[The activity of hippocampal neurons during several types of behavior]

The activity of 87 hippocampal units and the EEG (field CAI) were studied in unrestrained rabbits during calm and active alertness and at different stages of sleep. Correlation has been established between the characteristics (mean frequency and the pattern) of unit firing, EEG and the animal's activity. For most of the neurones, fixed values of mean frequency and the discharge pattern corresponded to a definite functional state. With transition from sleep to alertness, 63.6% of the units became active, 29.1% were inhibited, and the rest of the units changed the firing pattern only. The cells which became activated during awakening, showed a reduced firing frequency during a more profound sleep and higher discharge frequency during the paradoxal phase of sleep, while the inhibitory cells revealed reverse dynamics of discharge frequency. In a state of alertness, the most pronounced shifts in firing activity were observed in 33.3% of the nerve cells at orienting investigating behaviour, in 27.1%, during attention reaction, in 22.9% at some kinds of movement, and in 16.7%, in the course of feeding and drinking. A conclusion has been drawn that the role of the hippocampus in achieving different behavioral reactions is probably to a great extent determined by its participation in setting up a level of the brain central tone, specific for each state.