Defining the states of consciousness

Consciousness remains an elusive concept due to the difficulty to define wh at has been regarded for many years as a subjective experience, therefore i rrelevant for scientific study. Recent development in this field of researc h has allowed to provide some new insight to a possible way to define consc iousness. Going through the extensive literature in this domain, several pe rspectives are proposed to define this concept. (1) Consciousness and Atten tion may not reflect the same process. (2) Consciousness during wake and sl eep may not involve the same mechanisms. (3) Besides physiological states o f consciousness, human beings can experience modified states of consciousne ss either by self-training (transcendent al meditation, hypnosis, etc.) or by drug intake (hallucinogens, anaesthetics, etc.). Altogether, we address the question of a more precise terminology, given the theoretical weight wo rds can convey. To this respect, we propose different definitions for conce pts Like consciousness, vigilance, arousal and alertness as candidates to s eparate functional entities. (C) 2001 Elsevier Science Ltd. All rights rese rved.