Mirror movements in normal adult subjects.

Intensity of mirror movements occurring under specific task conditions in normal adults was investigated using a finger flexion task. Subjects were asked to sustain target pressures using different fingers. Greater pressures of mirror movement were recorded when the weaker, small finger of either hand performed the task. The target pressure which subjects were asked to sustain did not influence the amount of mirror movement exhibited by either males or females, even though higher target forces required a significantly greater percentage of total finger strength. On average, males exhibited the same quantity of mirror movements as female subjects, despite the force requirements of the task representing for them a significantly smaller percentage of total finger strength. Moreover, when the right hand performed the experimental tasks, less mirror movement was exhibited than when the left hand was active. Thus, the left hand showed stronger mirror movements. The findings were consistent with previous research using children as subjects, although the nonsignificant effects of gender and pressure were unexpected and need to be examined further. It appears that, while the force requirement of the task does influence the magnitude of mirror movement, it is not the principle determinant.