Local Circuits & Direction Selectivity in Visual Cortex

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DESCRIPTION (From the Applicant's Abstract): This project proposes using the techniques of optical imaging and single unit recording to analyse the substrates for direction specificity in primary visual cortex of the ferret. The issue raised is that the various aspects of single moving objects present conflicting cues as to the direction of its motion (e.g. as illustrated by motion of contours in an aperture, or the barber pole illusion).Yet the visual system resolves these differences to predict an overall direction of motion and an accurate guide to eye movements. The proposed studies examine in detail the neuron population responses in V1 (by optical imaging) to movement of both oriented contour motion and the terminations of the same contour (which may be equated with dot motion). The experiments test the hypothesis that the perceived direction of motion is a weighted sum of the responses to the different directions of motion present in the stimulus. This sum can be affected by length of contour, contrast and speed. Single unit recording will be used to test the properties of single neurons at different points in the optical maps, to verify the map predictions, to test for variability of responses at single points, to test spatial interactions between terminal point and contour driven activity, and, together with voltage sensitive dye imaging, to examine differences in temporal evolution of signals from terminators and contours.