The Executive Motor System works Harder when Moving the Non-Preferred Hand

Purpose: The aim of the present study was to investigate whether human hand preference has a functional correlate in movement-related neuronal activity. Methods: 12 right-handed and 13 left-handed volunteers performed visually cued choice reaction time tasks during event-related 3 Tesla fMRI. The experimental design comprised five conditions, differing in the amount of choice given by spatial cues. Responses were made with the left or right index or middle finger. Subjects were required to choose and execute brisk flexion movements with only one finger in response to the spatial cue. Data were analyzed with SPM2. Results: Using the left hand, right-handed subjects showed significantly (p<0.05, corrected) greater movement-related BOLD increase in the corresponding executive motor areas (right sensory motor cortex, right insula, right putamen, left cerebellum) relative to left-handed participants. Vice versa, using the right hand, the corresponding executive motor system showed greater neuronal activity in left-handed compared with right-handed subjects. This pattern of neuronal activity was similar across all experimental conditions, indicating that the effect was independent of motor selection based on spatial cues. Discussion: Movement-related activity levels in corresponding executive motor areas are higher if motor responses are made with the non-preferred (less trained) hand. We attribute the relative increase in BOLD signal to the additional effort that is required when moving the less skilled hand. Interestingly, this pattern equally applies for both left- and right-handers.