Abstract:
Altered states of consciousness (ASC) are difficult to define and previous attempts to do so have not been widely adopted. This is a problem inherent in defining consciousness in general. Theories that link ASC to neural substrates, such as the transient hypofrontality theory, promise to alleviate this situation. Drug-induced alterations to conscious experience also seem to defy definition and classification but they can be understood in terms of classes of psychoactive drugs and common phenomenology. The brain, in response to psychoactive compounds, seems to alter conscious experience in predictable and quantifiable ways. © 2009 Elsevier Inc. All rights reserved.