Visual cortical gamma-band activity during free viewing of natural images

Cereb Cortex. 2015 Apr;25(4):918-26. doi: 10.1093/cercor/bht280. Epub 2013 Oct 9.


Gamma-band activity in visual cortex has been implicated in several cognitive operations, like perceptual grouping and attentional selection. So far, it has been studied primarily under well-controlled visual fixation conditions and using well-controlled stimuli, like isolated bars or patches of grating. If gamma-band activity is to subserve its purported functions outside of the laboratory, it should be present during natural viewing conditions. We recorded neuronal activity with a 252-channel electrocorticographic (ECoG) grid covering large parts of the left hemisphere of 2 macaque monkeys, while they freely viewed natural images. We found that natural viewing led to pronounced gamma-band activity in the visual cortex. In area V1, gamma-band activity during natural viewing showed a clear spectral peak indicative of oscillatory activity between 50 and 80 Hz and was highly significant for each of 65 natural images. Across the ECoG grid, gamma-band activity during natural viewing was present over most of the recorded visual cortex and absent over most remaining cortex. After saccades, the gamma peak frequency slid down to 30-40 Hz at around 80 ms postsaccade, after which the sustained 50- to 80-Hz gamma-band activity resumed. We propose that gamma-band activity plays an important role during natural viewing.

Keywords: ECoG; free viewing; gamma; natural image; oscillation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Electrocorticography
  • Electrodes, Implanted
  • Gamma Rhythm*
  • Macaca
  • Male
  • Photic Stimulation
  • Saccades / physiology
  • Visual Cortex / physiology*
  • Visual Perception / physiology*