Contour decouples gamma activity across texture representation in monkey striate cortex.

Previous work on figure-ground coding in monkey V1 revealed enhanced spike rates within an object's surface representation, synchronization of gamma oscillations (gamma = 35-90 Hz) in object and background regions, but no decrease in signal correlation across the representation of a contour. The latter observation seems to contradict previous statements on the role of gamma-synchronization for scene segmentation. We re-examine these findings by analyzing different coupling measures and frequency ranges of population activities potentially contributing to figure-ground segregation. Multiple unit activity (MUA) and local field potentials (LFPs) were recorded by parallel mu-electrodes in monkey V1 during stimulation by a grating in which an object was defined by a shifted rectangle. In contradiction to the conclusions in previous work, we find strong decoupling of population activity between figure and ground representations compared to the situation in which the object is absent. In particular, coherence of late gamma-LFPs is strongly reduced, while reduction is absent during the early epochs of high-amplitude transients for LFP- and MUA-coherence at all frequencies, and at low frequencies also in the subsequent epochs. Our results of decoupling in late LFP gamma-components among figure and ground representations suggest that these signals may support figure-ground segregation.