Galea M P, Darian-Smith I
Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Australia.
J Comp Neurol. 1997 May 12;381(3):307-19.
The macaque recovers quite rapidly from the immediate severe flaccid hemiparesis that results from unilateral section of the cervical spinal cord (between C3 and C6) and starts to use the impaired hand to pick up objects within about 30 days following the surgery. Within another 60 days, the monkey is quite dexterous; nonetheless, there is a persisting deficit. We used video recording to study the long-term recovery of manual dexterity following unilateral section of the cervical cord in newborn and juvenile monkeys. A reach-and-retrieve manual task was examined. By using a preset oppositional force, opposition of the pads of the index finger and thumb in the vertical plane was needed to retrieve the desired target object. The corticospinal connectivity of each monkey was also examined by using retrograde or anterograde tracers at the end of the experimental period (Galea and Darian-Smith [1997] J. Comp. Neurol., this issue) and was correlated with the manual performance. Manually retrieving an object depends on the coordination of several control processes acting in parallel, including 1) visually guided components, such as directing the arm toward the object, aligning the digits with the target object by pronating the forearm, and preshaping the index/thumb separation to match with the size and shape of the target, and 2) manipulative components that depend on tactual input and that also include independent movements of the digits and the application of the appropriate oppositional forces. The impairment of manual dexterity that persisted after a cervical section, although it was small, involved these processes and was evident in 1) the less direct trajectory used in reaching, 2) the loss of preshaping of the separated index finger and thumb prior to grasping the target object, and 3) a weakening of the oppositional forces that could be developed between the pads of the index finger and thumb. Although, in the accompanying paper, we did not preclude some regeneration of severed corticospinal connections, we did show that, if any such reconstruction occurred, then it was limited. The remarkable but incomplete recovery of dexterity over a period of 6-12 months, therefore, must be achieved by 1) optimizing the transmission of information from the cortex to the spinal cord by the substantially reduced populations of corticospinal neurons and corticobulbospinal projections and/or 2) the effective use of spinal circuitry in regulating the more stereotyped elements of the manual task.
猕猴在因单侧切断颈脊髓（C3至C6之间）而导致的即刻严重弛缓性偏瘫后恢复相当迅速，并且在手术后约30天内开始使用受损的手拿起物体。在另外60天内，猴子变得相当灵巧；尽管如此，仍存在持续的功能缺陷。我们使用视频记录来研究新生和幼年猕猴单侧切断颈脊髓后手灵巧性的长期恢复情况。对一项伸手抓取的手动任务进行了检查。通过使用预设的对抗力，需要食指和拇指指腹在垂直平面上进行对掌动作以抓取所需目标物体。在实验期结束时，还通过使用逆行或顺行示踪剂检查了每只猴子的皮质脊髓连接性（Galea和Darian-Smith [1997]《比较神经学杂志》，本期），并将其与手动操作表现相关联。手动抓取物体取决于多个并行作用的控制过程的协调，包括1）视觉引导成分，如将手臂指向物体、通过旋前前臂使手指与目标物体对齐，以及预先调整食指/拇指间距以匹配目标物体的大小和形状，以及2）依赖触觉输入的操作成分，这也包括手指的独立运动和施加适当的对抗力。颈髓切断后持续存在的手灵巧性损伤虽然较小，但涉及这些过程，并且在以下方面很明显：1）伸手时使用的轨迹不那么直接，2）在抓取目标物体之前分离的食指和拇指失去预先塑形，以及3）食指和拇指指腹之间可产生的对抗力减弱。尽管在随附的论文中，我们没有排除切断的皮质脊髓连接有一些再生的可能性，但我们确实表明，如果发生任何此类重建，那么也是有限的。因此，在6至12个月的时间内灵巧性的显著但不完全恢复，必定是通过1）由大量减少的皮质脊髓神经元和皮质延髓脊髓投射来优化从皮质到脊髓的信息传递，和/或2）有效利用脊髓回路来调节手动任务中更刻板的要素而实现的。
