A distinct neural activity subspace for direct motor cortical influence on muscles

Abstract

Among the patterns of motor cortical activity, those that directly drive muscles remain unresolved. Lesion studies have led to the hypothesis that motor cortex functions primarily to improve movement efficacy by enabling patterns of muscle activity that the rest of the motor system cannot achieve1–3. Yet such studies weakly constrain when motor cortical output influences muscle activity in the unperturbed state. Analysis of motor cortical activity has consistently found, and imputed functional significance upon, signals that correlate with limb muscle activity4–6or kinematics7–9. But a selective role in driving certain muscle activity patterns might rely on signals related only to those patterns and not others. Here we quantified the direct influence of forelimb motor cortex on muscle activity throughout a naturalistic climbing behavior, finding that this influence is selective for, and highly dependent upon, muscle activity states. We used multielectrode array recordings to identify linear combinations (components) of motor cortical activity patterns that covary with this influence. We find that these components differ substantially from those that covary with muscle activity or kinematics. Our results reveal a direct motor cortical influence on muscles that is selective within a motor behavior and reliant on a previously undescribed neural activity subspace.