Brain Physiology, Cognition and Consciousness: notice board entry
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The 300ms Wave
- Posted by:
- Alfredo Pereira Jr (group admin)
- Date:
- 19 October 2007
- Comments:
- 2 comments
(From Science’s Editors’ Choice of Recent Literature)
NEUROSCIENCE: Too Quick to Glimpse?
Katrina L. Kelner
An optical illusion can help define which parts of the brain are
responsible for human consciousness. People cannot consciously
perceive a
number flashed on a screen for 16 ms if it is quickly followed by
another
stimulus in the same area. As the time between the two stimuli
increases,
the first stimulus becomes visible; that is, it is accessible to the
person’s consciousness. Del Cul et al. recorded electrical brain
waves from people’s scalps as they were shown these stimuli and
reported to
the investigators whether they were visible or invisible. One brain
wave in
particular, P3, occurring 270 to 400 ms after the beginning of the
trial,
correlated with conscious perception of the stimulus. This wave
seems to
arise from sudden simultaneous activity in several parts of the brain,
specifically the frontal, parietal, and temporal cortices of both
hemispheres. These data are inconsistent with several proposed
correlates
of consciousness, including the rapid induced activity in the visual
areas
of the brain and the later more distributed, but still local, neural
reverberations. Rather, they suggest that conscious perception is
associated with a sudden global reverberation of neural activity,
about 300
ms after the stimulus, encompassing several cortical areas
bilaterally.
PLoS Biol. 5, 10.1371/journal.pbio.0050260 (2007).
When I published this notice, the paper was not freely available. Now you can get the PDF here
The Abstract is pasted below:
PLoS Biol. 2007 Oct;5(10):e260.
Brain dynamics underlying the nonlinear threshold for access to consciousness.
Del Cul A, Baillet S, Dehaene S.
INSERM, Cognitive Neuroimaging Unit, IFR 49, Saclay, France.
antoine.delcul@cea.fr
When a flashed stimulus is followed by a backward mask, subjects fail to perceive
it unless the target-mask interval exceeds a threshold duration of about 50 ms.
Models of conscious access postulate that this threshold is associated with the
time needed to establish sustained activity in recurrent cortical loops, but the
brain areas involved and their timing remain debated. We used high-density
recordings of event-related potentials (ERPs) and cortical source reconstruction
to assess the time course of human brain activity evoked by masked stimuli and to
determine neural events during which brain activity correlates with conscious
reports. Target-mask stimulus onset asynchrony (SOA) was varied in small steps,
allowing us to ask which ERP events show the characteristic nonlinear dependence
with SOA seen in subjective and objective reports. The results separate distinct
stages in mask-target interactions, indicating that a considerable amount of
subliminal processing can occur early on in the occipito-temporal pathway (270 ms) and highly distributed
fronto-parieto-temporal activation as a correlate of conscious reportability.
PMCID: PMC1988856
PMID: 17896866 [PubMed – indexed for MEDLINE]
I´ve just posted a review of this paper for our relative, Nature Network´s Neuroscience group
Best
Alfredo