16577Where Does Consciousness Come From?
- Mar 19, 2009Where Does Consciousness Come From?
ScienceDaily (Mar. 17, 2009) Consciousness
arises as an emergent property of the human mind.
Yet basic questions about the precise timing,
location and dynamics of the neural event(s)
allowing conscious access to information are
not clearly and unequivocally determined.
Some neuroscientists have even argued that
consciousness may arise from a single "seat"
in the brain, though the prevailing idea
attributes a more global network property.
Do the neural correlates of consciousness correspond
to late or early brain events following
perception? Do they necessarily involve coherent
activity across different regions of the brain,
or can they be restricted to local patterns of
A new paper suggests that four specific, separate
processes combine as a "signature" of conscious
activity. By studying the neural activity of
people who are presented with two different
types of stimuli one which could be perceived
consciously, and one which could not Dr. Gaillard
of INSERM and colleagues, show that these four
processes occur only in the former, conscious
This new work addresses the neural correlates of
consciousness at an unprecedented resolution,
using intra-cerebral electrophysiological recordings
of neural activity. These challenging experiments
were possible because patients with epilepsy who
were already undergoing medical procedures requiring
implantation of recording electrodes agreed to
participate in the study. The authors presented
them with visually masked and unmasked printed
words, then measured the changes in their brain
activity and the level of awareness of seeing the
words. This method offers a unique opportunity to
measure neural correlates of conscious access with
optimal spatial and temporal resolutions. When
comparing neural activity elicited by masked and
unmasked words, they could isolate four converging
and complementary electrophysiological markers
characterizing conscious access 300 ms after word
All of these measures may provide distinct glimpses
into the same distributed state of long-distance
reverberation. Indeed, it seems to be the convergence
of these measures in a late time window (after 300 ms),
rather than the mere presence of any single one of
them, which best characterizes conscious trials.
"The present work suggests that, rather than hoping
for a putative unique marker the neural correlate
of consciousness a more mature view of conscious
processing should consider that it relates to a
brain-scale distributed pattern of coherent brain
activation," explained neuroscientist Lionel
Naccache, one of the authors of the paper.
The late ignition of a state of long distance
coherence demonstrated here during conscious
access is in line with the Global Workspace
Theory, proposed by Stanislas Dehaene,
Jean-Pierre Changeux, and Lionel Naccache.
1. Gaillard et al. Converging Intracranial
Markers of Conscious Access. PLoS Biology, 2009;
7 (3): e61 DOI: 10.1371/journal.pbio.1000061
Adapted from materials provided by Public Library
of Science, via EurekAlert!, a service of AAAS.
- Next post in topic >>