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Physiological changes underlying bilateral isometric arm voluntary contractions in healthy humans
Demetris S Soteropoulos1, Monica A Perez
1Institute of Neuroscience, Medical School, Newcastle University, Newcastle upon Tyne, United Kingdom.
Journal of Neurophysiology
|January 29, 2011
Summary
Bilateral arm muscle activation affects motor cortex output differently depending on whether distal or proximal muscles are engaged. Simultaneous distal and proximal arm muscle activity shows weaker transcallosal inhibition than distal-only activation.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Bilateral motor tasks often involve simultaneous activation of distal and proximal arm muscles.
- The physiological interactions between these muscle groups during such tasks are not well understood.
Purpose of the Study:
- To investigate the interactions between contralateral motor cortex output and simultaneous activation of ipsilateral distal and proximal arm muscles.
- To examine interhemispheric inhibition and short-interval intracortical inhibition during various bilateral contraction conditions.
Main Methods:
- Used transcranial magnetic stimulation (TMS) to measure motor-evoked potentials (MEPs) in the left first dorsal interosseous (FDI) muscle.
- Assessed interhemispheric inhibition (IHI) at 10 and 40 ms and short-interval intracortical inhibition (SICI).
- Participants performed isometric index finger abduction while the contralateral limb performed voluntary contractions with FDI, biceps, triceps, or tibialis anterior.
Main Results:
- Left FDI MEPs were suppressed during contralateral FDI, biceps, and triceps contraction, but not tibialis anterior contraction.
- Interhemispheric inhibition (IHI) was reduced during simultaneous distal-proximal arm muscle activation compared to bilateral distal muscle activation.
- Short-interval intracortical inhibition (SICI) increased with distal-proximal arm muscle activation and decreased with bilateral distal muscle activation.
Conclusions:
- Isometric voluntary contraction of distal or proximal arm muscles, but not a foot muscle, decreases contralateral finger muscle corticospinal output.
- Transcallosal inhibition is stronger during bilateral distal hand muscle activation than during distal-proximal arm muscle activation.
- GABAergic intracortical activity is modulated oppositely to transcallosal inhibition, suggesting distinct neural mechanisms for different bilateral activation patterns.
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