Electrically and acoustically evoked brain stem responses in guinea pig.

Brain stem evoked responses (BSERs) to acoustic and electrical stimulations of the cochlea were compared in guinea pigs. The electric stimuli evoked an averaged response of five to six successive waves within 10 msec, which was similar to that elicited by acoustic stimuli, though the latency of the electrical response was markedly shorter. Moreover, direct electrical stimulation of the auditory nerve evoked the same pattern of response as that elicited by electrical stimulation of the cochlea. On the other hand, stimulation of the vestibular nerve evoked a distinctly different pattern of response that lasted at most for 1.5 msec. Facial nerve stimulation evoked no brain stem response by this procedure. These results suggest that the waves of longer latency over 1.5 msec are available as indicators of auditory activity, even if the response elicited by electrical stimulation of the cochlea might be the sum of auditory and vestibular activities.