Croner Albert M, Heshmat Amirreza, Schrott-Fischer Anneliese, Glueckert Rudolf, Hemmert Werner, Bai Siwei
Department of Electrical and Computer Engineering, Technical University of Munich, Munich, Germany.
Munich Institute of Biomedical Engineering, Technical University of Munich, Garching, Germany.
Front Neurosci. 2022 Jul 6;16:914876. doi: 10.3389/fnins.2022.914876. eCollection 2022.
After hearing loss retrograde degeneration of spiral ganglion neurons (SGNs) has been described. Studies modeling the effects of degeneration mostly omitted peripheral processes (dendrites). Recent experimental observations indicated that degenerating SGNs manifested also a reduced diameter of their dendrites. We simulated populations of 400 SGNs inside a high resolution cochlear model with a cochlear implant, based on μCT scans of a human temporal bone. Cochlear implant stimuli were delivered as biphasic pulses in a monopolar configuration. Three SGN situations were simulated, based on our previous measurements of human SGN dendrites: (A) SGNs with intact dendrites (before degeneration), (B) degenerating SGNs, dendrites with a smaller diameter but original length, (C) degenerating SGNs, dendrites omitted. SGN fibers were mapped to characteristic frequency, and place pitch was estimated from excitation profiles. Results from degenerating SGNs (B, C) were similar. Most action potentials were initiated in the somatic area for all cases (A, B, C), except for areas near stimulating electrodes in the apex with intact SGNs (A), where action potentials were initiated in the distal dendrite. In most cases, degenerating SGNs had lower thresholds than intact SGNs (A) (down to -2 dB). Excitation profiles showed increased ectopic activation, i.e., activation of unintended neuronal regions, as well as similar neuronal regions excited by different apical electrodes, for degenerating SGNs (B, C). The estimated pitch showed cases of pitch reversals in apical electrodes for intact SGNs (A), as well as mostly identical pitches evoked by the four most apical electrodes for degenerating SGNs (B, C). In conclusion, neuronal excitation profiles to electrical stimulation exhibited similar traits in both ways of modeling SGN degeneration. Models showed degeneration of dendrites caused increased ectopic activation, as well as similar excitation profiles and pitch evoked by different apical electrodes. Therefore, insertion of electrodes beyond approximately 450° may not provide any benefit if SGN dendrites are degenerated.
听力损失后，螺旋神经节神经元（SGNs）的逆行性变性已有描述。模拟变性影响的研究大多忽略了外周突起（树突）。最近的实验观察表明，变性的SGNs其树突直径也减小。我们基于人类颞骨的μCT扫描，在带有人工耳蜗的高分辨率耳蜗模型中模拟了400个SGN的群体。人工耳蜗刺激以单极配置的双相脉冲形式传递。基于我们之前对人类SGN树突的测量，模拟了三种SGN情况：（A）树突完整的SGNs（变性前），（B）变性的SGNs，树突直径较小但长度不变，（C）变性的SGNs，省略树突。将SGN纤维映射到特征频率，并根据兴奋分布图估计位置音调。变性SGNs（B、C）的结果相似。在所有情况（A、B、C）中，大多数动作电位在胞体区域起始，但在树突完整的SGNs（A）的顶端靠近刺激电极的区域除外，在该区域动作电位在远端树突起始。在大多数情况下，变性的SGNs阈值低于完整的SGNs（A）（低至-2 dB）。对于变性的SGNs（B、C），兴奋分布图显示异位激活增加，即意外神经元区域的激活，以及不同顶端电极激发的相似神经元区域。估计的音调显示，对于完整的SGNs（A），顶端电极存在音调反转情况，而对于变性的SGNs（B、C），四个最顶端电极诱发的音调大多相同。总之，对电刺激的神经元兴奋分布图在模拟SGN变性的两种方式中表现出相似特征。模型显示树突变性导致异位激活增加，以及不同顶端电极诱发的相似兴奋分布图和音调。因此，如果SGN树突发生变性，电极插入超过约450°可能不会带来任何益处。
