A concept of consciousness.

The term "consciousness", so widely used in clinical settings, is considered extremely complex and practically undefinable. Historically, consciousness was ignored by the great classical philosophers, and was regarded as a basic condition of "being". This changed with Descartes and during the ensuing centuries. A simplified, reductionistic and easily definable concept of consciousness is proposed; consciousness is proposed to consist of three main components: vigilance, mental contents, and selective attention. These three components can be investigated with modern neuroscientific methods--vigilance being the most readily explorable function. The striking differences between sleep and coma are pointed out (along with some observations on sleep initiation). Special attention is paid to epileptic impairment of consciousness and, in particular, to the spike-wave absence which is thought to be due to a temporary suspension of the "working memory circuits" within the frontal lobe.