Spectral Signatures of Feedforward and Recurrent Circuitry in Monkey Area MT

Abstract

Recordings of local field potential (LFP) in the visual cortex can showrhythmic activity at gammafrequencies (30-100 Hz). While the gammarhythms in the primary visual cortex have beenwell studied, the structural and functional characteristics of gamma rhythms in extrastriate visual cortex are less clear. Here,we studied the spatial distribution and functional specificity of gamma rhythms in extrastriate middle temporal (MT) area of visual cortex in marmoset monkeys. We found that moving gratings induced narrowband gamma rhythms across cortical layers that were coherent across much of area MT. Moving dot fields instead induced a broadband increase in LFP in middle and upper layers, with weaker narrowband gamma rhythms in deeper layers. The stimulus dependence of LFP response in middle and upper layers of areaMTappears to reflect the presence (gratings) or absence (dot fields and other textures) of strongly oriented contours. Our results suggest that gamma rhythms in these layers are propagated from earlier visual cortex, while those in the deeper layers may emerge in area MT.