Iwata Nobue K, Ugawa Yoshikazu
Department of Neurology, Division of Neuroscience, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan.
Cerebellum. 2005;4(4):218-23. doi: 10.1080/14734220500277007.
The cerebellum regulates execution of skilled movements through neural connections with the primary motor cortex. A main projection from the cerebellum to the primary motor cortex is a disynaptic excitatory pathway relayed at the ventral thalamus. This dentatothalamocortical pathway receives inhibitory inputs from Purkinje cells of the cerebellar cortex. These pathways (cerebellothalamocortical pathways) have been characterized extensively using cellular approaches in animals. Advances in non-invasive transcranial activation of neural structures using electrical and magnetic stimulation have allowed us to investigate these neural connections in humans. This review summarizes various studies of the cerebellothalamocortical pathway in humans using current transcranial electrical and magnetic stimulation techniques. We studied effects on motor cortical excitability elicited by electrical or magnetic stimulation over the cerebellum by recording surface electromyographic (EMG) responses from the first dorsal interosseous (FDI) muscle. Magnetic stimuli were given with a round or figure eight coil (test stimulation) for primary motor cortical activation. For cerebellar stimulation, we gave high-voltage electrical stimuli or magnetic stimuli through a cone-shaped coil ipsilateral to the surface EMG recording (conditioning stimulation). We examined effects of interstimulus intervals (ISIs) with randomized condition-test paradigm, using a test stimulus given preceded by a conditioning stimulus by ISIs of several milliseconds. We demonstrated significant gain of EMG responses at an ISI of 3 ms (facilitatory effect) and reduced responses starting at 5 ms, which lasted 3-7 ms (inhibitory effect). We applied this method to patients with ataxia and showed that the inhibitory effect was only absent in patients with a lesion at cerebellar efferent pathways or dentatothalamocortical pathway. These results imply that this method activates the unilateral cerebellar structures. We confirmed facilitatory and inhibitory natures of cerebellothalamocortical pathways in humans. We can differentiate ataxia attributable to somewhere in the cerebello-thalamo-cortical pathways from that caused by other pathways.
小脑通过与初级运动皮层的神经连接来调节熟练运动的执行。从小脑到初级运动皮层的主要投射是一条在腹侧丘脑中继的双突触兴奋性通路。这条齿状核 - 丘脑 - 皮质通路接收来自小脑皮质浦肯野细胞的抑制性输入。这些通路（小脑 - 丘脑 - 皮质通路）已在动物中通过细胞方法进行了广泛表征。使用电刺激和磁刺激对神经结构进行非侵入性经颅激活的进展使我们能够在人类中研究这些神经连接。本综述总结了使用当前经颅电刺激和磁刺激技术对人类小脑 - 丘脑 - 皮质通路的各种研究。我们通过记录第一背侧骨间肌（FDI）的表面肌电图（EMG）反应，研究了对小脑进行电刺激或磁刺激所引起的运动皮层兴奋性的影响。使用圆形或八字形线圈进行磁刺激（测试刺激）以激活初级运动皮层。对于小脑刺激，我们通过与表面EMG记录同侧的锥形线圈给予高压电刺激或磁刺激（条件刺激）。我们使用随机条件 - 测试范式检查了刺激间隔（ISI）的影响，使用在条件刺激之后以几毫秒的ISI给予测试刺激。我们证明在ISI为3毫秒时EMG反应有显著增强（促进作用），而从5毫秒开始反应减弱，持续3 - 7毫秒（抑制作用）。我们将此方法应用于共济失调患者，结果表明只有小脑传出通路或齿状核 - 丘脑 - 皮质通路有病变的患者不存在抑制作用。这些结果表明该方法可激活单侧小脑结构。我们证实了人类小脑 - 丘脑 - 皮质通路的促进和抑制性质。我们可以将小脑 - 丘脑 - 皮质通路某处病变引起的共济失调与其他通路引起的共济失调区分开来。
