Little is known about the organizational and functional connectivity of the corticospinal (CS) circuits that are essential for voluntary movement. Here, we map the connectivity between CS neurons in the forelimb motor and sensory cortices and various spinal interneurons, demonstrating that distinct CS-interneuron circuits control specific aspects of skilled movements. CS fibers originating in the mouse motor cortex directly synapse onto premotor interneurons, including those expressing Chx10. Lesions of the motor cortex or silencing of spinal Chx10+ interneurons produces deficits in skilled reaching. In contrast, CS neurons in the sensory cortex do not synapse directly onto premotor interneurons, and they preferentially connect to Vglut3+ spinal interneurons. Lesions to the sensory cortex or inhibition of Vglut3+ interneurons cause deficits in food pellet release movements in goal-oriented tasks. These findings reveal that CS neurons in the motor and sensory cortices differentially control skilled movements through distinct CS-spinal interneuron circuits.
Keywords: Chx10; V2a; Vglut3; corticospinal neuron; motor cortex; motor neuron; sensory cortex; skilled movement; spinal interneuron.
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