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In two experiments, magnetoencephalography (MEG) was used to investigate the effects of motion on gamma oscillations in human early visual cortex. When presented centrally, but not peripherally, stationary and moving gratings elicited several evoked and induced response components in early visual cortex. Time-frequency analysis revealed two nonphase locked gamma power increases-an initial, rapidly adapting response and one sustained throughout stimulus presentation and varying in frequency across observers from 28 to 64 Hz. Stimulus motion raised the sustained gamma oscillation frequency by a mean of approximately 10 Hz. The largest motion-induced frequency increases were in those observers with the lowest gamma response frequencies for stationary stimuli, suggesting a possible saturation mechanism. Moderate gamma amplitude increases to moving versus stationary stimuli were also observed but were not correlated with the magnitude of the frequency increase. At the same site in visual cortex, sustained alpha/beta power reductions and an onset evoked response were observed, but these effects did not change significantly with the presence of motion and did not correlate with the magnitude of gamma power changes. These findings suggest that early visual areas encode moving and stationary percepts via activity at higher and lower gamma frequencies, respectively.

Original publication

DOI

10.1152/jn.91044.2008

Type

Journal article

Journal

Journal of Neurophysiology

Publication Date

08/2009

Volume

102

Pages

1241 - 1253

Addresses

Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff CF10 3AT, United Kingdom.

Keywords

Visual Cortex, Humans, Magnetoencephalography, Brain Mapping, Photic Stimulation, Visual Perception, Motion Perception, Periodicity, Evoked Potentials, Visual, Time Factors, Adult, Female, Male, Young Adult