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| Exploring the Global Workspace of Consciousness |
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| SciMed - Neuroscience | ||||||
| Richard Robinson | ||||||
| Wednesday, 18 March 2009 16:00 | ||||||
 San Francisco, CA, USA. As an explanatory principle in biology, vitalism has long been in decline, as one discovery after another revealed that mechanisms provide convincing explanations — hearts are pumps, genes are code — for all manner of life's phenomena. [N1] But even through the 20th century, the mind has been vitalism's last redoubt, because there has been no simple, satisfactory, mechanistic explanation of the most puzzling aspect of the mind: the nature of conscious awareness. For many years, even asking questions about the inner workings of this mental black box was taboo among some groups of scientists.
But that has all changed. A flood of new discoveries in every area of
 neuroscience has led to competing models of consciousness, and most importantly, testable hypotheses. A new study by Raphael Gaillard, Lionel Naccache, and colleagues provides support for one such model by showing that conscious, but not nonconscious, visual information is rapidly and widely distributed across the brain, provoking the synchronized brain activity that is the hallmark of conscious processing. [N2]Seattle, WA, USA. A new dataset in the Allen Brain Atlas shows good conservation of gene expression between humans and mice, with reports of some striking differences.
A report published in the journal Cell examines the cell...
That, according to the model, is what we experience as consciousness.
A difficulty of consciousness studies is that humans are the best subjects, but probing inside their brains purely for research purposes is unethical. So the authors turned to patients with medically intractable epilepsy, who, in preparation for surgery, had required multiple shallow recording electrodes to be implanted within their cerebral cortexes to locate seizure activity.
The authors showed the participants a computer screen, upon which they projected first a set of hatch marks (acting as a meaningless “mask”), then a word, and then either a blank screen or a set of ampersands (another mask). The entire sequence took only half a second, and the word was flashed so briefly that in neither case could the participant name the word. But in both cases the word was registered at the earliest stages of visual processing nonetheless, as shown by electrical activity in the primary visual cortex, thus meeting the first condition of the global workspace model.
The words themselves were either of a threatening (“kill,” “danger”) or nonthreatening (“cousin,” “see”) nature. When participants were exposed to words followed by the second mask, they could guess the nature of the words they saw with no better than chance frequency. The second stage was not reached; the fire was doused before it could ignite.
But when the second mask was absent, the words were consciously reportable and readable, so the authors could compare masked (nonconscious) perception and unmasked (conscious) perception of briefly flashed words.
The electrodes told the same story. There were sustained voltage changes throughout the brain, especially in the prefrontal cortex. The voltage changes were accompanied by an increase in power within specific brain wave frequencies associated with cognitive processing, as well as synchronization of activity among many different brain regions — in short, the brain gave every appearance of thinking about the word.
In the language of the global workspace model, the stimulus endured long enough, and gained enough attention, to be promoted to the workspace, at which point information about it was broadcast throughout the brain to be processed in multiple ways — including the determination of its emotional character.
The authors point out that consciousness is always “about” something; there may be no “pure” state of consciousness that is independent of the content of our thought, and so an important question is whether these results, concerning a single word the participant could not even name, are generalizable to understanding the ongoing flow of our conscious experience. Further experiments with other kinds of stimuli may reveal which late-stage, widespread brain events are common to all conscious processing, and which are specific to the experiment at hand.
Notes [N1] Vitalism is a doctrine a long history in medical philosophies that supposes the functions of a living organism as due to a vital principle distinct from biochemical reactions. In this view, life's processes of are not explicable by the laws of physics and chemistry alone: life is in some part self-determining. The vital principle is often referred to as the "vital spark" or "élan vital," which some equate with the "soul."
[N2] Converging intracranial markers of conscious access. Raphaël Gaillard, Stanislas Dehaene, Claude Adam, Stéphane Clémenceau, Dominique Hasboun, Michel Baulac, Laurent Cohen, Lionel Naccache. PLoS Biology 7(3): e61. doi: 10.1371/journal.pbio.1000061. Download PDF The research is discussed in a companion TS-Si.org article: What Gives Rise To Our Consciousness? TS-Si News Service TS-Si.org (18 March 2009) Citation Exploring the “Global Workspace” of Consciousness. Richard Robinson (2009) PLoS Biology 7(3): e1000066. doi: 10.1371/journal.pbio.1000066
Article concurently published with PLoS Biology. Copyright: © 2009 Richard Robinson. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.  Richard Robinson is a publication assistant with PLoS Biology. The TS-Si News Service is a collaborative effort by TS-Si.org editors, contributors, and corresponding institutions. Sources can include the cited individuals and organizations, as well as TS-Si.org staff contributions. Articles and news reports do not necessarily convey official positions of TS-Si, its partners, or affiliates. We welcome your comments. Use the form below to leave a public comment or send private correspondence via the TS-Si Contact Page. We will not divulge any personal details or place you on a mailing list without your permission.TS-Si is dedicated to the acceptance, medical treatment, and legal protection of individuals correcting the misalignment of their brains and their anatomical sex, while supporting their transition into society as hormonally reconstituted and surgically corrected citizens.
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