EVOKED RESISTANCE SHIFTS IN UNANESTHETIZED CATS

A new phenomenon, the evoked resistance shift (ERS) that is time-locked to the sensory evoked potential (EP), was studied in cats with chronically implanted electrodes. The ERS disappeared at nearly all cerebellar vermis and cerebral cortical electrode sites shortly after implantation but persisted for times up to several months at subcortical nuclei. In the auditory system, the ERS magnitude and capacity for functional recovery (response to increased stimulus repetition rate) varied, being smallest at medial geniculate and largest at medullary nuclei (cochlear nucleus, superior olive). Barbiturate anesthesia failed to alter the subcortical ERS after auditory or visual stimulation. The data demonstrate that brain regions differ in respect to ERS size, stability, sensitivity to drugs and trauma, and capacity for functional recovery. They also show that the events responsible for the electrical EP are not identical with those responsible for the ERS. © 1968.