The organization and functional logic of corticospinal motor neurons and their target connections remains unclear, despite their evident influence on movement. Spinal interneurons mediate much of this influence, yet we know little about the way in which corticospinal neurons engage spinal interneurons. This is perhaps not surprising given that the principles of organization of local spinal microcircuits remain elusive--we have glimpses of an underlying order but lack a comprehensive view of their functional architecture. In this brief essay we make a case that a new focus on the intersection of cortical and spinal circuits may provide clarity to the interpretation of corticospinal motor neuron firing patterns and help specify the logic of corticospinal motor neuronal function.
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