Aix Marseille Univ, CNRS, Centrale Marseille, LMA, 4 Impasse Nikola Tesla, CS 40006, 13453 Marseille Cedex 13, France.
Aix Marseille Univ, CNRS, Centrale Marseille, LMA, 4 Impasse Nikola Tesla, CS 40006, 13453 Marseille Cedex 13, France.
Hear Res. 2021 Apr;403:108176. doi: 10.1016/j.heares.2021.108176. Epub 2021 Jan 22.
While electrically-evoked auditory brainstem response (eABR) thresholds for low-rate pulse trains correlate well with behavioral thresholds measured at the same rate, the correlation is much weaker with behavioral thresholds measured at high rates, such as used clinically. This implies that eABRs to low-rate stimuli cannot be reliably used for objective programming of threshold levels in cochlear implant (CI) users. Here, we investigate whether the use of bunched-up pulses (BUPS), consisting of groups of closely-spaced pulses may be used as an alternative stimulus. Experiment 1 measured psychophysical detection thresholds for several stimuli having a period of 32 ms in nine CI subjects implanted with a Med-EL device. The stimuli differed in the number of pulses present in each period (from 1 to 32), the pulse rate within period (1000 pps and as high as possible for BUPS) and the electrode location (apical or basal). The correlation between psychophysical thresholds obtained for a high-rate (1000 pps) clinical stimulus and for the BUPS stimuli increased as the number of pulses per period of BUPS increased from 1 to 32. This first psychophysical experiment suggests that the temporal processes affecting the threshold of clinical stimuli are also present for BUPS. Experiment 2 measured eABRs on the apical electrode of eight CI subjects for BUPS having 1, 2, 4, 8, 16 or 32 pulses per period. For most subjects, wave V was visible for BUPS having up to 16 pulses per period. The latency of wave V at threshold increased as a function of the number of pulses per period, suggesting that the eABR reflects the integration of multiple pulses at such low levels or that the neural response to each individual pulse increases along the sequence due to facilitation processes. There was also a strong within-subject correlation between electrophysiological and behavioral thresholds for the different BUPS stimuli. This demonstrates that the drop in behavioral threshold obtained when increasing the number of pulses per period of the BUPS can be measured electrophysiologically using eABRs. In contrast, the across-subject correlation between eABR thresholds for BUPS and clinical thresholds remained relatively weak and did not increase with the number of pulses per period. Implications of the use of BUPS for objective programming of CIs are discussed.
当低频脉冲串的电诱发听觉脑干反应 (eABR) 阈值与以相同速率测量的行为阈值密切相关时，与以较高速率（如临床上使用的速率）测量的行为阈值的相关性要弱得多。这意味着，对于低频刺激的 eABR 不能可靠地用于耳蜗植入 (CI) 用户的阈值水平的客观编程。在这里，我们研究了使用簇状脉冲 (BUPS) 是否可以作为替代刺激。实验 1 在 9 名植入 Med-EL 设备的 CI 受试者中测量了几种具有 32ms 周期的刺激的心理物理检测阈值。刺激在每个周期中存在的脉冲数（从 1 到 32）、周期内的脉冲率（1000pps 和尽可能高的 BUPS）以及电极位置（顶端或基底）方面有所不同。对于高率（1000pps）临床刺激获得的心理物理阈值与 BUPS 刺激之间的相关性随着每个 BUPS 周期的脉冲数从 1 增加到 32 而增加。这项首次心理物理实验表明，影响临床刺激阈值的时间过程也存在于 BUPS 中。实验 2 在 8 名 CI 受试者的顶端电极上测量了 BUPS 的 eABR，BUPS 每个周期有 1、2、4、8、16 或 32 个脉冲。对于大多数受试者，每个周期有 16 个脉冲以下的 BUPS 可观察到波 V。随着每个周期的脉冲数的增加，波 V 的潜伏期也随之增加，这表明 eABR 反映了在如此低的水平下对多个脉冲的整合，或者由于易化过程，每个单独脉冲的神经反应沿着序列增加。对于不同的 BUPS 刺激，电生理和行为阈值之间也存在很强的个体内相关性。这表明，当每个周期的 BUPS 脉冲数增加时，行为阈值的下降可以通过 eABR 进行电生理测量。相比之下，BUPS 的 eABR 阈值与临床阈值之间的个体间相关性仍然相对较弱，并且不会随每个周期的脉冲数的增加而增加。讨论了使用 BUPS 进行 CI 的客观编程的意义。
