Curthoys Ian S
Vestibular Research Laboratory, School of Psychology, University of Sydney, Sydney, New South Wales, Australia,
Audiol Neurootol. 2020;25(1-2):25-34. doi: 10.1159/000502712. Epub 2019 Sep 25.
This paper discusses some of the concepts and major physiological issues in developing a means of electrically stimulating the otolithic system, with the final goal being the electrical stimulation of the otoliths in human patients. It contrasts the challenges of electrical stimulation of the otolith organs as compared to stimulation of the semicircular canals. Electrical stimulation may consist of trains of short-duration pulses (e.g., 0.1 ms duration at 400 Hz) by selective electrodes on otolith maculae or otolithic afferents, or unselective maintained DC stimulation by large surface electrodes on the mastoids - surface galvanic stimulation.
Recent anatomical and physiological results are summarized in order to introduce some of the unique issues in electrical stimulation of the otoliths. The first challenge is that each otolithic macula contains receptors with opposite polarization (opposing preferred directions of stimulation), unlike the uniform polarization of receptors in each semicircular canal crista. The puzzle is that in response to the one linear acceleration in the one macula, some otolithic afferents have an increased activation whereas others have decreased activation. Key Messages: At the vestibular nucleus this opposite receptor hair cell polarization and consequent opposite afferent input allow enhanced response to the one linear acceleration, via a "push-pull" neural mechanism in a manner analogous to the enhancement of semicircular canal responses to angular acceleration. Within each otolithic macula there is not just one uniform otolithic neural input to the brain - there are very distinctly different channels of otolithic neural inputs transferring the neural data to the brainstem. As a simplification these channels are characterized as the sustained and transient systems. Afferents in each system have different responses to stimulus onset and maintained stimulation and likely different projections, and most importantly different thresholds for activation by electrical stimulation and different adaptation rates to maintained stimulation. The implications of these differences are considered.
本文讨论了开发一种电刺激耳石系统方法中的一些概念和主要生理问题，最终目标是对人类患者的耳石进行电刺激。它对比了与刺激半规管相比，电刺激耳石器官所面临的挑战。电刺激可以通过耳石斑或耳石传入神经上的选择性电极施加短持续时间脉冲序列（例如，400赫兹时持续时间为0.1毫秒），或者通过乳突上的大表面电极进行非选择性的持续直流刺激——表面电刺激。
总结了近期的解剖学和生理学结果，以介绍电刺激耳石时的一些独特问题。第一个挑战是，每个耳石斑都包含极化相反（刺激偏好方向相反）的感受器，这与每个半规管嵴中感受器的均匀极化不同。令人困惑的是，在一个耳石斑对一个线性加速度的反应中，一些耳石传入神经的激活增加，而另一些则减少。关键信息：在前庭核，这种相反的感受器毛细胞极化以及随之而来的相反传入输入，通过一种“推挽”神经机制，以类似于半规管对角加速度反应增强的方式，使得对单一线性加速度的反应增强。在每个耳石斑内，并非只有一种统一的耳石神经输入到大脑——存在非常明显不同的耳石神经输入通道，将神经数据传递到脑干。简化来说，这些通道被描述为持续系统和瞬态系统。每个系统中的传入神经对刺激开始和持续刺激有不同的反应，可能有不同的投射，最重要的是，对电刺激的激活阈值不同，对持续刺激的适应率也不同。考虑了这些差异的影响。
