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CMB Monday Seminar - Farran Briggs

Apr 19, 2010
from 04:00 PM to 05:30 PM

267 Cousteau Place, Large Conference Room

Temporal dynamics of surround suppression in two distinct neuronal populations

Neurons in the early visual system respond in a selective manner to stimuli that vary in size.  Optimal stimuli presented within the classical receptive field of a neuron illicit excitatory responses.  For many early visual neurons, stimuli that extend beyond the classical receptive field into extra-classical surround regions evoke suppressive responses.  Such neurons are said to display surround suppression.  Surround suppression in retinal ganglion cells and thalamocortical relay neurons can be described spatially by a difference-of-Gaussians model.  In these neurons, the temporal onset of excitation is similar to that of suppression.  Since surround suppression is present in retinal and thalamic neurons, it is hypothesized that a large component of cortical surround suppression is generated by feedforward mechanisms.  We recorded from two distinct populations of complex neurons in layer 6 of primary visual cortex.  While both populations displayed similar tuning to drifting sine-wave gratings varying in size and both displayed similar magnitudes of surround suppression, the temporal dynamics of suppression differed across the two cell types.  In order to test whether the mechanisms generating suppression differed between these neuronal classes, we created a modified energy model for complex neurons in V1 in which we varied both the spatial receptive field kernels as well as the time constants defining the temporal kernels.  I will be presented preliminary data generated from the model in support of the notion that different mechanisms contribute to surround suppression in the two neuronal types studied.

 

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