Hashimoto R, Nakano I, MacKinnon C D, Civardi C, Rothwell J C
Department of Neurology, Jichi Medical School.
Rinsho Shinkeigaku. 2001 Feb-Mar;41(2-3):101-6.
It used to be considered that unilateral movements of distal limb parts are associated only with contralateral motor cortical activity. Recent neuroimaging studies, however, suggest that the motor cortex ipsilateral to a task-performing hand is also activated, and that motor patterns in one hand affect the degree of the activity of the ipsilateral motor cortex. If so, muscles of the hand contralateral to a task-performing one may change those excitability depending on types of tasks. We studied eight subjects who performed three different finger tasks by one hand: (a) pinch, (b) sequential finger opposition, and (c) tactile discrimination. Transcranial magnetic stimulation was delivered by a figure eight coil over the hemisphere ipsilateral to a task-performing hand. Motor evoked potentials and background electromyographic activities were recorded from the opponens pollicis muscle contralateral to the stimulated hemisphere. On average, the motor evoked potentials were larger during tactile discrimination task than those at rest in either hand (p < 0.01). Background electromyographic activities in the left hand increased significantly during right hand tactile discrimination task (p < 0.01), whilst those in the right hand did not change during the left hand performance (p > 0.05). These findings suggest the followings: (1) the hand muscle contralateral to a task performing one changes its excitability depending on types of tasks; and (2) increment of excitability of the left hand muscle associated with right hand tactile discrimination is greater than that of the right hand one in association with the same task by the left hand, thus supporting the idea that there is a functional asymmetry between the right and left motor cortex in respect of motor performance.
过去人们认为，肢体远端部分的单侧运动仅与对侧运动皮层活动相关。然而，最近的神经影像学研究表明，执行任务的手同侧的运动皮层也会被激活，并且一只手的运动模式会影响同侧运动皮层的活动程度。如果是这样，执行任务的手对侧的手部肌肉可能会根据任务类型改变其兴奋性。我们研究了8名受试者，他们用一只手执行三种不同的手指任务：(a)捏，(b)顺序手指对掌，以及(c)触觉辨别。通过一个八字形线圈在执行任务的手同侧的半球上进行经颅磁刺激。从受刺激半球对侧的拇对掌肌记录运动诱发电位和背景肌电图活动。平均而言，在触觉辨别任务期间，两只手的运动诱发电位均比静息时更大（p < 0.01）。在右手进行触觉辨别任务期间，左手的背景肌电图活动显著增加（p < 0.01），而在左手执行任务期间，右手的背景肌电图活动没有变化（p > 0.05）。这些发现表明：(1)执行任务的手对侧的手部肌肉会根据任务类型改变其兴奋性；(2)与右手触觉辨别相关的左手肌肉兴奋性增加大于左手执行相同任务时右手肌肉的兴奋性增加，从而支持了在运动表现方面左右运动皮层存在功能不对称的观点。
