National Military Audiology and Speech Pathology Center, Walter Reed National Military Medical Center, Bethesda, Maryland 20889
National Military Audiology and Speech Pathology Center, Walter Reed National Military Medical Center, Bethesda, Maryland 20889.
J Neurosci. 2021 Dec 8;41(49):10161-10178. doi: 10.1523/JNEUROSCI.0359-21.2021. Epub 2021 Nov 1.
Bilateral cochlear implants (BI-CIs) or a CI for single-sided deafness (SSD-CI; one normally functioning acoustic ear) can partially restore spatial-hearing abilities, including sound localization and speech understanding in noise. For these populations, however, interaural place-of-stimulation mismatch can occur and thus diminish binaural sensitivity that relies on interaurally frequency-matched neurons. This study examined whether plasticity-reorganization of central neural pathways over time-can compensate for peripheral interaural place mismatch. We hypothesized differential plasticity across two systems: none for binaural processing but adaptation for pitch perception toward frequencies delivered by the specific electrodes. Interaural place mismatch was evaluated in 19 BI-CI and 23 SSD-CI human subjects (both sexes) using binaural processing (interaural-time-difference discrimination with simultaneous bilateral stimulation), pitch perception (pitch ranking for single electrodes or acoustic tones with sequential bilateral stimulation), and physical electrode-location estimates from computed-tomography (CT) scans. On average, CT scans revealed relatively little BI-CI interaural place mismatch (26° insertion-angle mismatch) but a relatively large SSD-CI mismatch, particularly at low frequencies (166° for an electrode tuned to 300 Hz, decreasing to 14° at 7000 Hz). For BI-CI subjects, the three metrics were in agreement because there was little mismatch. For SSD-CI subjects, binaural and CT measurements were in agreement, suggesting little binaural-system plasticity induced by mismatch. The pitch measurements disagreed with binaural and CT measurements, suggesting place-pitch plasticity or a procedural bias. These results suggest that reducing interaural place mismatch and potentially improving binaural processing by reprogramming the CI frequency allocation would be better done using CT-scan than pitch information. Electrode-array placement for cochlear implants (bionic prostheses that partially restore hearing) does not explicitly align neural representations of frequency information. The resulting interaural place-of-stimulation mismatch can diminish spatial-hearing abilities. In this study, adults with two cochlear implants showed reasonable interaural alignment, whereas those with one cochlear implant but normal hearing in the other ear often showed mismatch. In cases of mismatch, binaural sensitivity was best when the same cochlear locations were stimulated in both ears, suggesting that binaural brainstem pathways do not experience plasticity to compensate for mismatch. In contrast, interaurally pitch-matched electrodes deviated from cochlear-location estimates and did not optimize binaural sensitivity. Clinical correction of interaural place mismatch using binaural or computed-tomography (but not pitch) information may improve spatial-hearing benefits.
双侧人工耳蜗植入（BI-CI）或单侧聋（SSD-CI；一只正常工作的听觉耳）人工耳蜗植入可以部分恢复空间听觉能力，包括声音定位和噪声中的言语理解。然而，对于这些人群，刺激的耳间位置不匹配可能会发生，从而降低依赖于耳间频率匹配神经元的双耳敏感性。本研究旨在探讨中枢神经通路的可塑性和重组是否能随着时间的推移补偿外周耳间位置不匹配。我们假设两种系统的可塑性不同：双耳处理无变化，但对特定电极刺激频率的音调感知具有适应性。使用双耳处理（双耳时间差辨别，双侧同时刺激）、音调感知（单个电极或双侧顺序刺激时的音调排序）和计算机断层扫描（CT）扫描的物理电极位置估计，对 19 名 BI-CI 和 23 名 SSD-CI 人类受试者（男女）进行了耳间位置不匹配评估。平均而言，CT 扫描显示 BI-CI 耳间位置不匹配相对较小（26°插入角不匹配），但 SSD-CI 不匹配较大，特别是在低频时（调谐至 300Hz 的电极为 166°，7000Hz 时降至 14°）。对于 BI-CI 受试者，三个指标是一致的，因为不匹配很小。对于 SSD-CI 受试者，双耳和 CT 测量结果一致，表明不匹配引起的双耳系统可塑性较小。音调测量结果与双耳和 CT 测量结果不一致，表明音调可塑性或程序偏差。这些结果表明，通过重新编程 CI 频率分配来减少耳间位置不匹配并可能改善双耳处理，使用 CT 扫描比音调信息更好。人工耳蜗（部分恢复听力的仿生假体）的电极阵列放置没有明确对齐频率信息的神经表示。由此产生的耳间刺激位置不匹配会降低空间听觉能力。在这项研究中，双耳植入的成年人表现出合理的耳间对齐，而那些单耳植入但另一只耳朵听力正常的成年人通常表现出不匹配。在不匹配的情况下，当双耳刺激相同的耳蜗位置时，双耳敏感性最佳，这表明双耳脑干通路不会经历可塑性以补偿不匹配。相比之下，耳间音调匹配的电极偏离耳蜗位置估计，并且不能优化双耳敏感性。使用双耳或计算机断层扫描（但不是音调）信息校正耳间位置不匹配可能会改善空间听觉益处。
