AUDITORIALLY EVOKED RESPONSES: A Tool for Assessing the Patient's Ability to Hear during Various States of Consciousness

Relatively little is known about the alteration of hearing with drug-induced changes in consciousness. An objective technique has been devised, and tested in laboratory animals, which records auditorily evoked potentials either from the exposed cerebral cortex or by means of indwelling brain electrodes. New electronic summating techniques now make it possible to record minute electrical potentials directly from the intact scalp of man. While such responses are easy to record for the visual and somatosensory systems, since cortical portions of these systems are located immediately beneath the calvarium and scalp, the human primary auditory cortex is not directly in contact with the parieto-temporal calvarium. Therefore, electronic summating techniques using scalp electrodes may be less effective for auditory stimuli. However, some electrical potentials in response to auditory clicks can consistently be recorded from the human scalp. There is considerable disagreement among clinical neurophysiologists as to whether these responses are cerebral in origin or possibly are scalp-muscle artifacts. The purpose of this study is to shed some light on this controversial issue by studying this phenomenon in anesthetized patients, paralyzed with succinylcholine.