Bonsu Angela N, Nousi Sofia, Lobo Rhannon, Strutton Paul H, Arshad Qadeer, Bronstein Adolfo M
Neuro-Otology Unit, Department of Brain Sciences, Charing Cross Hospital Campus, Imperial College London, Fulham Palace Road, London, W6 8RF, UK.
Division of Surgery, Anaesthetics, and Intensive Care, Department of Musculoskeletal Surgery, Faculty of Medicine, Imperial College London, Charing Cross Hospital Campus, London, W6 8RF, UK.
Exp Brain Res. 2021 Jul;239(7):2141-2149. doi: 10.1007/s00221-021-06123-7. Epub 2021 May 9.
The vestibular system facilitates gaze and postural stability via the vestibulo-ocular (VOR) and vestibulo-spinal reflexes, respectively. Cortical and perceptual mechanisms can modulate long-duration VOR responses, but little is known about whether high-order neural phenomena can modulate short-latency vestibulo-spinal responses. Here, we investigate this by assessing click-evoked cervical vestibular myogenic-evoked potentials (VEMPS) during visual roll motion that elicited an illusionary sensation of self-motion (i.e. vection). We observed that during vection, the amplitude of the VEMPs was enhanced when compared to baseline measures. This modulation in VEMP amplitude was positively correlated with the subjective reports of vection strength. That is, those subjects reporting greater subjective vection scores exhibited a greater increase in VEMP amplitude. Control experiments showed that simple arousal (cold-induced discomfort) also increased VEMP amplitude but that, unlike vection, it did not modulate VEMP amplitude linearly. In agreement, small-field visual roll motion that did not induce vection failed to increase VEMP amplitude. Taken together, our results demonstrate that vection can modify the response of vestibulo-collic reflexes. Even short-latency brainstem vestibulo-spinal reflexes are influenced by high-order mechanisms, illustrating the functional importance of perceptual mechanisms in human postural control. As VEMPs are inhibitory responses, we argue that the findings may represent a mechanism whereby high-order CNS mechanisms reduce activity levels in vestibulo-collic reflexes, necessary for instance when voluntary head movements need to be performed.
前庭系统分别通过前庭眼反射（VOR）和前庭脊髓反射促进眼球凝视和姿势稳定性。皮层和感知机制可以调节长时间的VOR反应，但对于高阶神经现象是否能调节短潜伏期的前庭脊髓反应却知之甚少。在此，我们通过评估在视觉侧滚运动期间诱发自我运动错觉（即运动错觉）的点击诱发的颈前庭肌源性诱发电位（VEMPs）来对此进行研究。我们观察到，在运动错觉期间，与基线测量相比，VEMPs的幅度增强。VEMP幅度的这种调节与运动错觉强度的主观报告呈正相关。也就是说，那些报告主观运动错觉得分较高的受试者，其VEMP幅度增加得更大。对照实验表明，单纯的唤醒（冷诱导不适）也会增加VEMP幅度，但与运动错觉不同的是，它不会线性调节VEMP幅度。同样，未诱发运动错觉的小视野视觉侧滚运动未能增加VEMP幅度。综上所述，我们的结果表明，运动错觉可以改变前庭颈反射的反应。即使是短潜伏期的脑干前庭脊髓反射也受高阶机制的影响，这说明了感知机制在人体姿势控制中的功能重要性。由于VEMPs是抑制性反应，我们认为这些发现可能代表了一种机制，即高阶中枢神经系统机制降低前庭颈反射中的活动水平，例如在需要进行自主头部运动时这是必要的。
