Greater task difficulty during unilateral motor tasks changes intracortical inhibition and facilitation in the ipsilateral primary motor cortex in young men

Neurosci Lett. 2023 Jun 21;808:137293. doi: 10.1016/j.neulet.2023.137293. Epub 2023 May 9.


This study aimed to clarify the changes in short-interval intracortical inhibition (SICI) and facilitation (ICF) in the ipsilateral primary motor cortex (iM1) when the task difficulty during unilateral force-matching tasks was manipulated. Twelve young male adults matched their left index finger abduction force to a displayed target force. Task difficulty was manipulated by varying the acceptable force range of the mean target force (5% MVC). Briefly, unilateral force-matching tasks with lesser and greater task difficulty (EASY and DIFF, respectively) were assigned acceptable force ranges of ± 7% and ± 0% of the target force, respectively. To evaluate SICI and ICF in iM1, paired-pulse transcranial magnetic stimulation with 2-ms and 10-ms interstimulus intervals was applied to correct motor-evoked potentials (MEPs) from the first dorsal interosseous muscle during each task. Test stimulus intensity to evoke the MEP with a peak-to-peak amplitude of approximately 0.5-1.5 mV for each task was lower in DIFF than in EASY (P = 0.001), indicating that DIFF increased corticospinal excitability of the ipsilateral hemisphere compared with EASY. The MEPs in SICI and ICF were significantly larger in DIFF than in EASY (P < 0.050). These results suggest that greater corticospinal excitability in the ipsilateral hemisphere during DIFF is associated with reduced SICI and increased ICF.

Keywords: Force-matching task; Index finger abduction force; Intracortical excitability; Motor-evoked potential; Paired-pulse transcranial magnetic stimulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Electromyography / methods
  • Evoked Potentials, Motor / physiology
  • Fingers
  • Humans
  • Male
  • Motor Cortex* / physiology
  • Muscle, Skeletal / physiology
  • Neural Inhibition / physiology
  • Transcranial Magnetic Stimulation / methods