EEG and multiple-unit activity in limbic and motor systems during movement and immobility

Abstract

Electrographic activity was recorded from chronically implanted electrodes generally in the caudate nucleus, septum, hippocampus, and midbrain and medullary levels of the brain stem reticular formation (BSRF) of rabbits in order to assess the effects of movements and immobility. Hippocampal theta rhythms were triggered during movements of any sort or during phasic increases in muscle electrical activity. Coinciding with or preceding the theta onset were phasic increases of multiple-unit activity in the BSRF. Injection of tranquilizer simultaneously reduced movements, abolished theta rhythm, and selectively depressed BSRF units. These specific electrographic correlates of muscle activity were not observed in the caudate, septum, or other telencephalic brain structures from which recordings were derived. Transient theta and increased BSRF activity also occurred during the immobility reflex (animal hypnosis) when the tonic muscle relaxation and immobility were phasically interrupted by mild sensory stimulation. The motor-associated phasic increases in BSRF multiple-unit activity were superimposed upon a tonic unit activity increase in the medullary reticular formation, not seen elsewhere, that was characteristic of the reflex.