Investigating neural correlates of conscious perception by frequency-tagged neuromagnetic responses

During binocular rivalry, where each eye sees a different image but only one is consciously perceived at a time, neuromagnetic responses in the brain show activity at frequencies corresponding to both stimuli, even for the unseen one. However, when a stimulus is not consciously perceived, the power of its neural response is reduced by 50-85% across many brain regions, including areas outside the visual cortex. This modulation is widespread but not global, indicating that conscious perception correlates with the strength of synchronized neural activity in large neuronal populations.

Study at a glance

Abstract

In binocular rivalry, a subject views two incongruent stimuli through each eye but consciously perceives only one stimulus at a time, with a switch in perceptual dominance every few seconds. To investigate the neural correlates of perceptual dominance in humans, seven subjects were recorded with a 148-channel magnetoencephalography array while experiencing binocular rivalry. A red vertical grating flickering at one frequency was presented to one eye through a red filter and a blue horizontal grating flickering at a different frequency was presented to the other eye through a blue filter. Steady-state neuromagnetic responses at the two frequencies were used as tags for the two stimuli and analyzed with high-resolution power spectra. It was found that a large number of channels showed peaks at both frequencies, arranged in a horseshoe pattern from posterior to anterior regions, whether or not the subject was consciously perceiving the corresponding stimulus. However, the amount of power at the stimulus frequency was modulated in relation to perceptual dominance, being lower in many channels by 50-85% when the subject was not conscious of that stimulus. Such modulation by perceptual dominance, although not global, was distributed to a large subset of regions showing stimulus-related responses, including regions outside visual cortex. The results demonstrate a correlation between the conscious perception of a visual stimulus and the synchronous activity of large populations of neurons as reflected by steady-state neuromagnetic responses.