A functional MRI investigation of bilateral cortical activation during unilateral voluntary motor activity and electromyostimulation

It is known that chronic unilateral motor activity or electromyostimulation (EMS) may result in bilateral adaptation, a phenomenon termed cross education. One of the hypotheses for the potential mechanisms of cross education is an adaptation caused by bilateral cortical coactivation during unilateral voluntary exercise. Whether EMS induced cross education involves bilateral cortical activation is unknown. This study aimed to examine cortical activities by functional MRI (fMRI) during unilateral voluntary and EMS evoked muscle contractions. Six healthy young men performed two tasks. One was three sets of 10 maximum isometric dorsiflexions of the right ankle, each set for 1-min followed by 1-min rest; and the other was three sets of 1-min EMS on tibialis anterior muscle at a duty cycle of 3-s on 3-s off, each followed by 1-min rest. During the tasks brain fMRI images were obtained using a 1.5T GE MRI scanner, and analysed using SPM99 software. Results demonstrated bilateral activation of the primary motor area, secondary somatosensory area and cingulated gyrus area during both tasks. Furthermore, the voluntary contraction increased fMRI signals in supplementary motor area, premotor cortex and cerebellum bilaterally, and primary somatosensory area of the contralateral side; while EMS increased bilateral activity in primary somatosensory area and ipsilateral premotor cortex and contralateral supplementary motor area. It was evident that the voluntary and EMS tasks activated certain common areas as well as specific areas in the brain, indicating cortical mechanisms may be involved in both voluntary exercise and EMS induced cross education.