Background
In the brain, the dominant primary motor cortex (M1) has a greater hand representation area, shows more profusehorizontal connections, and shows a greater reduction in intracortical inhibition after hand exercise than does the non-dominant M1,suggesting a hemispheric asymmetry in M1 plasticity. Methods: We performed a transcranial magnetic stimulation (TMS) study toinvestigate the hemispheric asymmetry of paired associative stimulation (PAS)-induced M1 plasticity in 9 right-handed volunteers.Motor evoked potentials (MEPs) were measured in the abductor pollicis brevis (APB) muscles of both hands, and MEP recruitmentcurves were measured at different stimulation intensities, before and after PAS. Results: MEP recruitment curves were significantlyenhanced in the dominant, but not the non-dominant M1. Conclusions: These results demonstrate that the dominant M1 has greaterPAS-induced plasticity than does the non-dominant M1. This provides neurophysiological evidence for the asymmetricalperformance of motor tasks related to handedness.
