Motor demand dependent activation of ipsilateral motor cortex 1

28 29 The role of ipsilateral primary motor cortex (M1) in hand motor control during complex 30 task performance remains controversial. Bilateral M1 activation is inconsistently 31 observed in fMRI studies of unilateral hand performance. Two factors limit the 32 interpretation of these data. As the motor tasks differ qualitatively in these studies, it is 33 conceivable that M1 contributions differ with the demand on skillfulness. Second, most 34 studies lack the verification of a strictly unilateral execution of the motor task during the 35 acquisition of imaging data. Here, we use fMRI to determine whether ipsilateral M1 36 activity depends on the demand for precision in a pointing task where precision varied 37 quantitatively while movement trajectories remained equal. Thirteen healthy participants 38 used an MRI-compatible joystick to point to targets of 4 different sizes in a block design. 39 A clustered acquisition technique allowed simultaneous fMRI/EMG data collection and 40 confirmed that movements were strictly unilateral. Accuracy of performance increased 41 with target size. Overall, the pointing task revealed activation in contralateral and 42 ipsilateral M1, extending into contralateral somatosensory and parietal areas. Target size 43 dependent activation differences were found in ipsilateral M1 extending into the 44 temporal/parietal junction, where activation increased with increasing demand on 45 accuracy. The results suggest that ipsilateral M1 is active during the execution of a 46 unilateral motor task and that its activity is modulated by the demand on precision. 47 48