Figure 3.

Divergent trends in gamma oscillation responses in different areas of visual cortex. (A) Gamma response to a face stimulus in V1 (lower—showing predominantly narrowband gamma power decrease) and in fusiform gyrus (upper—showing broadband gamma power increase) in the same human patient (reproduced with copyright-holder's permission from Lachaux et al., 2005). (B) The effect of selective attention (blue plot = unattended, red/yellow = attended) on gamma power in V1 (upper—showing narrowband gamma decrease) and in V4 (lower—showing gamma increase in a higher broader frequency band; reproduced with copyright-holder's permission from Chalk et al., 2010). (C) Schematic of how above findings can be reconciled if narrowband gamma oscillations are considered an inhibitory process. (i) In response to most basic passively-viewed stimuli, inhibitory narrowband gamma occurs in V1, but onward activity is still conveyed to higher visual areas also triggering gamma oscillations. (ii) In response to explicitly or implicitly attended stimuli, inhibitory narrowband gamma oscillations are reduced, leading to increased onward activity being conveyed to higher visual areas, which in turn triggers stronger gamma responses.