Physiological properties of the electrically stimulated auditory nerve. I. Compound action potential recordings.

The electrically evoked compound action potential (CAP) of the auditory nerve exhibits two peaks, termed N0, at 350 microseconds latency, and N1, at 550 microseconds latency. At low stimulus intensities the CAP consists solely of the long latency N1 peak. As the stimulus strength is increased the higher threshold N0 appears. At high stimulus intensities N1 disappears and only the N0 component of the CAP remains. It is postulated that N1 represents action potentials propagated from the dendritic processes of the auditory neurons and that N0 represents action potentials initiated on the axons of these cells. The N1 peak exhibits anomalous refractory behavior which can be identified in the electrically evoked auditory brainstem response (EABR). That behavior may be useful diagnostically in assessing the extent of dendrite degeneration in cochlear implant candidates and users.