From the electrophysiological and vegetative and behavioural points of view (Jouv~,T, 1962) sleep in mammals is characterized by the cyclic alternation of two different phases. Sleep begins with slow wave EEG activity generalised over the whole brain (the telencephalic or slow wave sleep phase); this is followed by the rhombencephalie or paradoxical sleep phase, characterized by regular theta activity in the hippocampus and desynchronisation of the eorticogram appearing after a transitory period of cortical spindling.
The very high frequency of sleep cycles (MICH~,L et al., 1961 ; ROLI)X~ and WEISS, 1962; SOVLAmAC and GOTTESMA~N, 1963) and the fact that rats sleep during the day make it possible to collect a statistically sufficient amount of data in these animals with relative case. Rats are therefore suitable for work on the pharmacology of sleep cycles. The following report is part of a study dealing with this problem.
One relevant pharmacological question is the action of various hypnotic drugs on sleep and to what extent sleep induced by a drug may be regarded as physiological. For this purpose the influence of thiopcntal on the sleep cycle has been investigated.