Psychobiology of Altered States of Consciousness Dieter Vaitl University of Giessen Niels Birbaumer University of Tu ¨bingen and University of Trento John Gruzelier and Graham A. Jamieson Imperial College London Boris Kotchoubey and Andrea Ku ¨bler University of Tu ¨bingen Dietrich Lehmann University Hospital of Psychiatry Wolfgang H. R. Miltner University of Jena Ulrich Ott University of Giessen Peter Pu ¨tz Institute for Frontier Areas of Psychology and Mental Health Gebhard Sammer University of Giessen Inge Strauch University of Zurich Ute Strehl University of Tu ¨bingen Jiri Wackermann Institute for Frontier Areas of Psychology and Mental Health Thomas Weiss University of Jena The article reviews the current knowledge regarding altered states of consciousness (ASC) (a) occurring spontaneously, (b) evoked by physical and physiological stimulation, (c) induced by psychological means, and (d) caused by diseases. The emphasis is laid on psychological and neurobiological ap- proaches. The phenomenological analysis of the multiple ASC resulted in 4 dimensions by which they can be characterized: activation, awareness span, self-awareness, and sensory dynamics. The neurophys- iological approach revealed that the different states of consciousness are mainly brought about by a compromised brain structure, transient changes in brain dynamics (disconnectivity), and neurochemical and metabolic processes. Besides these severe alterations, environmental stimuli, mental practices, and techniques of self-control can also temporarily alter brain functioning and conscious experience. Consciousness has come under renewed scientific investigation, with respect to both the various levels of consciousness and the content of consciousness, through advances in the models and methods of cognitive neuroscience (for a review, see Gazzaniga, 2000; Mesulam, 2000; Zeman, 2001). Everyday conscious aware- ness is but the tip of an iceberg, underneath which there is a realm Dieter Vaitl, Center for Psychobiology and Behavioral Medicine and Department of Psychology, University of Giessen, Giessen, Germany; Niels Birbaumer, Institute of Medical Psychology and Behavioral Neuro- biology, University of Tu ¨bingen, Tu ¨bingen, Germany, and Center for Cognitive Neuroscience, University of Trento, Trento, Italy; John Gruze- lier and Graham A. Jamieson, Department of Neuroscience and Psycho- logical Medicine, Imperial College London, London, United Kingdom; Boris Kotchoubey, Andrea Ku ¨bler, and Ute Strehl, Institute of Medical Psychology and Behavioral Neurobiology, University of Tu ¨bingen; Di- etrich Lehmann, The KEY Institute for Brain–Mind Research, University Hospital of Psychiatry, Zurich, Switzerland; Wolfgang H. R. Miltner and Thomas Weiss, Department of Biological and Clinical Psychology, Uni- versity of Jena, Jena, Germany; Ulrich Ott and Gebhard Sammer, Center for Psychobiology and Behavioral Medicine, University of Giessen; Peter Pu ¨tz and Jiri Wackermann, Department of Empirical and Analytical Psy- chophysics, Institute for Frontier Areas of Psychology and Mental Health, Freiburg, Germany; Inge Strauch, Department of Clinical Psychology, University of Zurich, Zurich, Switzerland. This work was supported by the Institute for Frontier Areas of Psychol- ogy and Mental Health, Freiburg, Germany. The Altered States of Con- sciousness (ASC) Consortium, founded in 1998, was devoted to the neu- rophysiological, psychological, and behavioral components of altered states of consciousness. Several psychophysiological laboratories partici- pated in this endeavor and exchanged their results, ideas, and concepts at four consecutive special symposia held in Sils-Maria, Switzerland, from 1999 to 2002. Correspondence concerning this article should be addressed to Dieter Vaitl, Clinical and Physiological Psychology, Department of Psychology, University of Giessen, Otto-Behaghel-Str 10, D-35394, Giessen, Germany. E-mail: dieter.vaitl@psychol.uni-giessen.de Psychological Bulletin Copyright 2005 by the American Psychological Association 2005, Vol. 131, No. 1, 98 –127 0033-2909/05/$12.00 DOI: 10.1037/0033-2909.131.1.98 98