SYNAPTIC ORIGIN OF RHYTHMIC VISUALLY EVOKED ACTIVITY IN KITTEN AREA 17 NEURONS

RHYTHMIC patterns in neuronal activity in response to moving stimuli were observed in 28% of cells recorded extracellularly or intracellularly in area 17 of 4-16 week old anaesthetized and paralysed kittens. In both recording modes, oscillation frequencies ranged between 7 and 71 Hz, and were confined for 88% of cells in the 7-20 Hz band of the spectrum. A comparative study of firing autocorrelograms) and subthreshold activity (autocorrelation functions) indicates that the regularity of discharge stemmed from visually evoked oscillations of membrane potential at the same frequency. These oscillations are shown to result from extrinsic excitatory activity, since their amplitude, but not their frequency, depends on the resting membrane potential. The dependency on stimulus configuration supports the hypothesis that oscillations in neuronal output are dictated by periodic activity in afferent circuits selectively recruited by different attributes of the visual input which are not exclusively processed at the cortical level.