Isolated acalculia due to left parietal lesion.
To clarify the characteristics and the localization of isolated calculation disturbances due to left parietal lesions. Case series. Tertiary care hospital. Three referred patients with isolated calculation disturbances due to stroke in the left parietal region. Sixteen volunteers for age and education constituted the control group. Neuropsychological tests, including a battery of tests for acalculia and the Wechsler Adult Intelligence Scale, and magnetic resonance imaging were performed. Three patients made calculation errors in the process where a number of steps were carried out simultaneously. The patients showed no aphasic components in number operations. They understood the basic processes of calculation. They showed little difficulty in the retrieval of table values. The patients had no impairment in aligning arithmetic problems or in assigning and maintaining place-holding values. They did not show any deficit of immediate memory for calculation problems. Overlapping lesions were located along the left intraparietal sulcus. The area lying along the left intraparietal sulcus is critical for isolated parietal acalculia. The profile of isolated acalculia suggests that it results from the disruption of the working memory for calculation.