Speed-dependent contribution of callosal pathways to ipsilateral movements

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Transcallosal inhibition between primary motor cortices is crucial for suppressing unwanted limb movements during contralateral activation.
• The specific role of transcallosal inhibition in voluntary movements of the active limb is not fully understood.

Purpose of the Study:

• To investigate the functional contribution of transcallosal inhibition during the preparation and execution of self-paced and ballistic ipsilateral movements.
• To examine how movement speed influences transcallosal inhibitory pathways.

Main Methods:

• Transcranial magnetic stimulation (TMS) was used to measure interhemispheric inhibition (IHI) and ipsilateral silent period (iSP).
• Participants performed self-paced and ballistic index finger abduction and elbow flexion movements.
• Measurements were taken during preparatory and execution phases relative to rest.

Main Results:

• Interhemispheric inhibition (IHI) decreased during the preparatory phase for both self-paced and ballistic movements, with a greater decrease for ballistic movements.
• In the execution phase, IHI and ipsilateral silent period (iSP) increased for ballistic compared to self-paced movements.
• Transcallosal inhibition showed negative correlation with reaction times and positive correlation with movement amplitude.

Conclusions:

• Transcallosal inhibition significantly contributes to ipsilateral movements across different speeds, particularly during rapid actions.
• Decreased transcallosal inhibition in the preparatory phase may facilitate rapid movement initiation.
• Increased transcallosal inhibition in the execution phase might aid in movement cessation, with amplified effects at higher speeds.