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Dajun Xing, Chun-I Yeh, Patrick Williams, Andy Henrie, Robert Shapley; Image discontinuity changes LFP gamma-band activity in primary visual cortex V1. Journal of Vision 2009;9(8):753. doi: 10.1167/9.8.753.
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© ARVO (1962-2015); The Authors (2016-present)
In V1 cortex, large continuous visual stimuli suppress neurons' firing rates and power in the local field potential (LFP) spectrum [[gt]] 70 Hz. However, the spectral peak of LFP power in the gamma-band (around 50 Hz) often increases with stimulus size (Bauer et al., 1995; Henrie et al., 2006). This differential effect of stimulus size on the gamma-band peak could be explained if 1) gamma-band activity represents local neuronal activity, which is more synchronized by large stimuli (Gail et al., 2000) or 2) gamma-band activity represents neuronal activity in a large area of the cortex and grows stronger when more V1 neurons are activated by large stimuli. To decide between 1 and 2, we studied LFP responses to visual stimuli with or without spatial discontinuities.
LFPs were recorded in response to a large-area (8 deg radius) sinusoidal grating centered on receptive fields of neurons at the recording site. We also measured gamma-band coherence between different recording sites. Spatial continuity of the grating pattern was broken by an annulus of mean gray. Annulus inner diameter was around 1 deg. The gap between the outer and inner annulus radii ranged from 0.05 to 0.2 deg. To measure how much gamma-band power was evoked from the receptive field periphery, LFPs were recorded when the central disk region was blank.
A small visual gap of width 0.1deg greatly reduced LFP power at 50Hz for half of the recording sites (20/50) and gamma-band coherence also could be affected by image discontinuity. Furthermore, the amount of gamma-band activity evoked by annuli with inner diameters [[gt]] 1 deg was always small. Our results indicate that gamma-band activity in the LFP is a signal mainly from the local cortex and that image discontinuity can change the pattern of gamma-band activity.
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