In the mid-1990s, Professors Stanislas Dehaene and Jean-Pierre Changeux devised a theoretical and experimental approach that would enable them to understand the biological processes entailed in Man’s access to consciousness. Through their work, these two pioneers in Neuroscience have been able to objectively measure neural activity related to how we consciously process information. Today, the two researchers publish a review of fifteen years of theoretical and experimental work in Neuron.

To measure neural activity at the moment of entering consciousness, the researchers developed an experimental model based on a simple idea: a comparison of cerebral activity under conditions imitating the conscious or non-conscious processing of information. Thus, written words are thus briefly shown to a subject amid a series of images. From one test to another, by varying the conditions under which these images were presented, the subject is either able or unable to report the written word. If the person is able to report the word, then conscious processing has come into play. If this is not the case, it means the word has not been consciously perceived. It can nonetheless be shown that the word has in fact been processed by the brain, subliminally, or non-consciously. For each of these experimental situations, neural activity is measured in a number of different regions of the subject’s brain, using various brain imaging techniques. It is thus possible to objectively compare the different neural activities entailed in conscious processing and in non-conscious processing of the same visual stimulus.

Pursuing this research using fast recording methods to record electrical activity in the brain has helped to establish the sequence of events that unfurls in the brain when accessing consciousness. The first areas of the brain to be activated, regardless of whether information is processed consciously or non-consciously, are in the visual cortex, especially those areas involved in the recognition of written words. During conscious processing, about 200 to 400 milliseconds after being shown the word, a huge electrical wave sweeps through a vast brain network that includes the prefrontal cortex. According to the researchers, this network is synchronized when entering into consciousness thanks to neurons densely interconnected by long-range axons.

It is this latter step that, according to Stanislas Dehaene and Jean-Pierre Changeux, marks the access to consciousness. They uphold the idea that this firing up of the prefrontal network and the synchronization of neural activity in these areas can only be triggered if a minimum threshold of activity is reached during the preceding steps. Conscious processing would thus be akin to making information available within a “neuronal workspace”, allowing the signal to reach the long-term memory.

Jean-Pierre Changeux and Stanislas Dehaene’s theories will help interpret various clinical situations in which access to consciousness is altered or impeded, for example, under general anesthetic, in a coma or in psychiatric illnesses such as schizophrenia.

Publication of this review of the researchers’ work in the prestigious journal, Neuron, is a sign of the scientific community’s recognition of their research. Nonetheless, the consciousness access model proposed should, according to the authors themselves, be seen simply as a first model of human consciousness: given the current incredible advances in Neuroscience, it is bound to evolve and become more precise.

Source

Experimental and Theoretical Approaches to Conscious Processing, Neuron, April 28, 2011.

Stanislas Dehaene (1,2,3,4) & Jean-Pierre Changeux (4,5) DOI 10.1016/j.neuron.2011.03.018

(1) INSERM, Cognitive Neuroimaging Unit, Gif sur Yvette, 91191 France

(2) CEA, DSV, I2BM, Neurospin Center, Gif sur Yvette, 91191 France

(3) University Paris 11, Orsay 91401, France

(4) Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France

(5) Institut Pasteur CNRS URA 2182, Institut Pasteur, 75015 Paris, France