Mirror movement asymmetries in congenital hemiparesis: the inhibition hypothesis revisited.

Mirror movements are seen in normal children in the first decade. The movements persist after age 10 in patients with congenital hemiparesis. At first, mirror movements are more prominent in the good hand (when the impaired hand attempts a unimanual task), but after age 10, mirroring diminishes in the good hand, and these movements are equally prominent in good and impaired hands. Maturational changes in callosally mediated inhibition of uncrossed motor pathways and reorganizational changes of the pyramidal motor system after early unilateral brain injury explain these age-dependent changes in asymmetries of mirror movements.