Romei Vincenzo, Thut Gregor, Ramos-Estebanez Ciro, Pascual-Leone Alvaro
Berenson-Allen Center for Noninvasive Brain Stimulation, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA, USA.
Cortex. 2009 Oct;45(9):1058-64. doi: 10.1016/j.cortex.2009.01.003. Epub 2009 Feb 5.
Procedural skills consist of several components that can be simultaneously acquired. During a motor-learning task we can distinguish between how a "movement" is performed (intrinsic component) and the spatial-related (extrinsic) component of this movement. The intrinsic movement component is thought to be supported by motor loops, including primary motor cortex (M1) as assessed with neuroimaging studies. Here we want to test further whether M1 makes a critical contribution to the movement rather than spatial-related component of skill-learning. To this purpose, we used repetitive Transcranial Magnetic Stimulation (rTMS) and the serial reaction time (SRT) task. Twenty right-handed participants performed the SRT-task starting with their left or right hand. After this learning session, participants switched to the untrained hand by performing original (spatial-related) and mirror-ordered (movement-based) sequences. rTMS was applied to M1 ipsi- or contralateral to the transfer-hand and both sequences were retested. Results revealed rTMS-interference with motor-skill transfer of mirror-ordered but not original sequences, showing that M1 is critically involved in the retrieval/transformation of the intrinsic but not the extrinsic movement coordinates. rTMS-interference in the mirror-condition consisted of both (i) disruption and (ii) release of motor-skill transfer depending on the stimulated hemisphere and on transfer-hand. The pattern of results suggests (i) contralateral (right) M1 involvement in retrieval/transformation of motor information during left-hand reproduction of previously acquired right-hand motor-skills; and (ii) modulatory interactions of inhibitory nature from the dominant (left) to the non-dominant (right) M1 in the same transfer-condition. These results provide further evidence that M1 is essential to intrinsic movement-based skill-learning and novel insight on models of motor-learning and hemispheric specialization, suggesting the involvement of interhemispheric inhibition.
程序性技能由几个可以同时习得的组成部分构成。在一项运动学习任务中，我们可以区分“动作”的执行方式（内在组成部分）和该动作的空间相关（外在）组成部分。内在动作组成部分被认为由运动环路支持，包括经神经影像学研究评估的初级运动皮层（M1）。在此，我们想进一步测试M1对技能学习的动作部分而非空间相关部分是否有关键贡献。为此，我们使用了重复经颅磁刺激（rTMS）和序列反应时（SRT）任务。20名右利手参与者用左手或右手开始执行SRT任务。在这个学习阶段之后，参与者通过执行原始（空间相关）和镜像顺序（基于动作）序列切换到未训练的手。rTMS应用于与转换手同侧或对侧的M1，然后对两个序列进行重新测试。结果显示rTMS干扰了镜像顺序序列的运动技能转换，但未干扰原始序列，表明M1关键参与内在而非外在动作坐标的提取/转换。镜像条件下的rTMS干扰包括（i）破坏和（ii）根据受刺激半球和转换手释放运动技能转换。结果模式表明（i）在先前习得的右手运动技能的左手再现过程中，对侧（右侧）M1参与运动信息的提取/转换；以及（ii）在相同转换条件下，从优势（左侧）M1到非优势（右侧）M1存在抑制性的调节性相互作用。这些结果进一步证明M1对基于内在动作的技能学习至关重要，并为运动学习和半球特化模型提供了新的见解，提示了半球间抑制的参与。
