Praxis performance with left versus right hemisphere lesions

Praxis is defined as skilled, purposive limb movement. While it has been a consistent finding that lesions of the left cerebral hemisphere result in significantly worse performance on praxis testing than lesions of the right cerebral hemisphere, recently some investigators have proposed that the right hemisphere may also play an important role in mediating praxis. To learn if the right hemisphere does have a role in praxis we studied right-handed patients with right or left hemisphere lesions, as well as right-handed normal controls who were matched for age and education. Two trained raters scored the transitive gesture performance of the forelimb ipsilateral to the injured hemisphere. For the normal controls, left and right hand performances were scored separately and used for statistical comparison. Independent comparisons were made on six dimensions that are important for accurate gesture performance and on an overall apraxia score. When compared to normal control subjects the patients with left hemisphere lesions (LHD) did demonstrate deficient praxis; that is, ideomotor apraxia. However, those with right hemisphere lesions (RHD) did not. Based on this study it would appear that the right hemisphere does not play a crucial role in praxis.