Converging intracranial markers of conscious access

PLoS Biol. 2009 Mar 17;7(3):e61. doi: 10.1371/journal.pbio.1000061.

Abstract

We compared conscious and nonconscious processing of briefly flashed words using a visual masking procedure while recording intracranial electroencephalogram (iEEG) in ten patients. Nonconscious processing of masked words was observed in multiple cortical areas, mostly within an early time window (<300 ms), accompanied by induced gamma-band activity, but without coherent long-distance neural activity, suggesting a quickly dissipating feedforward wave. In contrast, conscious processing of unmasked words was characterized by the convergence of four distinct neurophysiological markers: sustained voltage changes, particularly in prefrontal cortex, large increases in spectral power in the gamma band, increases in long-distance phase synchrony in the beta range, and increases in long-range Granger causality. We argue that all of those measures provide distinct windows into the same distributed state of conscious processing. These results have a direct impact on current theoretical discussions concerning the neural correlates of conscious access.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Brain Mapping
  • Cerebral Cortex / physiology*
  • Consciousness / physiology*
  • Electroencephalography / methods*
  • Epilepsy
  • Humans
  • Male
  • Middle Aged
  • Neurophysiology
  • Perceptual Masking / physiology
  • Visual Perception / physiology
  • Young Adult