Corticospinal excitability is modulated by distinct movement patterns during action observation

Area of Science:

• Neuroscience
• Motor Control
• Cognitive Neuroscience

Background:

• Primary motor cortex excitability increases during action observation.
• The precise modulation of motor cortex excitability for actions with varying complexity is not fully understood.

Purpose of the Study:

• To investigate time-dependent changes in corticospinal excitability during the observation of two distinct actions: pointing and reach-and-grasp.
• To compare neural engagement patterns associated with different movement complexities.

Main Methods:

• Utilized single-pulse transcranial magnetic stimulation (TMS) to assess primary motor cortex excitability.
• Recorded motor evoked potentials (MEP) from intrinsic hand muscles (first dorsal interosseous and abductor digiti minimi).
• Compared MEPs during observation of static hands versus dynamic pointing and grasping actions.

Main Results:

• No significant difference in MEP amplitude was observed between static hand observation and action observation.
• Early in the movement (index finger extension), MEP amplitude in the first dorsal interosseous was greater during pointing observation compared to grasping.
• Later in the movement (hand opening for grasp), MEP amplitude in the first dorsal interosseous was greater during grasping observation compared to pointing.

Conclusions:

• Primary motor cortex excitability is differentially modulated during the observation of pointing versus grasping actions.
• These findings suggest the action observation network is engaged in a time-dependent manner, reflecting movement complexity.