Crossed apraxia: Implications for handedness

Liepmann posited that right hand preference relates to left hemisphere domi nance for learned skilled movements. Limb apraxia, impairment of skilled mo vement, typically occurs in individuals with left hemisphere (LH) lesions. The occurrence of apraxia in right-handed individuals following right-hemis phere lesions appears to refute Liepmann's hypothesis. We studied the aprax ia of a right-handed man, RF, following a right frontal lesion to determine whether his apraxia paralleled the apraxia seen following LH lesions. Resu lts of behavioral testing indicated that, like individuals with apraxia fol lowing left frontal lesions, RF was better at gesture recognition than gest ure production which was significantly impaired across tasks. Kinematic mot ion analyses of movement linearity, planarity, and the coupling of temporos patial aspects of movements substantiated the parallel impairments in RF an d patients with LH apraxia. The impairment seen in our patient with crossed apraxia provides evidence for the fractionation of systems underlying hand preference and skilled movement.