Werner W, Bauswein E, Fromm C
Abteilung Neurobiologie, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Federal Republic of Germany.
Exp Brain Res. 1991;86(2):293-302. doi: 10.1007/BF00228952.
Single cell activity was studied in the postarcuate premotor area (PMA) and primary motor cortex (MI) of two monkeys performing a load-bearing task with the contralateral hand. Steady-state discharge rates were examined in relation to positional maintenance of the wrist which was held in one of three given positions against graded torques directed towards flexion or extension. Significant and monotonic relationships between tonic firing rate and static torque were found in 41% of 477 MI cells and in only 26% of 470 units studied in PMA. However, for specific cell groups in the PMA the proportion of load-related neurons reached that of the MI samples; this was true for pyramidal tract neurons (PTNs) and for 'non-PTNs' if recorded in their vicinity. The most interesting difference pertains to the range of load over which cells in both areas modulated activity. MI neurons showed steepest change of firing rates over a limited range of small torques around zero external load; the population average displayed a sigmoidal relationship. Proportionally more PMA neurons increased their activity over the entire range of torques examined or showed the highest increase with stronger torques; the population average best fitted a quadratic function. The mean firing rate-torque slope of the PMA population was significantly smaller than that of MI. Many cells in either area were related to both torque and joint position and displayed correlates of length-tension properties of muscle. Change of position sensitivity with torque was found to parallel the rate-torque characteristics in individual neurons. Mean position sensitivity of PMA neurons increased with increasing torques in the 'preferred' direction. In contrast, greatest position sensitivity of the MI population occurred over the range of low torques, which means a clear quantitative dissociation from the muscular activities. The results suggest differential roles of MI and PMA in the control of 'fine' versus 'gross' muscular forces. Undoubtedly, some PMA cell elements (possibly certain output neurons) are involved in aspects of postural control of EMG adjustment to load and joint position.
在两只猴子用对侧手执行承重任务时，对其弓状后运动前区（PMA）和初级运动皮层（MI）的单细胞活动进行了研究。针对手腕在三个给定位置之一抵抗指向屈曲或伸展的分级扭矩进行位置维持的情况，检查了稳态放电率。在477个MI细胞中的41%以及在PMA研究的470个单元中的仅26%中，发现了强直放电率与静态扭矩之间存在显著且单调的关系。然而，对于PMA中的特定细胞群，与负荷相关的神经元比例达到了MI样本的比例；对于锥体束神经元（PTN）以及如果在其附近记录的“非PTN”来说确实如此。最有趣的差异在于两个区域的细胞调节活动的负荷范围。MI神经元在零外部负荷附近的有限小扭矩范围内显示出放电率的最急剧变化；总体平均值呈现出S形关系。在整个检查的扭矩范围内，比例上更多的PMA神经元增加了它们的活动，或者在更强的扭矩下显示出最高度的增加；总体平均值最适合二次函数。PMA总体的平均放电率 - 扭矩斜率显著小于MI的。两个区域中的许多细胞都与扭矩和关节位置有关，并显示出肌肉长度 - 张力特性的相关性。发现位置敏感性随扭矩的变化与单个神经元中的速率 - 扭矩特征平行。PMA神经元的平均位置敏感性在“偏好”方向上随着扭矩增加而增加。相比之下，MI总体的最大位置敏感性出现在低扭矩范围内，这意味着与肌肉活动有明显定量解离。结果表明MI和PMA在控制“精细”与“粗略”肌肉力量方面具有不同作用。毫无疑问，一些PMA细胞成分（可能是某些输出神经元）参与了对负荷和关节位置进行肌电图调整的姿势控制方面。
