Effects of Stimulus repetition rate on electrically evoked auditory brainstem potentials in postlingually deafened adult Cochlear Implant recipients

The cause of poor speech recognition after cochlear implant (CI) fitting despite good preoperative predictions often cannot be determined. In acoustics, it is known that the auditory brainstem responses (ABR) and their latencies and amplitudes differ with different stimulus rates. Whether this also applies to ectrically evoked compound action potentials (ECAP) and electrically evoked brainstem potentials (EABR) and what the normal values are for different stimulus rates is investigated in this study. Method 20 experienced adult CI users with a good postoperative word recognition score were recruited from the clinic"s patient pool. In the same stimulation mode and intensity we measured latencies and interpeak latencies of EABR and ECAP. With a defined supra-threshold stimulation intensity above the individual ECAP threshold, we applied stimulation at several rates between 11 and 91 stimuli per second. Results We found rate dependencies for EABR latency t3 and t5 in the order of 0.19 ms and 0.37 ms respectively, while ECAP was not affected by rate. Correspondingly, the interpeak intervalls" rate dependence for t5-t1, t5-t3, t3-t1 were in the order of 0.37 ms, 0.18 ms, 0.19 ms. Comparing EABR amplitudes between the stimulation rates 11/s and 81/s, we found that at 81/s the amplitudes were significantly reduced down: to 73% for A3, 81% for A5. These rate dependencies of latency and amplitude in EABR have characteristics comparable to those of acoustic ABR.Conclusions These data may serve to provide reference values for EABR and ECAP latencies, interpeak intervals and amplitudes with respect to stimulus rates. Altered response patterns of ECAP and EABR to normalised stimulation modes could be used in the future to better describe and classify neuropathological processes.