Stimulus dependence of gamma oscillations

Gamma oscillations induced in the visual cortex are highly dependent on the properties of the visual stimulus, such as its size, spatial frequency, contrast etc. We study how gamma power and centre frequency changes as the stimulus properties are modified, and from that try to understand the properties of the underlying network. For example, we found that presenting large (full screen) gratings induces two gamma oscillations, one between 40-70 Hz (“fast gamma”) that appears to be involved in local processing and a slower gamma between 25-40 Hz that is more global (Dinavahi, Shirhatti, Ravishankar* and Ray, Journal of Neuroscience, 2018; * indicates joint authorship). Similarly, We found that gamma rhythm is highly colour tuned, such that presentation of long wavelength (red-ish) hues generate gamma rhythm of very large magnitude (Shirhatti and Ray, 2018, PNAS).