Temporal correlations between heart rate, medullary units and hippocampal theta rhythm in anesthetized, sleeping and awake guinea pigs

The aim of the present report was to determine whether or not the heart rate could show any relation to a central electrographic rhythm such as hippocampus theta. Our experimental design included anesthetized as well as chronically implanted guinea pigs. The cross-correlation, spike trigger averaging, between the medullary neurons firing, or the R-wave of the electrocardiogram, or hippocampal units, and theta rhythm revealed phase-locking during epochs of wakefulness, slow wave sleep and paradoxical sleep, and under anesthesia. A special case was paradoxical sleep, an epoch known to lack autonomic function control (open-loop), in which a great majority of the recorded units (83%) exhibited theta phase-locking. The experimental control was a flat cross-correlation after unit firing shuffling. A brain-stem autonomic oscillator, together with a hypothalamic and a cortico-frontal centers entrained by baroreceptor input, have been proposed as the heart rhythm control system. The present report suggests that hippocampal theta waves may participate, in coordination with the hypothalamic center, as a heart rate modulator.