'Direct' and 'crossed' modulation of human motor cortex excitability following exercise

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Repetitive movements can alter motor cortex excitability.
• The role of sensory feedback in this modulation is not fully understood.
• Crossed effects in motor cortex excitability are increasingly recognized.

Purpose of the Study:

• To investigate the role of peripheral sensory feedback in motor cortex excitability changes.
• To examine the effects of exercise on the non-activated primary motor cortex (MI).
• To explore potential interhemispheric mechanisms underlying crossed effects.

Main Methods:

• Transcranial magnetic stimulation (TMS) was used to assess primary motor cortex (MI) excitability.
• Motor evoked potential (MEP) amplitudes were measured before and after interventions.
• Peripheral sensory stimulation (vibration, electrical nerve stimulation) and thumb exercise were employed.

Main Results:

• Thumb exercise significantly decreased MEP amplitude in non-exercised homologous muscles (P < 0.01).
• Peripheral sensory stimulation did not alter MEP amplitude, indicating no role in MI excitability modulation.
• Exercise led to a contraction of motor cortical output maps in the non-activated hemisphere.

Conclusions:

• Peripheral sensory feedback is not the primary mechanism for exercise-induced MI excitability changes.
• Exercise can induce homologous changes in the non-activated motor cortex, suggesting a 'crossed' effect.
• Interhemispheric transfer of information via the corpus callosum may mediate these crossed effects in motor cortex excitability.