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J Neurophysiol 102: 1241-1253, 2009. First published June 10, 2009; doi:10.1152/jn.91044.2008
0022-3077/09 $8.00
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Spectral Properties of Induced and Evoked Gamma Oscillations in Human Early Visual Cortex to Moving and Stationary Stimuli

J. B. Swettenham, S. D. Muthukumaraswamy and K. D. Singh

Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, United Kingdom

Submitted 18 September 2008; accepted in final form 7 June 2009

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 ~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.

Address for reprint requests and other correspondence: K. D. Singh, Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Park Place, Cardiff CF10 3AT, UK (E-mail: singhkd{at}cardiff.ac.uk)






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