STEADY POTENTIAL CHANGES DURING CORTICAL ACTIVATION

Abstract

Slow potential changes accompany-ing cortical activation were studied in the rabbit and cat. In the rabbit activation was produced by sciatic nerve and midbrain tegmental stimulation; in the cat by intravenous epinephrine (7 /[mu]g/kg). Animals were prepared under ether, immobilized (Flaxedil) [gallamine triethio-dide] and carried with artificial respiration. Sciatic- and midbrain-induced activation was examined before and during deepening barbiturate anesthesia. To produce epinephrine activation a background of re-current eeg and spindling produced by acute lesions of the caudal midbrain RF was necessary. Records were obtained with non-polariz-able electrodes and dc amplifier from frontal granular (rabbit) and anterior suprasylvian cortex (cat). A diphasic (neg./pos.) slow potential (SP) shift accompanies activation produced by all methods mentioned above. In an already activated trace (midbrain or sciatic stimulation) no eeg change is evident, the SP shift occurring alone. In the spindle stage of barbiturate anesthesia activation is produced easily and small amplitude, cortical transients appear variably upon 10/second tegmental stimulation. With further increments of the anesthetic agent, activation and the associated SP shift are blocked together. Additional barbiturate injection leads to an iso-electric trace and a much enlarged response comes to follow a single tegmental stimulus. At I/second repetitive stimulation these transients show a marked amplitude decrement past the 1st response. The findings are related to the graded response theory of cortical dendritic activation.