Electrographic studies on the nature of sleep and wakefulness

Abstract

Electroencephalographic activity of the neocortical gyri, ventral hippocampus, caudate nucleus and reticular formation (diencephalon to medulla) and other regions was investigated during natural sleep-wakefulness cycles spread over 88 sessions in 34 cats, free moving with implanted electrodes. The electrooculgram and the electromyogram of neck nuchal muscles were simultaneously recorded and correlated with the behavior. Regional EEG cycles differed in 4 ways: (a) those with synchronized EEG throughout the sleep and wakefulness, as in the ventral hippocampus, (b) those with desynchronised activity throughout, as in the bulbo-pontine reticular formation, (c) those with desynchronized EEG during wakefulness and active sleep and synchronized patterns during slow sleep, as in the neocortical gyri, caudate nucleus and near by regions, and (d) those that follow the pattern of (c) with slow waves superimposed, as in the mesencephalic reticular formation. Low voltage, low frequency stimulations given to the area lateral to the massa intermedia, nucleus reticularis pontis caudalis, nucleus reticularis ventralis, optic chiasma and the sciatic nerve induced EEG synchronization occasionally, but never an active sleep. A region more dynamogenic than the other diencephatic and reticular areas explored, was observed near the nucleus tractus trigemini. In view of the observations that the activation of restricted hypnogenic centres did not consistently produce somnolence and that the EEG changes during natural sleep-wakefulness cycles are simultaneous in the different regions and involve almost the whole structure of the brain, it is discussed that the involved integratory networks are likely to be much more extensive including the hypnogenic and the dynamogenic regions investigated here.