High-frequency oscillations in human visual cortex do not mirror retinal frequencies.

Flash stimulation elicits oscillatory responses above 100 Hz in human visual cortex. It has been proposed that these are the result of retinal oscillations being directly relayed through the visual pathway to area V1. Experimental evidence, however, is scarce and contradictory. To address this issue, we performed a time-frequency analysis of simultaneously recorded retinal and cortical potentials. Matching frequencies would support the assumption of a direct relationship between retinal and cortical activities. In 4 of 7 subjects the frequency was significantly lower in the cortex than in the retina and in one subject it was significantly higher. The differences were in the range of 10-34 Hz and suggest that the cortical oscillations are not a simple echo of their retinal counterparts.