Evidence that distinct human primary motor cortex circuits control discrete and rhythmic movements

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Human movements are composed of discrete and rhythmic actions.
• Previous research suggests different neural control mechanisms for discrete movements (DM) and rhythmic movements (RM).
• The specific contributions of human motor cortex circuits to DM and RM are not fully understood.

Purpose of the Study:

• To investigate how distinct primary motor cortex and corticospinal circuits differ in excitability between DM and RM.
• To determine if these differences are phase-specific during movement.

Main Methods:

• Subjects performed wrist flexion for either DM or RM.
• Transcranial magnetic stimulation and peripheral nerve stimulation were used to assess neural circuit excitability.
• Excitability was probed at movement initiation (MI) and movement execution (ME).

Main Results:

• Supragranular layer excitability was higher during DM at MI.
• More complex corticospinal circuit excitability was lower during DM than RM at ME.
• No task-specific differences were observed for infragranular layer output neurons.
• Differences persisted between ongoing and the final cycle of RM.

Conclusions:

• Evidence supports distinct motor cortex circuit engagement for DM and RM.
• These findings highlight specific neural control mechanisms underlying different movement types.
• The observed differences are intrinsic to the movement type, not solely explained by kinematics.