Praxis and writing in a right-hander with crossed aphasia.

Studies of patients with brain lesions have demonstrated that language and praxis are mediated by dissociable networks. However, language has the capacity to influence the selection of purposeful actions. The abilities to use language and to program purposeful movements are often mediated by networks that have anatomic proximity. With hemispheric injury, the diagnosis of apraxia is often confounded by the specific influence of language impairments on the ability to select and produce transitive gestures. We report a patient who illustrates this confound. This patient is a right-handed man who developed global aphasia and neglect after a right hemispheric stroke. His right hand remained deft, and when asked to produce specific transitive gestures (pantomimes), he often performed normally but did make some body part as object and perseverative errors. However, he did not demonstrate the temporal or spatial errors typical of ideomotor apraxia. He also had a perseverative agraphia. Our patient's left hemisphere praxis system appeared to be intact, and the error types demonstrated during production of transitive gestures cannot be attributed to a degradation of postural and movement (praxis) programs mediated by his left hemisphere. The praxis errors types are most consistent with a deficit in the ability to select the necessary praxis programs. Thus, our patient appeared to have dissociation between language and praxis programs that resulted in body part as object and perseverative errors.