Callosal apraxia.

A 39-year-old right-handed woman suffered a ruptured pericallosal aneurysm. Serial MRI studies showed damage to the genu and most of the body of the corpus callosum but not the splenium. Both supplementary motor areas (SMA) appeared intact. We studied the patient's praxis performance at intervals over a 4-month period with a standardized battery. The study suggests that apraxia seen in patients with callosal lesions is probably due to the callosal damage, not to the usually associated SMA lesion. Our findings support Liepmann's idea that the left hemisphere is dominant for praxis in both hands. We propose, however, that the dominance effect is related to the type of test given and varies among individuals. As regards the latter, in some individuals the left hemisphere is strongly dominant for motor tasks, while in others it is less so. As regards the type of test, the most enduring left-hand apraxia is seen in verbal, not visuomotor tests.