Primary motor cortex (M1) almost exclusively controls the contralateral side of the body. However, M1 activity is also modulated during ipsilateral body movements. Previous work has shown that M1 activity related to the ipsilateral arm is independent of the M1 activity related to the contralateral arm. How do these patterns of activity interact when both arms move simultaneously? We explored this problem by training 2 monkeys (male, Macaca mulatta) in a postural perturbation task while recording from M1. Loads were applied to one arm at a time (unimanual) or both arms simultaneously (bimanual). We found 83% of neurons (n = 236) were responsive to both the unimanual and bimanual loads. We also observed a small reduction in activity magnitude during the bimanual loads for both limbs (25%). Across the unimanual and bimanual loads, neurons largely maintained their preferred load directions. However, there was a larger change in the preferred loads for the ipsilateral limb (~25%) than the contralateral limb (~9%). Lastly, we identified the contralateral and ipsilateral subspaces during the unimanual loads and found they captured a significant amount of the variance during the bimanual loads. However, the subspace captured more of the bimanual variance related to the contralateral limb (97%) than the ipsilateral limb (66%). Our results highlight that, even during bimanual motor actions, M1 largely retains its representations of the contralateral and ipsilateral limbs.

SIGNIFICANCE STATEMENT Previous work has shown that primary motor cortex (M1) represents information related to the contralateral limb, its downstream target, but also reflects information related to the ipsilateral limb. Can M1 still represent both sources of information when performing simultaneous movements of the limbs? Here we record from M1 during a postural perturbation task. We show that activity related to the contralateral limb is maintained between unimanual and bimanual motor actions, whereas the activity related to the ipsilateral limb undergoes a small change between unimanual and bimanual motor actions. Our results indicate that two independent representations can be maintained and expressed simultaneously in M1.

初级运动皮层（M1）几乎完全控制身体的对侧。但是，在同侧身体运动过程中，M1的活性也受到调节​​。先前的研究表明，与同侧手臂相关的M1活动独立于与对侧手臂相关的M1活动。当两只手臂同时运动时，这些活动模式如何相互作用？我们通过训练2只猴子（雄性，猕猴，Macaca mulatta）在姿势摄动任务中（同时从M1记录）来探讨了这个问题。一次（一只手）或一只手臂同时（两只手）施加载荷。我们发现神经元的83％（ñ= 236）对单手和双手负载都做出了响应。我们还观察到双手的双肢负荷期间活动量略有降低（25％）。跨单手和双手负载，神经元在很大程度上维持了其首选的负载方向。但是，同侧肢（〜25％）比对侧肢（〜9％）的首选负荷有较大变化。最后，我们确定了单手载荷过程中的对侧和同侧子空间，发现它们在双手载荷过程中捕获了大量的方差。但是，与同侧肢体（66％）相比，子空间捕获了更多与对侧肢体有关的双侧方差（97％）。我们的结果表明，即使在双手运动时，M1仍会保留其对侧和同侧肢体的表示。

意义声明先前的研究表明，初级运动皮层（M1）代表与对侧肢体有关的信息，即其下游目标，但也反映了与同侧肢体有关的信息。在同时进行肢体运动时，M1还能代表两个信息源吗？在这里，我们在姿势摄动任务期间从M1记录。我们表明，与对侧肢体有关的活动在单手和双手运动之间保持不变，而与同侧肢体有关的活动在单手和双手运动之间发生小的变化。我们的结果表明，可以在M1中同时维护和表达两个独立的表示形式。