The degree of orientation selectivity of neurons in V1 depends on the local orientation map

Abstract

Single-unit studies of primary visual cortex (V1) have revealed a wide diversity in the degree to which neurons are tuned for stimulus orientation. This tuning diversity may be accounted for by the distribution of orientation preferences of nearby cells. For example, if V1 neurons excite each other, than neurons near pinwheel centers should have a broader tuning width than neurons in orientation domains where nearby cells have similar orientation preferences. To test this hypothesis, we obtained a map of orientation preference in macaque and cat V1 using optical imaging. We then implanted an electrode array (10×10; 400mm separation) in the same patch of cortex to record the activity at multiple locations in the map. The electrophysiological and optical measurements yielded similar measures of orientation preference, allowing us to localize our electrodes in the map with high precision. We then measured the orientation tuning bandwidth of the neurons recorded with the electrode array, and found that cells in regions of the map near pinwheel centers are more broadly tuned than cells in iso-orientation domains. These results suggest that tuning in V1 neurons is influenced by the distribution of preferred orientations in the local neighborhood.