Pii: S0010-0277(00)00123-2

This introductory chapter attempts to clarify the philosophical, empirical, and theoretical bases on which a cognitive neuroscience approach to consciousness can be founded. We isolate three major empirical observations that any theory of consciousness should incorporate, namely (1) a considerable amount of processing is possible without consciousness, (2) attention is a prerequisite of consciousness, and (3) consciousness is required for some speci®c cognitive tasks, including those that require durable information maintenance, novel combinations of operations, or the spontaneous generation of intentional behavior. We then propose a theoretical framework that synthesizes those facts: the hypothesis of a global neuronal workspace. This framework postulates that, at any given time, many modular cerebral networks are active in parallel and process information in an unconscious manner. An information becomes conscious, however, if the neural population that represents it is mobilized by top-down attentional ampli®cation into a brain-scale state of coherent activity that involves many neurons distributed throughout the brain. The long-distance connectivity of these `workspace neurons' can, when they are active for a minimal duration, make the information available to a variety of processes including perceptual categorization, longterm memorization, evaluation, and intentional action. We postulate that this global availability of information through the workspace is what we subjectively experience as a conscious state. A complete theory of consciousness should explain why some cognitive and cerebral representations can be permanently or temporarily inaccessible to consciousness, what is the range of possible conscious contents, how they map onto speci®c cerebral circuits, and whether a generic neuronal mechanism underlies all of them. We confront the workspace model with those issues and identify novel experimental predictions. Neurophysiological, anatomical, and brain-imaging data strongly argue for a major role of prefrontal cortex, S. Dehaene, L. Naccache / Cognition 79 (2001) 1±37 1 Cognition 79 (2001) 1±37 www.elsevier.com/locate/cognit 0010-0277/01/$ see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0010-0277(00)00123-2 COGN I T I O N * Corresponding author. Tel.: 133-1-69-86-78-73; fax: 133-1-69-86-78-16. E-mail address: [email protected] (S. Dehaene). anterior cingulate, and the areas that connect to them, in creating the postulated brain-scale workspace. q 2001 Elsevier Science B.V. All rights reserved.