ULTRADIAN RHYTHM IN THE DELTA-FREQUENCY AND THETA-FREQUENCY BANDS OF THE EEG IN THE POSTERIOR HYPOTHALAMUS OF THE RAT

The EEG signal of the area hypothalami posterior (PH) was recorded in the urethane anaesthetized rat. The main characteristic of the EEG in this brain region was intermittent oscillations of high amplitude in t he delta and theta frequency bands. Oscillations of the alpha and beta frequency bands showed comparatively lower variations. Time distribut ion analysis of the EEG spectral power revealed that the delta and the ta rhythms appeared and disappeared according to an ultradian rhythm w ith a frequency of approximately 1 cycle per 100 min. No significant r hythm was found in the alpha and beta band. The rhythm frequency of ne uronal activity in the PH is very similar to the ultradian frequency o f pulsatile neurotransmitter release in the PH demonstrated previously .