Strength as a factor influencing mirror movements

A finger flexion task was used to investigate intensity of mirror movement. Subjects were asked to maintain target forces, with either their index or small finger, that represented 25, 50 or 75 percent of their maximum strength capacity for the finger performing the task. Relative to the force produced, males and females exhibited the same amount of mirror movement. However, mirror movement relative to force exerted was greater when the left hand performed the task, a finding consistent with previous research. Greater amounts of mirror movement were recorded for movements of the small finger compared to the index finger, consistent with the cortical activation explanation (Todor and Lazarus, 1986). These results suggest that strength differences are not the principal determinant of intensity of mirror movement. Rather, differing functional roles of the hands and fingers, reflecting differences in cortical activation and organisation, appear to mediate the intensity of mirror movement occurrence.