Influence of feedback signals from Cats ara 21a on contrast response function of Area 17 neurons

Feedback signals originating from cats extrastriate visual cortices exert mostly excitatory influence on neuronal responses in area 17 (A17). In the present study we found that feedback signals from one of the form-processing extrastriate cortical areas, area 21a (A21a), modulate the contrast response function of A17 neurons. Thus, in a majority (13/18) of A17 cells examined there was a significant change in contrast response function during inactivation of A21a. While the magnitude of the responses to stimulus contrasts tends to decrease during inactivation of A21a there was no systematic change in the mid-contrast, i.e. the contrast at which the response of individual neurons reached 50 of its maximum response. Further analysis indicated that the effect on the magnitude of responses was stronger at high contrast. These results suggest that an overall excitatory feedback from A21a may play a role in enhancing contrast response in A17 neurons, especially at high contrast.