Highlights
- •In mice, motor cortex is required for a trained forelimb task, but not walking
- •Motor cortex activates short-latency effector pathways only during the trained task
- •Distinct weighted sums of motor cortical firing patterns vary strongly in each task
- •This change could permit motor cortex to engage short-latency pathways differentially
Summary
Blocking
motor cortical output with lesions or pharmacological inactivation has
identified movements that require motor cortex. Yet, when and how motor
cortex influences muscle activity during movement execution remains
unresolved. We addressed this ambiguity using measurement and
perturbation of motor cortical activity together with electromyography
in mice during two forelimb movements that differ in their requirement
for cortical involvement. Rapid optogenetic silencing and electrical
stimulation indicated that short-latency pathways linking motor cortex
with spinal motor neurons are selectively activated during one behavior.
Analysis of motor cortical activity revealed a dramatic change between
behaviors in the coordination of firing patterns across neurons that
could account for this differential influence. Thus, our results suggest
that changes in motor cortical output patterns enable a behaviorally
selective engagement of short-latency effector pathways. The model of
motor cortical influence implied by our findings helps reconcile
previous observations on the function of motor cortex.
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