Bernstein Center Freiburg

PhD Seminar

August 6, 2019
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Bernstein Seminar
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Bernstein Center Freiburg | University of Freiburg

Orientation selectivity emerging from randomly sampling the visual field

Tuesday, August 6, 2019

17:15h

Hosted by Marco Tabarelli

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Bernstein Center Freiburg
Lecture Hall (ground floor)
Hansastr. 9a
79104 Freiburg


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Abstract

Selectivity for the orientation (OS) of moving gratings is also observed in the primary visual cortex (V1) of species which lack an orientation map, like mice and rats. However, the mechanism underlying the emergence of orientation selectivity in V1 is still mysterious. In the visual pathway, the signals from the retina are conveyed to V1 via relay cells in the lateral geniculate nucleus (LGN). We suggest a computational model of orientation processing in LGN and V1, where orientation selectivity emerges from random thalamo-cortical connectivity and investigate the underlying neuronal mechanism. Firstly we show that the temporal mean (F0) of the thalamic input does not depend on orientation, while the amplitude of the temporal modulations (F1) induced by the grating is indeed tuned to stimulus orientation. The orientation bias in the thalamic F1 can be transformed into orientation tuning of mean firing rate of V1 neurons by an inhibition-dominated random network, exploiting the nonlinear input-output function of individual neurons. The untuned excitatory component is largely cancelled by the inhibitory component, such that the operating point is stabilized in the nonlinear regime of the transfer function. In addition, the orientation preference of a V1 neuron is sensitive to the spatial frequency of the visual stimulus, very similar to what is found in neuronal recordings.

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