Lateralization of motor circuits and handedness during finger movements.

Although functional lateralization in the human brain has been studied intensively, there remains significant controversy over the brain mechanisms that instantiate it. The main objective of the present study is to characterize the regions associated with the generation of different movements by the fingers of both hands by right- and left-handed people. Thirteen right- and left-handers were studied using blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) during performance of single and sequential finger movement tasks. We used single-shot whole-brain spiral fMRI to map the functional components of the motor system during these tasks. Regions of interest included the primary motor and sensory cortices, the pre-motor cortices and the cerebellum. Sequential movements were associated with intense brain activation in several bilateral regions, whereas single movements were associated with less activation in fewer regions, but with greater laterality. Right- and left-handers differed in their pattern of activation, sharing a pattern of activation on simple movements but responding differently to sequential movements. On simple movements, the brain activation patterns of left- and right-handers were similar in volume, number of areas and laterality. By contrast, on sequential movement, left-handers activated larger volumes and a larger number of brain areas than right-handers, and showed significantly less brain lateralization. These results highlight differences in the functional organization of motor areas in right- and left-handed people. The discrepancies that might reflect differences in the network features of motor systems in these two groups, could also determine differences in motor activity that occur during recovery from injury (e.g. after stroke).