The Effect of Handedness on Supplementary Motor Area Activation during Complex Motor Tasks

Functional magnetic resonance imaging (fMRI) was used to assess the activity of supplementary motor area (SMA) in six right-handed and six left-handed healthy volunteers. Two manual tasks (self-initiated previously practiced and unpredictable visually guided) were used. Quantitative analysis of hemispheric and bilateral SMA activation was described as mean ± standard deviation of hot spots/total spots. The two tasks induced bilateral SMA activation. The laterality of SMA activation was affected by manual dominance. Left SMA was significantly more activated in right- and left-handers while performing the motor tasks with the right hand. Right SMA was more activated in the left-handers when the left hand was used. Task complexity was the most important factor influencing the degree of SMA activation.