Dominance of the right hemisphere for visually guided actions

The aim of this project was to investigate whether there is hemispheric dominance for visually guided finger movements independent of the side of the effector.

Methods: We studied 12 right-handed healthy subjects while they performed a visuo-spatially cued choice reaction time task. BOLD-signal changes in relation to movements with the right or left index or middle finger were measured with event-related fMRI. Contrast images (CI) were calculated for responses with the right or left hand respectively. CI representing right handed responses where flipped along the x-axis in MNI-space. In the resulting images, activation clusters, that originally were in the right hemisphere, now are located in the left hemisphere and vice versa. Individual CI of all participants were compared in a multivariate design to characterize effector-independent differences in activation between hemispheres (SPM2, www.fil.ion.ucl.ac.uk/spm; p<0.05, corrected).

Results: In right-handers, an area located at the parieto-occipital junction (POJ) of the right hemisphere was more active than its counterpart in the left hemisphere, independent of the responding hand.

Discussion: POJ forms an area of the dorsal visual stream. Visual information reaches the superior parietal lobule via POJ, and POJ has strong direct connections to the dorsal premotor cortex. This is the first study to show a functional dominance of the right hemisphere for visually guided finger movements. This finding corroborates the right-hemispheric dominance for spatial processing.