Kim Juno, Curthoys Ian S
The Vestibular Research Laboratory, School of Psychology, The University of Sydney, NSW 2006, Australia.
Brain Res Bull. 2004 Sep 30;64(3):265-71. doi: 10.1016/j.brainresbull.2004.07.008.
Previous studies in humans and animals which have shown that DC galvanic vestibular stimulation (GVS) induces horizontal and torsional eye movements have been interpreted as being due to a preferential activation of primary vestibular afferents innervating the horizontal semicircular canals and otoliths by GVS. The present study sought to determine in guinea pigs whether GVS does indeed selectively activate primary horizontal canal and otolith afferents. Constant-current GVS was passed between electrodes implanted in the tensor-tympani muscle of each middle ear or between electrodes on the skin over the mastoid. During this stimulation, responses from single primary vestibular neurons were recorded extracellularly by glass microelectrodes in Scarpa's ganglion. Afferents from all vestibular sensory regions were activated by both surface and tensor-tympani galvanic stimulation. Tensor tympani GVS was approximately 10 times more effective than surface GVS. At larger current intensities irregularly discharging afferents showed an asymmetrical response: cathodal stimulation resulted in a larger change in firing (increase) than anodal stimulation (decrease), whereas regularly discharging afferents responded symmetrically to the two polarities of GVS. Across all afferents tuned for different types of natural vestibular stimulation, neuronal sensitivity for GVS was found to increase with discharge variability (as indexed by CV*). Anterior canal afferents showed a slightly higher sensitivity than afferents from other vestibular sensory regions. Hence, the present study concluded that GVS activates primary vestibular afferents innervating all sensory regions in a uniform fashion. Therefore, the specific pattern of GVS-induced eye movements reported in previous studies are not due to differential sensitivity between different vestibular sensory regions, but are likely to reflect an involvement of central processing.
先前在人类和动物身上进行的研究表明，直流电前庭刺激（GVS）会诱发水平和扭转性眼球运动，这些研究被解释为是由于GVS优先激活了支配水平半规管和耳石的初级前庭传入神经。本研究旨在确定在豚鼠中，GVS是否确实选择性地激活初级水平半规管和耳石传入神经。恒定电流GVS通过植入每只中耳镫骨肌的电极之间或乳突上方皮肤电极之间传递。在这种刺激过程中，通过Scarpa神经节中的玻璃微电极细胞外记录单个初级前庭神经元的反应。表面和镫骨肌直流电刺激均激活了来自所有前庭感觉区域的传入神经。镫骨肌GVS的效果比表面GVS大约高10倍。在较大电流强度下，不规则放电的传入神经表现出不对称反应：阴极刺激导致放电变化（增加）比阳极刺激（减少）更大，而规则放电的传入神经对GVS的两种极性反应对称。在所有针对不同类型自然前庭刺激进行调谐的传入神经中，发现神经元对GVS的敏感性随着放电变异性（以CV*为指标）增加。前半规管传入神经的敏感性略高于其他前庭感觉区域的传入神经。因此，本研究得出结论，GVS以统一方式激活支配所有感觉区域的初级前庭传入神经。所以，先前研究中报道的GVS诱发的眼球运动的特定模式并非由于不同前庭感觉区域之间的敏感性差异，而可能反映了中枢处理的参与。
