Department of Biomedical Engineering, University of Minnesota, Twin Cities, Minneapolis, Minnesota, USA.
J Neurophysiol. 2013 Aug;110(4):1009-20. doi: 10.1152/jn.00022.2013. Epub 2013 May 29.
While the cochlear implant has successfully restored hearing to many deaf patients, it cannot benefit those without a functional auditory nerve or an implantable cochlea. As an alternative, the auditory midbrain implant (AMI) has been developed and implanted into deaf patients. Consisting of a single-shank array, the AMI is designed for stimulation along the tonotopic gradient of the inferior colliculus (ICC). Although the AMI can provide frequency cues, it appears to insufficiently transmit temporal cues for speech understanding because repeated stimulation of a single site causes strong suppressive and refractory effects. Applying the electrical stimulation to at least two sites within an isofrequency lamina can circumvent these refractory processes. Moreover, coactivation with short intersite delays (<5 ms) can elicit cortical activation which is enhanced beyond the summation of activity induced by the individual sites. The goal of our study was to further investigate the role of the auditory cortex in this enhancement effect. In guinea pigs, we electrically stimulated two locations within an ICC lamina or along different laminae with varying interpulse intervals (0-10 ms) and recorded activity in different locations and layers of primary auditory cortex (A1). Our findings reveal a neural mechanism that integrates activity only from neurons located within the same ICC lamina for short spiking intervals (<6 ms). This mechanism leads to enhanced activity into layers III-V of A1 that is further magnified in supragranular layers. This integration mechanism may contribute to perceptual coding of different sound features that are relevant for improving AMI performance.
虽然人工耳蜗已经成功地为许多失聪患者恢复了听力，但它对没有功能听觉神经或可植入耳蜗的患者没有帮助。作为替代方案，听觉中脑植入物（AMI）已经开发并植入到失聪患者中。AMI 由单根阵列组成，旨在沿着下丘的音调梯度进行刺激。尽管 AMI 可以提供频率线索，但它似乎不足以传递语音理解所需的时间线索，因为单个部位的重复刺激会引起强烈的抑制和不应期效应。在同频层内的至少两个部位施加电刺激可以避免这些不应期过程。此外，短的部位间延迟（<5ms）的共激活可以引发皮层激活，其增强超过单个部位引起的活动的总和。我们的研究目的是进一步研究听觉皮层在这种增强效应中的作用。在豚鼠中，我们用电刺激 ICC 层内的两个位置或沿着不同的层以不同的脉冲间间隔（0-10ms）刺激，并记录初级听觉皮层（A1）的不同位置和层中的活动。我们的发现揭示了一种神经机制，该机制仅整合来自同一 ICC 层内神经元的活动，用于短的脉冲间隔（<6ms）。这种机制导致 A1 的第三到第五层的活动增强，在颗粒层以上进一步放大。这种整合机制可能有助于不同声音特征的感知编码，这对于改善 AMI 的性能很重要。
