The use of long-duration current pulses to assess nerve survival.

This study investigated the usefulness of long-duration current pulses in assessing the status of the auditory nerve in ears with various degrees of retrograde neural degeneration. Guinea pigs were deafened with aminoglycosides prior to acute implantation of the cochlea and collection of electrically evoked auditory brainstem responses (EABRs). Analysis of wave I evoked with long-duration current pulses suggests that this evoked response is sensitive to degeneration of the peripheral processes of the auditory nerve. Correlations with spiral ganglion cell density show that EABR measures obtained with long-duration pulses are comparable to those previously established for estimating nerve survival. Further analysis indicates that this measure may provide unique information about the degenerative state of the nerve. Threshold EABR measures using long-duration pulses are evidently more place-specific than other measures. Also, results suggest that long-duration pulses may be sensitive to two phases of the degenerative process: degradation of the peripheral processes and subsequent degeneration of neural processes central to the spiral ganglion.