Department of Molecular and Integrative Physiology and Landon Center on Aging, Kansas University Medical Center, Kansas City, KS, USA.
J Neurophysiol. 2013 Mar;109(5):1268-82. doi: 10.1152/jn.00044.2012. Epub 2012 Dec 12.
Primary motor cortex (M1) movement representations reflect acquired motor skills. Representations of muscles and joints used in a skilled task expand. However, it is unknown whether motor restriction in healthy individuals results in complementary reductions in M1 representations. With the use of intracortical microstimulation techniques in squirrel monkeys, detailed maps of movement representations in M1 were derived before and up to 35 wk after restriction of the preferred distal forelimb (DFL) by use of a soft cast. Although total DFL area and movement threshold remained constant, casting resulted in a redistribution of digit and wrist/forearm representations. Digit representations progressively decreased, whereas wrist/forearm representations progressively increased in areal extent. In three of four monkeys, hand preference returned to normal by the end of the postcast recovery period, and postrecovery maps demonstrated reversal of restriction-induced changes. However, in one monkey, a chronic motor impairment occurred in the casted limb. Rehabilitation via a forced-use paradigm resulted in recovery in use and skill of the impaired limb, as well as restoration of normal motor maps. These results demonstrate that plasticity in motor representations can be induced by training or restricting movements of the limb. Physiological changes induced by restriction appear to be reversible, even in the case of adverse motor outcomes. The respective contributions of both disuse and lost motor skills are discussed. These results have relevance for clinical conditions requiring forelimb casting as well as interpreting the differential effects of injury and disuse that are necessarily intertwined after cortical injury, as occurs in stroke.
初级运动皮层（M1）的运动代表反映了后天习得的运动技能。在熟练任务中使用的肌肉和关节的代表区域会扩大。然而，目前尚不清楚健康个体的运动限制是否会导致 M1 代表区域的互补性减少。在松鼠猴中使用皮质内微刺激技术，在使用软石膏限制首选远端前肢（DFL）之前和之后长达 35 周，得出了 M1 运动代表的详细图谱。尽管 DFL 区域的总面积和运动阈值保持不变，但铸造导致了数字和腕/前臂代表区域的重新分配。数字代表区域逐渐减小，而腕/前臂代表区域的区域逐渐增加。在四只猴子中的三只中，到了后铸恢复期结束时，手的偏好恢复正常，并且恢复后的图谱显示出限制诱导变化的逆转。然而，在一只猴子中，铸造肢体发生了慢性运动障碍。通过强制使用范式进行康复治疗，导致受损肢体的使用和技能恢复正常，运动图谱也得到了恢复。这些结果表明，运动代表的可塑性可以通过训练或限制肢体的运动来诱导。限制引起的生理变化似乎是可逆的，即使在运动障碍的不良结果情况下也是如此。讨论了两者的各自贡献，即废用和丧失运动技能。这些结果与需要前肢铸造的临床情况有关，也与皮质损伤后必然交织在一起的损伤和废用的不同影响有关，例如中风。
