The Task at Hand: Fatigue-Associated Changes in Cortical Excitability during Writing

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Transcranial magnetic stimulation (TMS) measures corticospinal excitability (CSE).
• CSE assessment is task-dependent, influencing results.
• Understanding CSE during natural movements like writing is crucial.

Purpose of the Study:

• To compare fatigue-induced changes in CSE during a natural motor task (hand-writing) versus a conventional laboratory task (isometric finger abduction).
• To investigate if CSE changes measured during writing reflect those during isometric abduction.

Main Methods:

• Assessed single- and paired-pulse motor evoked potentials (MEPs) from the first dorsal interosseous (FDI) muscle.
• Participants underwent a fatigue protocol (submaximal isometric contractions).
• CSE was measured before and after fatigue during either a writing task or an isometric finger abduction task.

Main Results:

• MEP amplitude showed greater variability during writing compared to isometric abduction.
• A significant interaction revealed that fatigue increased intracortical facilitation in printers but not cursive writers during writing.
• No significant changes in intracortical facilitation were observed during the isometric abduction task.

Conclusions:

• This is the first study to assess CSE during hand-writing.
• Fatigue-induced changes in intracortical facilitation are task-dependent.
• Consideration of the motor task during TMS is essential for applying findings to real-world movements.