Antagonistic relationship between gamma power and visual evoked potentials revealed in human visual cortex

Scalp electroencephalography and magnetoencephalography studies have revealed a rapid evoked potential "adaptation" where one visual stimulus suppresses the event-related potential (ERP) of the second stimulus. Here, we investigated a similar effect revealed in subdural intracranial recordings in humans. Our results show that the suppression of the subdural ERP is not associated with a reduction in the gamma frequency power, considered to reflect the underlying neural activity. Furthermore, the evoked potential suppression (EPS) phenomenon was not reflected in recognition behavior of the patients. Rather, the EPS was tightly linked to the level of gamma activity preceding the event, and this effect was independent of the interstimulus time interval. Analyzing other frequency bands failed to reveal a similar link. Our results thus show a consistent antagonism between subdural ERP and gamma power although both are considered markers for neural activity. We hypothesize that the ERP suppression is due to a desynchronization of neuronal firing resulting from recurrent neural activity in the vicinity of the freshly stimulated neurons and not an attenuation of the overall neural activity.