Clay Kelly M Schmidt, Brown Carolyn J
Department of Speech Pathology and Audiology, WJSHC, University of Iowa, Iowa City, Iowa 52242, USA.
Ear Hear. 2007 Dec;28(6):850-61. doi: 10.1097/AUD.0b013e318157671f.
This study had three main goals. The first goal was to assess the extent to which neural adaptation varied across cochlear implant users. The second goal was to determine whether adaptation at the level of the auditory nerve was correlated with word recognition ability. The third goal was to determine whether peripheral neural adaptation had an impact on the relationship between the electrically evoked compound action potential (ECAP) thresholds and MAP levels.
Neural response telemetry software was used to record the ECAP in 21 Nucleus cochlear implant users. A series of 110 ECAP recordings were made over a 5-min period at three different stimulation rates: 15, 80, and 300 Hz. The stimulation levels used to record this series of responses were held constant at or near the level the subject identified as his or her maximum comfort level (C-level) for the 300-Hz stimulation rate. Consistent decreases in ECAP amplitude as measured from the beginning to the end of the 5-min stimulation interval were interpreted as evidence of neural adaptation. Regression analysis procedures were then used to assess the relationship between neural adaptation and word recognition.
Significant levels of adaptation were observed for all 21 subjects at stimulation rates of 80 and 300 Hz. Little or no adaptation was observed over the 5-min recording period when the 15-Hz rate was used. The amount of adaptation was greatest at the 300-Hz rate and varied substantially across cochlear implant users. No relationship between the amount of adaptation and word recognition was found. Neither was the degree of adaptation shown to influence the relationship between ECAP thresholds recorded at low rates and the levels used to program the speech processor.
Cochlear implant users experienced varying degrees of long-term adaptation in response to continuous electrical stimulation. The effects of adaptation on the ECAP were apparent even at stimulation rates as low as 80 Hz. Although variations in the amount of adaptation are likely to reflect cross-subject differences in the status of the auditory nerve, no predictable relationship was found between these physiologic measures of peripheral neural function and either word recognition or the relationship between ECAP thresholds and MAP levels.
本研究有三个主要目标。第一个目标是评估人工耳蜗使用者的神经适应性变化程度。第二个目标是确定听神经层面的适应性是否与单词识别能力相关。第三个目标是确定外周神经适应性是否对电诱发复合动作电位（ECAP）阈值与言语处理器编程水平之间的关系有影响。
使用神经反应遥测软件记录21名Nucleus人工耳蜗使用者的ECAP。在5分钟内，以三种不同的刺激速率（15、80和300赫兹）进行了一系列110次ECAP记录。用于记录这一系列反应的刺激水平保持恒定，处于或接近受试者确定的300赫兹刺激速率下的最大舒适水平（C级）。从5分钟刺激间隔开始到结束测量的ECAP幅度持续下降被解释为神经适应性的证据。然后使用回归分析程序评估神经适应性与单词识别之间的关系。
在80和300赫兹的刺激速率下，所有21名受试者均观察到显著的适应性水平。使用15赫兹速率时，在5分钟记录期内几乎没有观察到适应性。适应性在300赫兹速率下最大，并且在人工耳蜗使用者之间有很大差异。未发现适应性程度与单词识别之间的关系。适应性程度也未显示会影响低速率记录的ECAP阈值与用于言语处理器编程的水平之间的关系。
人工耳蜗使用者在持续电刺激下经历了不同程度的长期适应性。即使在低至80赫兹的刺激速率下，适应性对ECAP的影响也很明显。尽管适应性程度的变化可能反映了听神经状态的个体差异，但在外周神经功能的这些生理指标与单词识别或ECAP阈值与MAP水平之间的关系中未发现可预测的关系。
