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Physiological processes influencing motor-evoked potential duration with voluntary contraction
Mehdi A J van den Bos1, Nimeshan Geevasinga1, Parvathi Menon1,2
1Sydney Medical School, University of Sydney, Sydney, Australia.
Journal of Neurophysiology
|December 30, 2016
Summary
Voluntary muscle contraction prolongs motor-evoked potential (MEP) duration and increases amplitude. This MEP duration increase is linked to short-interval intracortical inhibition, suggesting cortical mechanisms contribute to MEP changes during muscle activation.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Voluntary muscle contraction influences motor-evoked potentials (MEPs), affecting their amplitude, latency, and duration.
- While spinal motoneuron excitability and corticospinal volleys explain amplitude and latency changes, the prolonged MEP duration suggests a role for propriospinal interneurons.
- The precise physiological mechanisms underlying MEP duration changes during voluntary contraction require further investigation.
Purpose of the Study:
- To investigate the physiological processes responsible for the prolongation of motor-evoked potential (MEP) duration during voluntary muscle contraction.
- To explore the relationship between MEP duration, MEP amplitude, and short-interval intracortical inhibition (SICI) during varying levels of muscle activation.
Main Methods:
- Transcranial magnetic stimulation (TMS) was applied to 30 healthy participants using a circular coil.
- Motor-evoked potentials (MEPs) were recorded from the abductor pollicis brevis muscle at rest and during voluntary contraction (facilitation).
- Short-interval intracortical inhibition (SICI) was measured at rest and during facilitation.
Main Results:
- Facilitation significantly prolonged MEP duration, with increases correlating with TMS stimulus intensity.
- MEP amplitude also increased with facilitation and stimulus intensity, but exhibited a ceiling effect.
- A significant inverse relationship was observed between SICI and MEP duration, both at rest and during facilitation.
Conclusions:
- Changes in MEP duration and amplitude during voluntary contraction appear to be mediated by similar physiological processes.
- Both cortical and nonpropriospinal spinal mechanisms likely contribute to the observed changes in MEP duration.
- The strong correlation between MEP duration and SICI suggests a significant role for cortical mechanisms in modulating MEP duration during muscle activation.
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