Interhemispheric plasticity in humans

Area of Science:

• Neuroscience
• Motor Control
• Neuroplasticity

Background:

• Unimanual motor practice enhances motor output in both trained and untrained homologous muscles.
• This phenomenon, known as interlimb cross-education, suggests neural adaptations in the non-trained limb's motor cortex.
• The study investigates the role of motor cortical excitability and interhemispheric inhibition in mediating cross-education.

Purpose of the Study:

• To examine the hypothesis that adaptations in motor cortical excitability and interhemispheric inhibition underlie interlimb cross-education.
• To determine the relationship between changes in corticospinal excitability and interhemispheric inhibition with the degree of cross-education.

Main Methods:

• Healthy volunteers (n=12) performed 1000 submaximal voluntary contractions of the right first dorsal interosseus (FDI) over 20 sessions.
• Transcranial magnetic stimulation (TMS) measured corticospinal excitability and intracortical inhibition/facilitation in the non-trained primary motor cortex (iM1).
• Interhemispheric inhibition was assessed between the trained and non-trained motor cortices.

Main Results:

• Trained FDI MVC increased by 49.9%, and untrained FDI MVC increased by 28.1%.
• Chronic reductions in interhemispheric inhibition (30.9%) were strongly associated with cross-education.
• While resting motor cortex excitability showed a modest increase, it did not correlate with cross-education.

Conclusions:

• Findings provide the first evidence that plasticity of interhemispheric connections mediates cross-education from a simple motor task.
• Reduced interhemispheric inhibition is a key neural mechanism underlying interlimb motor learning and skill transfer.