Second Psychophysiological Study of
Out-of-the-Body Exp...

Relaxed alertness is accompanied in many people by the alpha rhythm, a rather regular, sinusoidal rhythm whose frequency varies from about 8 to 13 cps, although in a single person the frequency is relatively constant. As a person becomes drowsy, this alpha rhythm breaks up, clusters of it becoming less and less frequent as they are replaced by a stage- 1 drowsy pattern. Consciousness waxes and wanes with the alpha rhythm, although it is impossible to say clearly at exactly what point consciousness is lost.

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