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

Gamma oscillations of 30-70 Hz in local electroencephalograms (EEGs) were o bserved in primary visual cortex (V1) of monkeys when they viewed coloured stimuli under conditions which were not part of a training paradigm. No osc illatory modulations were detected in simultaneously recorded spike trains, although the latter responded to the stimuli. The oscillations had much lo nger latencies than the spike responses. Proceeding in a "reverse" manner, the oscillations were taken as primary elements of the analyses, and relati onships to the accompanying behaviour were sought. Besides colour stimulati on, 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.