Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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BCCN Sonderseminar

Wednesday, 09.07.2008 15 c.t.

Temporal decorrelation of evoked oscillatory responses in primary visual cortex

by Dr. Demian Battaglia
from University Paris Descartes

Contact person: Theo Geisel

Location

Seminarraum Haus 2, 4. Stock (Bunsenstr.)

Abstract

In primary visual cortex, nearby neurons respond preferentially to oriented stimuli, presented within classical receptive fields of similar position, and share similar orientation tuning properties. While monosynaptic inhibition tends to be confined within the columnar scale, the lateral spread of excitatory connections can be as large as several millimeters (2-6 mm). Many studies have reported the existence of patchy horizontal excitatory projections linking preferentially distant neurons that respond to collinear stimuli. Thus, an intra-striatal excitatory coupling between neurons in distinct columns is established and the resulting interaction is likely to provide a contribution to context-dependent extra-classical receptive field effects. We study here simple firing-rate and conductance-based models of two V1 hypercolumns interacting via lateral orientation-selective long-range excitation. Each hypercolumn is modeled by a simplified tridimensional network, that takes in account the existence of multiple coupled cortical layers receiving an input from LGN. The connectivity is random and the probabilities of excitatory and inhibitory connections within the hypercolumn depend on the relative layer localizations and preferred orientations of the interconnected neurons. The excitatory neurons in addition can also establish connections toward excitatory or inhibitory neurons in the distant hypercolumn, with a probability that decays quickly with the difference between the pre- and post-synaptic preferred orientations. In presence of a tuned input, localized oscillatory responses are generated in each hypercolumn via local mutual inhibitory interactions. These evoked oscillations undergo a fast temporal decorrelation because of the predominantly excitatory interactions between the cortical layers, in agreement with theoretical predictions of simplified models (Battaglia, Brunel and Hansel, PRL 2007). An additional stimulus-dependent contribution to the temporal decorrelation of evoked oscillations can be observed when stimuli of different relative orientation are presented simultaneously in the receptive fields associated to the two hypercolumns. Our theory of long-range excitation-induced temporal decorrelation of cortical oscillations predicts that the decorrelation time of the evoked oscillatory responses in these simultaneously activated interacting receptive fields will be modulated by the relative orientation of the presented bars (faster decorrelation for collinear stimuli, even in presence of a stronger istantaneous synchronization). To conclude, we speculate about possible functional implications of the illustrated dynamical mechanisms.

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