Disorders in executive control functions among aphasic and other brain-damaged patients.

Four experimental procedures for assessing disorders of executive control (Nonverbal Continuous Performance, Graphic Pattern Generation, Sequence Generation Test, and Tower of Hanoi) were administered to 22 left-brain-damaged aphasic patients, 19 right-brain-damaged nonaphasic patients, and 49 healthy controls. Aphasic patients with frontal-lobe lesions were significantly more impaired on these tasks than aphasics with retrorolandic or mixed lesions in the left hemisphere. Patients with right-hemisphere lesions, especially those with frontal-lobe lesions, showed even greater impairments on these visual/spatial tasks. The results suggest that aphasics' impairments in executive control are independent of their linguistic and visuospatial deficits and are specific to lesions in left frontal and prefrontal regions. The clinical utility of the experimental procedures is discussed.