Activation of Sensorimotor Cortex and Supplementary Motor Area during Bimanual Movement: Analysis Using Functional Magnetic Resonance Imaging.

Abstract

Functional magnetic resonance imaging (fMRI) provides a method for ana-lyzing physiological roles of the sensorimotor cortex (SMC) and supplementary motor area (SMA) during voluntary movement. Although there are many reports on this theme, bimanual movement has rarely been studied. We investigated the activation of SMC and SMA during bimanual agonistic and antagonistic hand motions. Fourteen right-handed normal volunteers (mean age, 24.9yr) performed three kinds of motor tasks which required the repetitive making and opening of a fist: unilateral movement of the left hand (task A), simultaneous agonistic movement of both hands (task B, repeatedly making fists of both hands simultaneously then opening them simultaneously), simultaneous antagonis-tic movements of both hands (task C, making a fist and simultaneously opening the contralateral fist, and the reverse). Each task consisted of multiple periods of 20 sec of rest (resting period) alternating with periods of 20sec motor execution (activation period). A task consisted of eight repetitions of this rest-activation cycle. Three slices of axial fMRI were obtained by the gradient-echo and echo-planar (1.5T) methods using the following parameters: echo time (TE)=50ms, repetition time (RT)=1,000ms, slice thickness=7 mm, field of view (FOV)=220X220mm, matrix=91X128, flip angle=750. Totally, 255 functional images (85 images per slice) were obtained for each task. Cross-correlation with the time domain was used to detect significantly activated pixels. SMA was activated most in task C. There was no marked difference between task A and task B, evidence of the significant role of SMA in motor control during antagonistic hand movement (task C). Activation at the ipsilateral SMC during left hand motion (task A) occurred in only 3 of the 14 subjects. A comparison of SMC activities showed that the least activation occurred during task B. SMC activity is reported to be affected by the complexity of unilateral hand movement. Our findings support this in terms of bimanual motion and suggest that bimanual agonistic movement (at least in the making and opening of a fist) is simpler and more automatic than either bimanual antagonistic movement or unilateral hand movement.