Ipsilateral brain deactivation specific to the nondominant hand during simple finger movements.

Sequential finger movements of the unilateral hand and associated brain activities have been extensively investigated. The current functional magnetic resonance imaging (fMRI) study was designed to explore the differential patterns of brain activation and deactivation between dominant and nondominant hands, using independent-component analysis (ICA). Eight right-handed and two left-handed participants, all native Chinese, were included in this study. fMRI data were acquired for each participant while performing dominant and nondominant hand movements sequentially, using a box-car design. ICA was applied to the sequentially realigned, spatially normalized, and smoothed fMRI data. Consistent with earlier findings, we found that the contralateral primary motor and premotor cortices, as well as the bilateral supplementary motor areas, were all activated for both dominant and nondominant hand-movement tasks. More interestingly, the ipsilateral primary motor cortex was deactivated only for the nondominant hand, and no ipsilateral deactivation was detected for the dominant hand. This dominant/nondominant deactivation difference was consistent for all participants, regardless of their handedness. These results suggest asymmetrically functional patterns for the dominant and nondominant motor cortices.