Center for Hearing Research, Departments of Anatomy and Neurobiology, Biomedical Engineering, Cognitive Sciences, Otolaryngology - Head and Neck Surgery, University of California Irvine, Irvine, CA 92697, United States; Department of Otorhinolaryngology - Head and Neck Surgery, Seoul National University Hospital, Seoul, South Korea.
Center for Hearing Research, Departments of Anatomy and Neurobiology, Biomedical Engineering, Cognitive Sciences, Otolaryngology - Head and Neck Surgery, University of California Irvine, Irvine, CA 92697, United States.
Hear Res. 2022 Mar 1;415:108431. doi: 10.1016/j.heares.2022.108431. Epub 2022 Jan 5.
While noninvasive brain stimulation is convenient and cost effective, its utility is limited by the substantial distance between scalp electrodes and their intended neural targets in the head. The tympanic membrane, or eardrum, is a thin flap of skin deep in an orifice of the head that may serve as a port for improved efficiency of noninvasive stimulation. Here we chose the cochlea as a target because it resides in the densest bone of the skull and is adjacent to many deep-brain-stimulation structures. We also tested the hypothesis that noninvasive electric stimulation of the cochlea may restore neural activities that are missing in acoustic stimulation. We placed an electrode in the ear canal or on the tympanic membrane in 25 human adults (10 females) and compared their stimulation efficiency by characterizing the electrically-evoked auditory sensation. Relative to ear canal stimulation, tympanic membrane stimulation was four times more likely to produce an auditory percept, required eight times lower electric current to reach the threshold and produced two-to-four times more linear suprathreshold responses. We further measured tinnitus suppression in 14 of the 25 subjects who had chronic tinnitus. Compared with ear canal stimulation, tympanic membrane stimulation doubled both the probability (22% vs. 55%) and the amount (-15% vs. -34%) of tinnitus suppression. These findings extended previous work comparing evoked perception and tinnitus suppression between electrodes placed in the ear canal and on the scalp. Together, the previous and present results suggest that the efficiency of conventional scalp-based noninvasive electric stimulation can be improved by at least one order of magnitude via tympanic membrane stimulation. This increased efficiency is most likely due to the shortened distance between the electrode placed on the tympanic membrane and the targeted cochlea. The present findings have implications for the management of tinnitus by offering a potential alternative to interventions using invasive electrical stimulation such as cochlear implantation, or other non-invasive transcranial electrical stimulation methods.
虽然非侵入性脑刺激既方便又具有成本效益，但由于头皮电极与头部目标神经之间存在很大的距离，其效用受到限制。鼓膜是头部孔口深处的一层薄皮肤瓣，可能成为提高非侵入性刺激效率的端口。在这里，我们选择耳蜗作为目标，因为它位于颅骨最密集的骨头中，并且与许多深部脑刺激结构相邻。我们还测试了假设，即耳蜗的非侵入性电刺激可能会恢复在声音刺激中缺失的神经活动。我们在 25 名成年人类（10 名女性）的耳道中或鼓膜上放置了一个电极，并通过描述电诱发的听觉感觉来比较他们的刺激效率。与耳道刺激相比，鼓膜刺激产生听觉感知的可能性高出四倍，达到阈值所需的电流低八倍，产生的超阈值响应线性度高出两到四倍。我们还在 25 名患有慢性耳鸣的受试者中的 14 名中测量了耳鸣抑制。与耳道刺激相比，鼓膜刺激使耳鸣抑制的概率（22%对 55%）和幅度（-15%对-34%）均增加了一倍。这些发现扩展了先前比较放置在耳道和头皮上的电极之间诱发感知和耳鸣抑制的工作。总的来说，以前和现在的结果表明，通过鼓膜刺激，至少可以将常规基于头皮的非侵入性电刺激的效率提高一个数量级。这种效率的提高很可能是由于放置在鼓膜上的电极与目标耳蜗之间的距离缩短。目前的研究结果对耳鸣的管理具有重要意义，为提供了一种替代方案，避免了使用侵入性电刺激（如耳蜗植入）或其他非侵入性经颅电刺激方法的干预。
