Martin J H, Cooper S E, Ghez C
Center for Neurobiology and Behavior, New York State Psychiatric Institute, College of Physicians and Surgeons, Columbia University, NY 10032.
Exp Brain Res. 1993;94(3):418-28. doi: 10.1007/BF00230200.
This study examined changes in the performance of a single-joint, elbow task produced by reversible inactivation of local regions within the proximal forelimb representation in area 4 gamma of motor cortex (MCx) and the red nucleus (RN) of the cat. Inactivation was carried out by microinjecting lidocaine, gamma-aminobutyric acid, or muscimol into sites where microstimulation evoked contraction of elbow muscles. Reaction time, amplitude, and speed (velocity or dF/dt) of position and force responses elicited during inactivation were compared to control values obtained immediately prior to inactivation. In addition, we assessed qualitatively the effects of inactivation on reaching, placing reactions, and proprioceptive responses to imposed limb displacement. In the single-joint task, injections in MCx did not increase reaction time (simple or choice) and produced modest and inconsistent reductions in response amplitude (mean -8%) and speed (mean -19%). In contrast, injections of the same amounts of inactivating agents in the forelimb representation of RN consistently increased reaction time (34.4%), and increased the reaction time coefficient of variability (32%). There were small reductions in response amplitude (-4%) and speed (-10%) which were less than those produced by MCx inactivation. During reaching, however, these same injections in MCx and RN produced a substantial loss of accuracy. For MCx, this was due, in part, to systematic hypometria: for RN, inaccuracy resulted from increased variability in paw paths. Placing reactions and corrective responses to imposed limb displacements were also depressed by the cortical and rubral injections. Our results suggest that the forelimb representation in RN plays a role in the initiation of the single-joint, elbow tracking response examined here. The RN may mediate cerebellar regulation of response timing, a function that is likely to be important for interjoint coordination. Although neurons in the forelimb representations of MCx may contribute to force generation in single-joint movements, their contribution to multijoint control appears to be more important and is examined in the subsequent report (Martin and Ghez 1993).
本研究检测了猫运动皮层（MCx）4γ区和红核（RN）近端前肢代表区内局部区域可逆性失活所产生的单关节肘部任务表现的变化。通过将利多卡因、γ-氨基丁酸或蝇蕈醇微量注射到微刺激诱发肘部肌肉收缩的部位来实现失活。将失活期间引发的位置和力反应的反应时间、幅度和速度（速度或dF/dt）与失活前立即获得的对照值进行比较。此外，我们定性评估了失活对伸手、放置反应以及对施加的肢体位移的本体感觉反应的影响。在单关节任务中，向MCx注射未增加反应时间（简单或选择反应时间），并使反应幅度（平均-8%）和速度（平均-19%）出现适度且不一致的降低。相比之下，在RN的前肢代表区注射相同量的失活剂会持续增加反应时间（34.4%），并增加反应时间变异系数（32%）。反应幅度（-4%）和速度（-10%）有小幅降低，小于MCx失活所产生的降低幅度。然而，在伸手过程中，在MCx和RN进行的这些相同注射导致准确性大幅下降。对于MCx，这部分是由于系统性的运动不足：对于RN，不准确是由于爪路径的变异性增加所致。皮层和红核注射也会抑制放置反应和对施加的肢体位移的校正反应。我们的结果表明，RN中的前肢代表区在此处检测的单关节肘部跟踪反应的启动中起作用。RN可能介导小脑对反应时间的调节，这一功能可能对关节间协调很重要。尽管MCx前肢代表区的神经元可能有助于单关节运动中的力产生，但其对多关节控制的贡献似乎更重要，并在后续报告中进行了研究（Martin和Ghez，1993）。
