BACKGROUND The cerebellum and primary motor cortex (M1) are crucial to coordinated and accurate movements of the upper limbs. There is also appreciable evidence that these two structures exert somewhat divergent influences upon proximal versus distal upper limb control. Here, we aimed to differentially regulate the contribution of the cerebellum and M1 to proximal and distal effectors during motor adaptation, with transcranial direct current stimulation (tDCS). For this, we employed tasks that promote similar motor demands, but isolate whole arm from hand/finger movements, in order to functionally segregate the hierarchy of upper limb control. METHODS Both young and older adults took part in a visuomotor rotation task; where they adapted to a 60° visuomotor rotation using either a hand-held joystick (requiring finger/hand movements) or a 2D robotic manipulandum (requiring whole-arm reaching movements), while M1, cerebellar or sham tDCS was applied. RESULTS We found that cerebellar stimulation improved adaptation performance when arm movements were required to complete the task, while in contrast stimulation of M1 enhanced adaptation during hand and finger movements only. This double-dissociation was replicated in an independent group of older adults, demonstrating that the behaviour remains intact in ageing. CONCLUSIONS These results suggest that stimulation of distinct motor areas can selectively improve motor adaptation in the proximal and distal upper limb. This also highlights new ways in which tDCS might be best applied to achieve reliable rehabilitation of upper limb motor deficits.

中文翻译：

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靶向 tDCS 选择性地改善近端和远端上肢的运动适应

背景技术小脑和初级运动皮层 (M1) 对于上肢的协调和准确运动至关重要。还有明显的证据表明，这两种结构对近端和远端上肢控制的影响有些不同。在这里，我们旨在通过经颅直流电刺激 (tDCS)，在运动适应过程中差异调节小脑和 M1 对近端和远端效应器的贡献。为此，我们采用了促进类似运动需求的任务，但将整个手臂与手/手指运动隔离开来，以便在功能上隔离上肢控制的层次结构。方法 年轻人和老年人都参加了视觉运动旋转任务；他们使用手持式操纵杆（需要手指/手部运动）或 2D 机器人操纵器（需要全臂伸展运动）适应 60° 视觉运动旋转，同时应用 M1、小脑或假 tDCS。结果 我们发现，当需要手臂运动来完成任务时，小脑刺激可以改善适应性能，而相比之下，M1 刺激仅在手和手指运动期间增强适应性。这种双重解离在一个独立的老年人群中被复制，表明这种行为在衰老过程中保持不变。结论 这些结果表明，刺激不同的运动区域可以选择性地改善近端和远端上肢的运动适应。