Figure 3.

Prefrontal and posterior parietal areas engaged during the hand-selection phase in the bimanual trials. A, Clusters with a main effect of grip type (bimanual, unimanual) superimposed on the MNI “glass brain.” Purple and yellow areas indicate clusters located in prefrontal and posterior parietal cortical areas, respectively, and areas outlined in red depict mark cluster in the SMC regions. Histograms show, for each grip type (BiM, bimanual; UniM, unimanual) and mapping rule (L, left-hand; R, right-hand), the BOLD effect sizes (β values) in percentage relative to mean BOLD signal level during the session. Height of columns gives mean value across participants, and vertical lines represent 1 SE (n = 16). B, Left column shows the time course of the BOLD signal averaged across all voxels in the clusters labeled by a, b, and c in A for data obtained in the bimanual and unimanual trials, respectively. The signal change is given in percentage relative to mean of session, and the curves are aligned to zero at the onset of the target-chasing task. The thin gray curve shows the time course of the hemodynamic response function corresponding to the regressor representing the hand-selection phase averaged across participants and arbitrarily scaled. Right column shows the corresponding BOLD data after the variation in the BOLD signal explained by the other regressors in the model was factored out, thus providing a view of what the regressor representing the hand-selection phase can capture. The embossed segment of the abscissa indicates the period of the target-chasing task. Black dots indicate interscan intervals. C, D, Main effect of grip type within the prefrontal cortex (purple) and posterior parietal cortex (yellow) shown on coronal and transversal slices of the averaged brain calculated across the participant-specific T1-weighted images (n = 16) after being normalized to the MNI brain template. SPL, Superior parietal lobule; IPS, intraparietal sulcus; R, right; L, left; A, anterior; P, posterior.