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Ipsilateral contraction increases map area and decreases motor threshold for contralateral hand muscle
Mustaali Hussain1, Stevie D Foglia2, Jiyeon Park1
1Department of Kinesiology, McMaster University, 1280, Main Street West Hamilton, Ontario L8S 4L8, Canada.
Neuroscience
|September 25, 2025
Summary
Ipsilateral hand contractions enhance motor cortex excitability and representation size in the primary motor cortex (M1). These effects on motor control are consistent across different handedness and biological sexes.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Ipsilateral motor pathways from the primary motor cortex (M1) to the upper limb are known in humans.
- These pathways can influence corticomotor excitability of contralateral homologous muscles.
- The impact of handedness and biological sex on ipsilateral motor representations is not well understood.
Purpose of the Study:
- To investigate how ipsilateral hand contraction affects motor representation size and excitability in M1.
- To determine if these effects are influenced by handedness or biological sex.
Main Methods:
- Transcranial magnetic stimulation (TMS) was used in 80 participants (40 right-handed, 40 left-handed, equal males and females).
- Motor threshold and motor map area of the first dorsal interosseus (FDI) muscle were measured.
- Measurements were taken at rest and during low-level (10% MVC) ipsilateral FDI contraction.
Main Results:
- Ipsilateral hand contraction led to an increase in motor map area within M1.
- Ipsilateral contraction also resulted in a decrease in motor threshold.
- These observed changes were consistent regardless of handedness or biological sex and were similar across both hemispheres.
Conclusions:
- Ipsilateral hand contractions enhance the size and excitability of motor representations in the ipsilateral M1.
- These neurophysiological changes are independent of individual handedness and biological sex.
- This suggests a robust mechanism for modulating motor cortical excitability via ipsilateral input.
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