Hypothalamic and cortical D-C potential changes induced by stimulation of the midbrain reticular formation.

Abstract

D-C potential changes were evoked in the sensorimotor cortex and the hypothalamus of unanesthetized cats with chronically implanted electrodes by repetitive stimulation of the mesencephalic reticular formation. Stimulation at 30 to 300 p/sec. frequencies induced negative d-c shifts which were quite abrupt in onset, starting after the second or third shock with a peak of negativity reached within the first 50 to 100 msec of the 1 second duration of stimulation. Typically these negative shifts were sustained for the duration of stimulation with a prolonged 1 to 1.5 second return to baseline after termination of stimulation. Such d-c shifts were relatively independent of the site of the reference electrode but highly dependent on the location of the “active” recording electrodes and the stimulating electrodes. Reasons have been advanced to suggest that these negative d-c shifts reflect summated neuronal discharge in the immediate environs of “active” recording electrodes in the cerebral cortex and hypothalamus. In contrast to the consistent, stimulus-locked negative d-c shifts, less consistent changes, usually positive in polarity, were observed to begin 2 to 3 seconds after termination of RF stimulation. These slower d-c changes were highly dependent on the site of the reference electrode and the physical state of tissue at the electrode tip and therefore far less directly related to neuronal events in cortical and hypothalamic tissue.