Converging intracranial markers of conscious access.
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.
Gaillard
Raphaël
R
INSERM, Cognitive Neuro-Imaging Unit, Institut Fédé ratif de Recherche (IFR) 49, Gif sur Yvette, France.
Dehaene
Stanislas
S
Adam
Claude
C
Clémenceau
Stéphane
S
Hasboun
Dominique
D
Baulac
Michel
M
Cohen
Laurent
L
Naccache
Lionel
L
D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology*; D003243:Consciousness / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods*; D004827:Epilepsy; D006801:Humans; D008297:Male; D008875:Middle Aged; D009482:Neurophysiology; D010470:Perceptual Masking / Q000502:physiology; D014796:Visual Perception / Q000502:physiology; D055815:Young Adult