Isolation of a right hemisphere cognitive system in a patient with anarchic (alien) hand sign.

We report evidence of isolated conceptual knowledge in the right hemisphere of a woman with chronic anarchic hand sign after ischemic infarction of the central four-fifths of the corpus callosum. Limited visual information was available to the right hemisphere, access to medial temporal structures subserving memory was disrupted and disconnection from left hemisphere language structures was complete. Still, the right hemisphere could build mental representations of objects via tactile input and use them in cross-modal matching. These representations were not accessed consistently in auditory comprehension or naming tasks. This functional specificity and its pathoanatomical correlates demonstrate that the study of anarchic hand sign can illuminate not just motor control issues but may inform our understanding of the representation and lateralization of conceptual knowledge as well.