Ultradian rhythm in the delta 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 the delta and theta frequency bands. Oscillations of the alpha and beta frequency bands showed comparatively lower variations. Time distribution analysis of the EEG spectral power revealed that the delta and theta rhythms appeared and disappeared according to an ultradian rhythm with a frequency of approximately 1 cycle per 100 min. No significant rhythm was found in the alpha and beta band. The rhythm frequency of neuronal activity in the PH is very similar to the ultradian frequency of pulsatile neurotransmitter release in the PH demonstrated previously.