Behaviorally Selective Engagement of Short-Latency Effector Pathways by Motor Cortex

Area of Science:

• Neuroscience
• Motor Control
• Systems Neuroscience

Background:

• The precise role of the motor cortex in controlling muscle activity during movement execution remains unclear.
• Previous studies using inactivation methods have identified movements dependent on motor cortex but not the timing or mechanism of its influence.

Purpose of the Study:

• To investigate how and when the motor cortex influences muscle activity during different forelimb movements in mice.
• To determine the neural mechanisms underlying the selective engagement of motor cortical pathways during behavior.

Main Methods:

• Combined optogenetic manipulation (silencing and stimulation) of motor cortex with electromyography (EMG) in mice.
• Recorded and analyzed motor cortical neuronal activity during two distinct forelimb behaviors with differing cortical involvement.
• Perturbed motor cortical output to assess its causal role in movement execution.

Main Results:

• Short-latency pathways connecting the motor cortex to spinal motor neurons were selectively activated during one of the two tested behaviors.
• Significant changes in the coordination of neuronal firing patterns within the motor cortex were observed between the two behaviors.
• Optogenetic silencing and stimulation revealed a behavior-dependent modulation of motor cortical influence on muscle activity.

Conclusions:

• Changes in motor cortical output firing patterns are crucial for behaviorally selective engagement of direct motor pathways.
• This study provides a model for understanding motor cortical function that reconciles previous, seemingly contradictory findings.
• Motor cortex dynamically adjusts its output to control specific muscle synergies based on behavioral demands.