Colour-related oscillations in the striate cortex of awake monkeys: "reverse" observations

Gamma oscillations of 30-70 Hz in local electroencephalograms (EEGs) were observed in primary visual cortex (V1) of monkeys when they viewed coloured stimuli under conditions which were not part of a training paradigm. No oscillatory modulations were detected in simultaneously recorded spike trains, although the latter responded to the stimuli. The oscillations had much longer latencies than the spike responses. Proceeding in a "reverse" manner, the oscillations were taken as primary elements of the analyses, and relationships to the accompanying behaviour were sought. Besides colour stimulation, the oscillations were found to be related to a form of annoyance. Only two of four monkeys showed the phenomena. We conclude that the oscillations had a central origin.