation of Macaque Visual Temporal Cortical Neurons Using a Parametric Action Space.

Vangeneugden J, Pollick F, Vogels R.
Cereb Cortex. 2008 Jul 16.

Neurons in the rostral superior temporal sulcus (STS) are responsive to displays of body movements. We employed a parametric action space to determine how similarities among actions are represented by visual temporal neurons and how form and motion information contributes to their responses. The stimulus space consisted of a stick-plus-point-light figure performing arm actions and their blends. Multidimensional scaling showed that the responses of temporal neurons represented the ordinal similarity between these actions. Further tests distinguished neurons responding equally strongly to static presentations and to actions ("snapshot" neurons), from those responding much less strongly to static presentations, but responding well when motion was present ("motion" neurons). The "motion" neurons were predominantly found in the upper bank/fundus of the STS, and "snapshot" neurons in the lower bank of the STS and inferior temporal convexity. Most "motion" neurons showed strong response modulation during the course of an action, thus responding to action kinematics. "Motion" neurons displayed a greater average selectivity for these simple arm actions than did "snapshot" neurons. We suggest that the "motion" neurons code for visual kinematics, whereas the "snapshot" neurons code for form/posture, and that both can contribute to action recognition, in agreement with computation models of action recognition.

PMID: 18632741

Free Fulltext: http://cercor.oxfordjournals.org/cgi/content/full/bhn109v1

Distinct Face-Processing Strategies in Parents of Autistic Children

Adolphs R, Spezio ML, Parlier M, Piven J.
Curr Biol. 2008 Jul 15.

In his original description of autism, Kanner [1] noted that the parents of autistic children often exhibited unusual social behavior themselves, consistent with what we now know about the high heritability of autism [2]. We investigated this so-called Broad Autism Phenotype in the parents of children with autism, who themselves did not receive a diagnosis of any psychiatric illness. Building on recent quantifications of social cognition in autism [3], we investigated face processing by using the "bubbles" method [4] to measure how viewers make use of information from specific facial features in order to judge emotions. Parents of autistic children who were assessed as socially aloof (N = 15), a key component of the phenotype [5], showed a remarkable reduction in processing the eye region in faces, together with enhanced processing of the mouth, compared to a control group of parents of neurotypical children (N = 20), as well as to nonaloof parents of autistic children (N = 27, whose pattern of face processing was intermediate). The pattern of face processing seen in the Broad Autism Phenotype showed striking similarities to that previously reported to occur in autism [3] and for the first time provides a window into the endophenotype that may result from a subset of the genes that contribute to social cognition.

PMID: 18635351

Fulltext: Science Direct

Modulation of neural responses in inferotemporal cortex during the interpretation of ambiguous photographs.

Liu Y, Jagadeesh B.
Eur J Neurosci. 2008 Jun;27(11):3059-73.

Ambiguous images are interpreted in the context of biases about what they might be; these biases and the behavioral consequences induced by them may influence the processing of images. In this report, we examine neural responses in inferotemporal cortex (IT) during the interpretation of ambiguous photographs created by morphing between two photographs. Monkeys classified different images as being one of two choices and learned to classify most of the samples correctly. For one image (the ambiguous sample) reward was administered randomly for either possible choice, and the monkeys were free to classify that image based on their own interpretation, with no learning possible. The ambiguous samples were not classified randomly: the monkey interpreted the samples differently during different sessions. The interpretation of the ambiguous sample was, in turn, highly correlated with the normalized response of individual neurons in IT to the ambiguous sample. If an ambiguous sample was interpreted as a particular choice during a session, the response to that ambiguous sample more closely resembled the response to that choice. Identical ambiguous images were interpreted differently during different sessions, and neural responses reflected the differing interpretations of the image during that session. The relationship between the interpretation of the image and neural responses strengthened over the course of a session because neural responses shifted to more closely resemble the response to the initial interpretation of the image. The data support a flexible representation of visual stimuli in higher visual areas.

PMID: 18588544