Hippocampal rhythmic slow activity (RSA) during animal hypnosis in the rabbit.

Hippocampal electrical activity has been studied in 12 unanaesthetized, unrestrained rabbits during hypnosis and spontaneous activity in the experimental cage, before and among hypnosis trials. Quantitative analyses showed that rhythmic slow activity (RSA) occurred during exploratory movements (mean frequency 7.2 Hz) and also during spontaneous immobility, but a lower percentage and frequency (6.5 Hz). RSA was always present during the induction of hypnosis, but its frequency decreased and disappeared at the beginning of immobility, when it was replaced by a large amplitude irregular activity (LIA). During hypnosis RSA occurred in short periods, at low frequency (5.7 Hz). During the initial part of hypnosis, the lowest percentage of RSA was recorded. In the sec ond and third part, RSA increased in number of episodes, total amount, duration of a single episode and mean frequency. RSA of higher frequency occurred at the end of hypnosis, preceding righting movements. The relationships between hippocampal RSA and animal hypnosis are discussed.