Changes in cortical excitability during and just before motor imagery.

OBJECTIVE Changes in cortical excitability during motor imagery were investigated in order to reveal the effect of hand dominance. During motor imagery, motor evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) muscle of the dominant hand using transcranial magnetic stimulation (TMS). METHODS Twelve healthy right-handed subjects participated. Three motor imagery tasks (MITs) were provided; dominant hand grasping, non-dominant hand grasping, and ankle dorsiflexion ipsilateral to the dominant hand. MEPs were also recorded from the FDI muscle of the non-dominant hand during the same tasks. RESULT MEPs increased significantly in the dominant hand during MIT, just before MIT of the dominant hand, and prior to ankle dorsiflexion ipsilateral to the dominant hand. MEPs obtained from the FDI muscle of the dominant hand during MITs were greater than that obtained from the FDI muscle of the non-dominant hand. However, this difference was not significant. CONCLUSION The left primary motor cortex (M1) was more excited than M1 during MITs of the hand muscles. Cortical excitability increased just before MIT of the contralateral hand and leg muscles.