Brett Foster
Department of Neurosurgery
University of Pennsylvania

Limits on the functional role of gamma oscillations in visual perception

Neocortical ‘gamma oscillations’ have repeatedly been proposed as a mechanism of visual perception, and cognition more generally, by coordinating neural activity within and between brain areas. Historically, non-human primate electrophysiology has reported narrowband gamma oscillations (30-70 Hz) within early visual cortex in response to commonly used visual stimuli (e.g. gratings). However, growing evidence suggests that visual gamma oscillations are highly stimulus dependent, and when present, lack critical attributes for supporting perceptual processing and information transfer. We sought to examine these stimulus dependencies directly in human visual cortex via clinical intracranial recordings. Our findings provide robust replication and extension of gamma response stimulus dependences reported in the non-human primate, relating to the structure, color and size of stimuli. Importantly, these findings dissociate classical ‘gamma oscillations’ from commonly reported ‘high gamma’ (70-200 Hz) activity. While suggesting important constraints on the potential for gamma oscillations to coordinate neural circuits supporting visual perception, these finding open up new avenues for considering the functional significance of gamma and oscillations more generally. Importantly, this includes a host of well characterized empirical findings parametrically linking stimuli to gamma response features (i.e., amplitude and frequency) that are ripe for computational examination.

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