The impact of learning on brain functional laterality has not been systematically investigated. We em- ployed an event-related functional magnetic resonance im- aging combined with a delayed sequential movement task to investigate brain activation pattern and laterality during a transient practice in 12 subjects. Both hemispheres, involving motor areas and posterior parietal cortex, were engaged during motor preparation and execution, with larger activa- tion volume in the left hemisphere than in the right. Activa- tion volume in these regions significantly decreased after a transient practice, with more reduction in the right hemi- sphere resulting increase in left lateralization. The theoretical implications of these findings are discussed in relation to the physiological significance of brain functional laterality.
Whether the secondary motor areas are involved in simple voluntary movements remains controversial. Differences in the neural substrates of movements with the dominant and the non-dominant hands have not been well documented. In the present study, functional magnetic resonance imaging (fMRI) was used to investigate the hemodynamic response in the primary motor cortex (M1), supplementary motor area (SMA) and premotor cortex (PMC) in six healthy right-handed subjects while performing a visually-guided finger-tapping task with their dominant or non-dominant hands. Significant activation was observed in M1, SMA and PMC during this externally triggered simple voluntary movement task. While dominant hand movements only activated contralateral motor areas, non-domi- nant hand movements also activated ipsilateral SMA and PMC. The results provide strong evidence for the involvement of the secondary motor areas in simple voluntary movements, and also suggest that movements of the dominant hand primarily engage the contralateral secondary motor areas, whereas movements of the non-dominant hand engage bilateral secondary motor areas.
