Rosenkranz Karin, Rothwell John C
Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, 8-11 Queen Square, London, WC1N 3BG, UK.
Eur J Neurosci. 2006 Feb;23(3):822-9. doi: 10.1111/j.1460-9568.2006.04605.x.
Several experimental protocols induce lasting changes in the excitability of motor cortex. Some involve direct cortical stimulation, others activate the somatosensory system and some combine motor and sensory stimulation. The effects usually are measured as changes in amplitude of the motor-evoked-potential (MEP) or short-interval intracortical inhibition (SICI) elicited by a single or paired pulses of transcranial magnetic stimulation (TMS). Recent work has also tested sensorimotor organization within the motor cortex by recording MEPs and SICI during short periods of vibration applied to single intrinsic hand muscles. Here sensorimotor organization is focal: MEPs increase and SICI decreases in the vibrated muscle, whilst the opposite occurs in neighbouring muscles. In six volunteers we compared the after effects of three protocols that lead to lasting changes in cortical excitability: (i) paired associative stimulation (PAS) between a TMS pulse and an electrical stimulus to the median nerve; (ii) motor practice of rapid thumb abduction; and (iii) sensory input produced by semicontinuous muscle vibration, on MEPs and SICI at rest and on the sensorimotor organization. PAS increased MEP amplitudes, whereas vibration changed sensorimotor organization. Motor practice had a dual effect and increased MEPs as well as affecting sensorimotor organization. The implication is that different protocols target different sets of cortical circuits. We speculate that protocols that involve repeated activation of motor cortical output lead to lasting changes in efficacy of synaptic connections in output circuits, whereas protocols that emphasize sensory inputs affect the strength of sensory inputs to motor circuits.
几种实验方案可引起运动皮层兴奋性的持久变化。一些方案涉及直接皮层刺激，另一些则激活体感系统，还有一些将运动和感觉刺激结合起来。这些效应通常通过经颅磁刺激（TMS）单脉冲或双脉冲诱发的运动诱发电位（MEP）或短间隔皮层内抑制（SICI）的幅度变化来测量。最近的研究还通过在对单个手部固有肌施加短时间振动期间记录MEP和SICI，测试了运动皮层内的感觉运动组织。在这里，感觉运动组织是局部性的：在受振动的肌肉中，MEP增加而SICI减少，而在相邻肌肉中则相反。我们在六名志愿者中比较了三种导致皮层兴奋性持久变化的方案的后续效应：（i）TMS脉冲与正中神经电刺激之间的配对联合刺激（PAS）；（ii）快速拇指外展的运动练习；（iii）半连续肌肉振动产生的感觉输入，对静息时的MEP和SICI以及感觉运动组织的影响。PAS增加了MEP幅度，而振动改变了感觉运动组织。运动练习具有双重作用，增加了MEP并影响了感觉运动组织。这意味着不同的方案针对不同的皮层回路。我们推测，涉及运动皮层输出反复激活的方案会导致输出回路中突触连接效能的持久变化，而强调感觉输入的方案会影响运动回路中感觉输入的强度。
