Weinberg H, Cheyne D, Crisp D
Department of Psychology, Simon Fraser University, Burnaby, British Columbia, Canada.
Adv Neurol. 1990;54:193-205.
Although a great deal has been learned from the study of scalp-recorded movement-related potentials, the exact origin of the various components described above remains unclear, mainly because of the limited spatial resolution of the EEG and the consequent difficulty in predicting sources from the surface distribution of these components. The introduction of the MEG and source localization methods based on neuromagnetic recordings has provided a new means by which to study the cortical activation during movement in humans. The study of movement-related magnetic fields of the brain is still at an early stage of development. However, the data reviewed to date indicate that the MEG offers a promising means by which to study (noninvasively) cortical motor function. With regard to the data reviewed here, the following conclusions can be made: 1. Slow "readiness" magnetic fields can be recorded prior to a variety of voluntary movements and display a topography which indicates the activation of bilateral sources, even if the instructed movement is unilateral. Sources in the contralateral hemisphere appear as early as 0.5 sec before the movement and appear to be localized in the sensorimotor cortex. Consequently, the assumption of a contralateral source being the only or primary generator of the readiness potential, based on EEG data, must be tempered. 2. A large-amplitude "movement-evoked field" (occurring at a post-EMG-onset latency of about 110 msec for finger movements) is probably the counterpart of the MP and appears to be the result of a dipolar source localized to the contralateral sensorimotor area. This source is probably the first sign of movement reafferent input to cortex. 3. Variability in the movement-evoked field across individuals, which are much more evident in MEG than in EEG, may reflect the summation of multiple sources active in the region of the sensorimotor cortex during movement onset (i.e., both pre- and postcentral generators). In some instances, it may be possible to extract simpler elements of these complex sources based on assumptions of temporal overlapping of pre-movement and movement-evoked activity.
尽管通过对头皮记录的运动相关电位的研究已经获得了大量知识，但上述各种成分的确切起源仍不清楚，主要是因为脑电图（EEG）的空间分辨率有限，以及由此导致的根据这些成分的表面分布预测其来源的困难。脑磁图（MEG）和基于神经磁记录的源定位方法的引入，为研究人类运动过程中的皮层激活提供了一种新手段。对大脑运动相关磁场的研究仍处于早期发展阶段。然而，迄今为止所回顾的数据表明，MEG为（非侵入性地）研究皮层运动功能提供了一种有前景的手段。关于这里所回顾的数据，可以得出以下结论：1. 在各种自主运动之前，可以记录到缓慢的“准备”磁场，其地形图显示双侧源的激活，即使指令运动是单侧的。对侧半球的源在运动前0.5秒就出现，似乎定位于感觉运动皮层。因此，基于EEG数据认为对侧源是准备电位的唯一或主要发生器的假设必须加以修正。2. 一个大振幅的“运动诱发场”（手指运动时在肌电图开始后约110毫秒的潜伏期出现）可能与运动电位（MP）相对应，似乎是定位于对侧感觉运动区的偶极源的结果。这个源可能是运动再传入输入到皮层的第一个迹象。3. 个体间运动诱发场的变异性在MEG中比在EEG中更明显，这可能反映了运动开始时感觉运动皮层区域中多个活跃源的总和（即中央前回和中央后回的发生器）。在某些情况下，根据运动前和运动诱发活动的时间重叠假设，有可能提取这些复杂源的更简单成分。
