Arcuate fasciculus variability and repetition: the left sometimes can be right.

Repetition ability is a major criterion for classifying aphasic syndromes and its status is helpful in the determination of the involved neural structures. It is widely assumed that repetition deficits correlate with injury to the left perisylvian core including the arcuate fasciculus (AF). However, descriptions of normal repetition despite damage to the AF or impaired repetition without AF involvement cast doubts on its role in repetition. To explain these paradoxes, we analyse two different aphasic syndromes - in which repetition is selectively impaired (conduction aphasia) or spared (transcortical aphasias) - in light of recent neuroimaging findings. We suggest that the AF and other white matter bundles are the anatomical signatures of language repetition and that individual variability in their anatomy and lateralisation may explain negative cases.