Department of Biomedical Engineering, Johns Hopkins School of Medicine , Baltimore, Maryland.
Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins School of Medicine , Baltimore, Maryland.
J Neurophysiol. 2019 Jun 1;121(6):2256-2266. doi: 10.1152/jn.00887.2018. Epub 2019 Apr 17.
Electrical stimulation of vestibular afferent neurons to partially restore semicircular canal sensation of head rotation and the stabilizing reflexes that sensation supports has potential to effectively treat individuals disabled by bilateral vestibular hypofunction. Ideally, a vestibular implant system using this approach would be integrated with a cochlear implant, which would provide clinicians with a means to simultaneously treat loss of both vestibular and auditory sensation. Despite obvious similarities, merging these technologies poses several challenges, including stimulus pulse timing errors that arise when a system must implement a pulse frequency modulation-encoding scheme (as is used in vestibular implants to mimic normal vestibular nerve encoding of head movement) within fixed-rate continuous interleaved sampling (CIS) strategies used in cochlear implants. Pulse timing errors caused by temporal discretization inherent to CIS create stair step discontinuities of the vestibular implant's smooth mapping of head velocity to stimulus pulse frequency. In this study, we assayed electrically evoked vestibuloocular reflex responses in two rhesus macaques using both a smooth pulse frequency modulation map and a discretized map corrupted by temporal errors typical of those arising in a combined cochlear-vestibular implant. Responses were measured using three-dimensional scleral coil oculography for prosthetic electrical stimuli representing sinusoidal head velocity waveforms that varied over 50-400°/s and 0.1-5 Hz. Pulse timing errors produced negligible effects on responses across all canals in both animals, indicating that temporal discretization inherent to implementing a pulse frequency modulation-coding scheme within a cochlear implant's CIS fixed pulse timing framework need not sacrifice performance of the combined system's vestibular implant portion. Merging a vestibular implant system with existing cochlear implant technology can provide clinicians with a means to restore both vestibular and auditory sensation. Pulse timing errors inherent to integration of pulse frequency modulation vestibular stimulation with fixed-rate, continuous interleaved sampling cochlear implant stimulation would discretize the smooth head velocity encoding of a combined device. In this study, we show these pulse timing errors produce negligible effects on electrically evoked vestibulo-ocular reflex responses in two rhesus macaques.
前庭传入神经元的电刺激部分恢复了半规管对头部旋转的感觉和感觉支持的稳定反射，有可能有效地治疗双侧前庭功能低下导致的残疾个体。理想情况下，使用这种方法的前庭植入系统将与人工耳蜗植入系统相结合，这将为临床医生提供一种同时治疗前庭和听觉感觉丧失的方法。尽管有明显的相似之处，但将这些技术融合在一起存在一些挑战，包括当系统必须在固定速率连续交错采样（CIS）策略（如在人工耳蜗植入物中用于模拟正常前庭神经对头部运动的编码）中实现脉冲频率调制编码方案（如前庭植入物中用于模拟正常前庭神经对头部运动的编码）时，会出现刺激脉冲定时误差。CIS 固有的时间离散化引起的脉冲定时误差导致前庭植入物将头部速度平稳映射到刺激脉冲频率的过程中出现阶梯式不连续性。在这项研究中，我们使用两种恒河猴评估了电诱发的前庭眼反射反应，使用平滑脉冲频率调制图和受时间误差影响的离散化图，这些误差是在组合的耳蜗-前庭植入物中产生的。使用三维巩膜线圈眼动图测量了代表头部速度正弦波的假体电刺激的反应，这些正弦波的变化范围为 50-400°/s 和 0.1-5 Hz。在两个动物的所有管道中，脉冲定时误差对响应的影响可以忽略不计，这表明在耳蜗植入物的 CIS 固定脉冲定时框架内实现脉冲频率调制编码方案固有的时间离散化不需要牺牲组合系统的前庭植入部分的性能。将前庭植入系统与现有的人工耳蜗技术相结合，可以为临床医生提供一种恢复前庭和听觉感觉的方法。将脉冲频率调制前庭刺激与固定速率连续交错采样耳蜗植入刺激相结合所固有的脉冲定时误差会离散组合设备的平滑头部速度编码。在这项研究中，我们表明这些脉冲定时误差对两只恒河猴的电诱发前庭眼反射反应几乎没有影响。
