Maier M A, Perlmutter S I, Fetz E E
Department of Physiology and Biophysics and Regional Primate Research Center, University of Washington, Seattle, Washington 98195, USA.
J Neurophysiol. 1998 Nov;80(5):2495-513. doi: 10.1152/jn.1998.80.5.2495.
The activity of C6-T1 spinal cord neurons was recorded in three macaques while they generated isometric wrist flexion and extension torques in visually guided step-tracking tasks. Electromyographic activity (EMG) was recorded in </=12 independent forearm muscles. Spike-triggered averages (STAs) of rectified and unrectified EMG were used to classify neurons into four groups. Motoneurons (MNs) had a clear postspike motor unit signature in the unrectified STA of one muscle. Premotor interneurons (PreM-INs) had postspike effects in at least one muscle, with onset latencies of >/=3.5 ms from the trigger. Synchrony interneurons (Sy-INs) were non-PreM-Ins that had spike-related features with latencies <3.5 ms in at least one muscle. Unidentified interneurons (U-INs) showed no features in any of the STAs. A total of 572 task-related spinal neurons were studied; 29 cells were MNs, 97 PreM-INs, 32 Sy-INs, and 414 U-INs. MNs were activated predominantly in a tonic fashion during the ramp-and-hold torques and were active in one direction only. The most common response pattern for interneurons, irrespective of their class, was phasic-tonic activity, followed by purely tonic and purely phasic activity. Most interneurons (77%) were bidirectionally active in both flexion and extension. For all classes of interneurons, units with phasic response components tended to be activated first, before torque onset, followed by tonic units. The onset times of PreM-INs relative to onsets of their target muscles were distributed broadly, with a mean of -25 +/- 128 (SD) ms. For most neurons with tonic response components (all MNs, 71% of PreM-INs, 67% of Sy-INs, and 84% of U-INs), activity during the hold period was correlated significantly with the magnitude of static torque exerted by the monkey. The rate-torque regressions generally had positive slopes with higher mean slopes for extension than for flexion. The phasic response components were correlated significantly with rate of change of torque for a smaller percentage of tested PreM-Ins (50%), Sy-INs (83%), and U-INs (77%). In contrast to other premotor neurons [corticomotoneuronal (CM), rubromotoneuronal (RM), and dorsal root ganglion (DRG) afferents] previously characterized under similar conditions, a larger proportion of the spinal PreM-INs were activated after onset of their target muscles, probably reflecting a larger proportion of PreM-INs driven by peripheral input. The rate-torque slopes of PreM-INs tended to be less steep than those of CM and RM cells. Unlike the CM and DRG PreM afferents, which were activated unidirectionally, most spinal PreM-INs showed bidirectional activity, like RM cells.
在三只猕猴执行视觉引导的阶梯跟踪任务并产生等长腕部屈伸扭矩时，记录了C6 - T1脊髓神经元的活动。在≤12块独立的前臂肌肉中记录肌电图活动（EMG）。整流和未整流EMG的触发尖峰平均值（STA）用于将神经元分为四组。运动神经元（MNs）在一块肌肉的未整流STA中具有清晰的尖峰后运动单位特征。运动前中间神经元（PreM - INs）在至少一块肌肉中具有尖峰后效应，触发后的起始潜伏期≥3.5毫秒。同步中间神经元（Sy - INs）是非PreM - INs，在至少一块肌肉中具有潜伏期<3.5毫秒的与尖峰相关的特征。未识别的中间神经元（U - INs）在任何STA中均未显示出特征。总共研究了572个与任务相关的脊髓神经元；29个细胞为MNs，97个PreM - INs，32个Sy - INs和414个U - INs。MNs在斜坡保持扭矩期间主要以紧张性方式被激活，并且仅在一个方向上活跃。中间神经元最常见的反应模式，无论其类别如何，是相位 - 紧张性活动，其次是纯粹的紧张性和纯粹的相位性活动。大多数中间神经元（77%）在屈伸两个方向上均双向活跃。对于所有类别的中间神经元，具有相位反应成分的单位往往在扭矩开始之前首先被激活，然后是紧张性单位。PreM - INs相对于其目标肌肉开始的起始时间分布广泛，平均值为 - 25±128（标准差）毫秒。对于大多数具有紧张性反应成分的神经元（所有MNs，71%的PreM - INs，67%的Sy - INs和84%的U - INs），保持期的活动与猴子施加的静态扭矩大小显著相关。速率 - 扭矩回归通常具有正斜率，伸展的平均斜率高于屈曲。对于较小比例的测试PreM - INs（50%）、Sy - INs（83%）和U - INs（77%），相位反应成分与扭矩变化率显著相关。与先前在类似条件下表征的其他运动前神经元[皮质运动神经元（CM）、红核运动神经元（RM）和背根神经节（DRG）传入纤维]相比，脊髓PreM - INs中有更大比例在其目标肌肉开始后被激活，这可能反映了由外周输入驱动的PreM - INs比例更大。PreM - INs的速率 - 扭矩斜率往往比CM和RM细胞的斜率更平缓。与单向激活的CM和DRG运动前传入纤维不同，大多数脊髓PreM - INs表现出双向活动，类似于RM细胞。
