Introduction

Abstract

The concept that sleep and waking are controlled by some chemical change dates back to the early 1900s: Legender and Piéron [1] showed that infusion into subarachnoidal spaces of liquor cerebrospinalis, total brain extract and serum from a ten-day sleep deprived dog to another dog induced a behavioral sleep in the latter. They suggested the existence of ‘hypnotoxins’ responsible for that sleep. In 1927, Hess [2] induced sleep in the cat by electrical stimulation of the ventral thalamus, near to the commissura interthalamica. His criteria of normal sleep in the cat were suppression of spontaneus contact with environment while intact arousal reactivity to external auditory, olfactory and tactile stimuli remained, constriction of the pupil, closure of the nictating membrane and of the eyelids, typical sleep posture.