Martin J H, 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):429-43. doi: 10.1007/BF00230201.
This study analyzed changes in the performance of a reaching task and its adaptive modification produced by reversible inactivation of three sites within the forelimb representation of the motor cortex (MCx, area 4 gamma) in five cats by microinjections of muscimol. Two sites were located in the lateral MCx, rostral (RL-MCx) and caudal (CL-MCx) to the end of the cruciate sulcus, where intracortical microstimulation (ICMS) produced contraction of the most distal muscles. The third site was located more medially, in the anterior sigmoid gyrus (RM-MCx) where ICMS primarily produced contraction of more proximal muscles. The task required the animals to reach into a horizontal target well, located in front of them at one of three possible heights, to grasp and retrieve a small piece of food. The height of the reach was primarily achieved by elbow flexion. Grasping consisted primarily of digit flexion, and food retrieval consisted of forearm supination and shoulder extension. In some blocks of trials, an obstacle was placed in the path of the limb to assess the animal's ability to adaptively adjust the kinematic characteristics of their response trajectory. In normal animals, contact with the bar on the first trial triggered a corrective response at short latency that allowed the paw to circumvent the bar. On all subsequent trials, the trajectory was adapted to prevent contact with the obstacle, with a safety margin of about 1 cm. Inactivation at all sites produced a slowing of movement, a protracted and extended forelimb posture, and increased variability of initial limb position. In addition, inactivation of RL-MCx immediately produced systematic reaching errors, consisting of hypermetric movements, as well as impaired grasping and food retrieval. The degree of hypermetria was similar for all target heights and was not associated with alterations in trajectory control. During inactivation, animals did not compensate for the hypermetria by reducing paw path elevation, suggesting a defect in kinematic planning or in adaptive control. This was confirmed by finding that trajectory adaptation to avoid bar contact was impaired during RL-MCx inactivation. The short latency corrective response, triggered by contact of the limb with the obstacle was, however, preserved. Inactivation of CL-MCx did not impair aiming, grasping, or adaptation immediately after injection. However, impairments occurred after about 1 h postinjection, and at that time mimicked the effects of RL-MCx inactivation.(ABSTRACT TRUNCATED AT 400 WORDS)
本研究分析了在五只猫的运动皮层（MCx，4γ区）前肢代表区内，通过微量注射蝇蕈醇可逆性失活三个位点后，伸手任务表现的变化及其适应性改变。两个位点位于外侧MCx，在十字沟末端的 rostral（RL-MCx）和 caudal（CL-MCx），皮质内微刺激（ICMS）在此处可引起最远端肌肉收缩。第三个位点位于更内侧的前乙状回（RM-MCx），ICMS在此处主要引起更近端肌肉收缩。该任务要求动物伸手进入位于它们前方三个可能高度之一的水平目标孔，抓取并取回一小块食物。伸手的高度主要通过肘部弯曲来实现。抓取主要包括手指弯曲，取回食物包括前臂旋后和肩部伸展。在一些试验块中，在肢体路径上放置一个障碍物，以评估动物自适应调整其反应轨迹运动学特征的能力。在正常动物中，第一次试验时与横杆接触会触发短潜伏期的纠正反应，使爪子能够绕过横杆。在所有后续试验中，轨迹会进行调整以防止与障碍物接触，安全距离约为1厘米。所有位点失活均导致运动减慢以及前肢姿势延长和伸展，并且初始肢体位置的变异性增加。此外，RL-MCx失活立即产生系统性的伸手误差，包括动作过度，以及抓握和食物取回受损。所有目标高度的动作过度程度相似，并且与轨迹控制的改变无关。在失活期间，动物没有通过降低爪子路径高度来补偿动作过度，这表明在运动学规划或自适应控制方面存在缺陷。这一点通过发现在RL-MCx失活期间，避免横杆接触的轨迹适应性受损得到了证实。然而，由肢体与障碍物接触触发的短潜伏期纠正反应得以保留。CL-MCx失活在注射后立即不会损害瞄准、抓握或适应性。然而，在注射后约1小时出现损伤，此时模拟了RL-MCx失活的影响。（摘要截断于400字）
