Cunningham David A, Roelle Sarah M, Allexandre Didier, Potter-Baker Kelsey A, Sankarasubramanian Vishwanath, Knutson Jayme S, Yue Guang H, Machado Andre G, Plow Ela B
Human Performance and Engineering Research, Kessler Foundation, West Orange, NJ, USA.
Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Ave, ND20, Cleveland, OH, 44195, USA.
Exp Brain Res. 2017 Apr;235(4):1097-1105. doi: 10.1007/s00221-016-4867-2. Epub 2017 Jan 16.
Motor overflow, typically described in the context of unimanual movements, refers to the natural tendency for a 'resting' limb to move during movement of the opposite limb and is thought to be influenced by inter-hemispheric interactions and intra-cortical networks within the 'resting' hemisphere. It is currently unknown, however, how motor overflow contributes to asymmetric force coordination task accuracy, referred to as bimanual interference, as there is need to generate unequal forces and corticospinal output for each limb. Here, we assessed motor overflow via motor evoked potentials (MEPs) and the regulation of motor overflow via inter-hemispheric inhibition (IHI) and short-intra-cortical inhibition (SICI) using transcranial magnetic stimulation in the presence of unimanual and bimanual isometric force production. All outcomes were measured in the left first dorsal interosseous (test hand) muscle, which maintained 30% maximal voluntary contraction (MVC), while the right hand (conditioning hand) was maintained at rest, 10, 30, or 70% of its MVC. We have found that as higher forces are generated with the conditioning hand, MEP amplitudes at the active test hand decreased and inter-hemispheric inhibition increased, suggesting reduced motor overflow in the presence of bimanual asymmetric forces. Furthermore, we found that subjects with less motor overflow (i.e., reduced MEP amplitudes in the test hemisphere) demonstrated poorer accuracy in maintaining 30% MVC across all conditions. These findings suggest that motor overflow may serve as an adaptive substrate to support bimanual asymmetric force coordination.
运动溢出通常是在单手运动的背景下描述的，指的是在对侧肢体运动时“静止”肢体自然产生运动的倾向，并且被认为受“静止”半球内的半球间相互作用和皮质内神经网络的影响。然而，目前尚不清楚运动溢出如何影响非对称力协调任务的准确性，即双手干扰，因为每个肢体需要产生不等的力和皮质脊髓输出。在这里，我们在单手和双手等长力产生的情况下，通过运动诱发电位（MEP）评估运动溢出，并使用经颅磁刺激通过半球间抑制（IHI）和短皮质内抑制（SICI）评估运动溢出的调节。所有结果均在左侧第一背侧骨间肌（测试手）中测量，该肌肉保持30%的最大自主收缩（MVC），而右手（调节手）保持在休息状态、其MVC的10%、30%或70%。我们发现，随着调节手产生更大的力，活动测试手的MEP幅度降低，半球间抑制增加，这表明在双手非对称力存在的情况下运动溢出减少。此外，我们发现运动溢出较少的受试者（即测试半球的MEP幅度降低）在所有条件下保持30%MVC时表现出较差的准确性。这些发现表明，运动溢出可能作为一种适应性基质来支持双手非对称力协调。
