Department of Otorhinolaryngology, Hannover Medical University Hannover, Germany.
Front Neural Circuits. 2013 Oct 21;7:166. doi: 10.3389/fncir.2013.00166. eCollection 2013.
The auditory midbrain implant (AMI) consists of a single shank array (20 sites) for stimulation along the tonotopic axis of the central nucleus of the inferior colliculus (ICC) and has been safely implanted in deaf patients who cannot benefit from a cochlear implant (CI). The AMI improves lip-reading abilities and environmental awareness in the implanted patients. However, the AMI cannot achieve the high levels of speech perception possible with the CI. It appears the AMI can transmit sufficient spectral cues but with limited temporal cues required for speech understanding. Currently, the AMI uses a CI-based strategy, which was originally designed to stimulate each frequency region along the cochlea with amplitude-modulated pulse trains matching the envelope of the bandpass-filtered sound components. However, it is unclear if this type of stimulation with only a single site within each frequency lamina of the ICC can elicit sufficient temporal cues for speech perception. At least speech understanding in quiet is still possible with envelope cues as low as 50 Hz. Therefore, we investigated how ICC neurons follow the bandpass-filtered envelope structure of natural stimuli in ketamine-anesthetized guinea pigs. We identified a subset of ICC neurons that could closely follow the envelope structure (up to ~100 Hz) of a diverse set of species-specific calls, which was revealed by using a peripheral ear model to estimate the true bandpass-filtered envelopes observed by the brain. Although previous studies have suggested a complex neural transformation from the auditory nerve to the ICC, our data suggest that the brain maintains a robust temporal code in a subset of ICC neurons matching the envelope structure of natural stimuli. Clinically, these findings suggest that a CI-based strategy may still be effective for the AMI if the appropriate neurons are entrained to the envelope of the acoustic stimulus and can transmit sufficient temporal cues to higher centers.
听觉中脑植入物（AMI）由一个用于刺激沿下丘中央核（ICC）的音调轴的单针阵列（20 个位点）组成，已安全植入不能从耳蜗植入物（CI）中受益的聋人患者中。AMI 提高了植入患者的唇读能力和环境意识。然而，AMI 无法达到 CI 可能实现的高水平语音感知。似乎 AMI 可以传输足够的频谱线索，但对于语音理解所需的时间线索有限。目前，AMI 使用基于 CI 的策略，该策略最初旨在使用与带通滤波声音分量的包络匹配的幅度调制脉冲串刺激沿着耳蜗的每个频率区域。然而，尚不清楚在 ICC 的每个频率层内仅用一个位点进行这种刺激是否可以产生足够的时间线索来实现语音感知。至少在安静环境中，使用低于 50 Hz 的包络线索仍然可以进行语音理解。因此，我们研究了在氯胺酮麻醉的豚鼠中，ICC 神经元如何跟随自然刺激的带通滤波包络结构。我们确定了一组 ICC 神经元，它们可以紧密跟随（高达约 100 Hz）一组物种特异性叫声的包络结构，这是通过使用外围耳朵模型来估计大脑观察到的真实带通滤波包络来揭示的。尽管先前的研究表明从听神经到 ICC 的神经转换复杂，但我们的数据表明，大脑在一组 ICC 神经元中保持了强大的时间编码，与自然刺激的包络结构匹配。临床上，如果适当的神经元被声刺激的包络激发并且能够传递足够的时间线索到更高的中枢，基于 CI 的策略可能仍然对 AMI 有效。
