October 31, 2007

Dynamic neural correlates of consciousness

EEG, fMRI, neuroimaging, perception — thomasr @ 3:27 am Print This Post  AddThis Social Bookmark Button

PLOS Biology has a most interesting article from Stanislas Dehaene’s group on the neurodynamics of conscious experience. The researchers studied brain activation using EEG, while subjects rated visually presented stimuli on a scale from unseen to clearly seen. It was found that conscious experience of a stimulus was related to the engagement of a widespread network involving the frontal, parietal and temporal cortices.

SCR note: It is mentioning a recent study using fMRI (Christensen et al. 2006) provided comparable results, and adding two factors; (1) the conscious experience of a visual stimulus involved activation of both thalami, and (2) subjects consistently rated some experiences as vague, i.e., as “detected but not identified”. This experience was associated with both lower activation in those regions involved in conscious experience, and unique activation of additional regions, including some prefrontal regions.

Author description: Understanding the neural mechanisms that distinguish between conscious and nonconscious processes is a crucial issue in cognitive neuroscience. In this study, we focused on the transition that causes a visual stimulus to cross the threshold to consciousness, i.e., visibility. We used a backward masking paradigm in which the visibility of a briefly presented stimulus (the “target”) is reduced by a second stimulus (the “mask”) presented shortly after this first stimulus. (Human participants report the visibility of the target.) When the delay between target and mask stimuli exceeds a threshold value, the masked stimulus becomes visible. Below this threshold, it remains nonvisible. During the task, we recorded electric brain activity from the scalp and reconstructed the cortical sources corresponding to this activity. Conscious perception of masked stimuli corresponded to activity in a broadly distributed fronto-parieto-temporal network, occurring from about 300 ms after stimulus presentation. We conclude that this late stage, which could be clearly separated from earlier neural events associated with subliminal processing and mask-target interactions, can be regarded as a marker of consciousness.


  1. This paper from Dehaene’s group gives us additional strong evidence in support of Baar’s Global Workspace theory of consciousness. If the evolutionary benefit of consciousness is to provide us (the human organism) with a global representation of our world to which we must adapt in order to survive and flourish, it must be an internally constructed model of the world from an egocentric perspective. This internal (brain) model must contain all salient features of the world organized in proper spatio-temporal register (accurate feature binding) within a 3D representational system that includes a representaion of the self (the owner of egocentric space) at its spatial origin. This would conform with Revonsuo’s suggestion that our phenomenal experience depends on a brain system which can provide a transparent model of the world from an egocentric perspective. What kind of brain system can give us a transparent model of the world from an egocentric perspective? My claim is that what I have called the *retinoid system* is, in effect, Baar’s Global Workspace. It is a global representational space with widespread output to, and input from all sensory processing modalities in the brain (see Fig.8 in Trehub (2007), Space, self, and the theater of consciousness , *Consciousness and Cognition*). The minimal structural and dynamic properties of its neuronal mechanisms and systems have been detailed in *The Cognitive Brain*.

    Arnold Trehub

    Comment by Arnold Trehub — October 31, 2007 @ 2:41 pm

  2. I see this paper as a confirmation of my TRANS theory (www.ruf.dk/trans2.doc)
    The heart of the TRANS theory is the existence of a “generator loop” binding different aspects together in a complete conscious experience.
    TRANS was presented at the TSC2005 conference in Copenhagen
    Palle R Jensen
    TRANS Institute
    Forhaabningsholms Alle 30, 1904 Frederiksberg C.

    Comment by Palle R Jensen — November 27, 2007 @ 6:06 am

RSS feed for comments on this post. TrackBack URI

Leave a comment

Line and paragraph breaks automatic, e-mail address never displayed, HTML allowed: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>