Written language production disorders: historical and recent perspectives.

Written language production is often the least examined neuropsychological function, yet it provides a sensitive and subtle sign to a variety of different behavioral disorders. The dissociation between written and spoken language and reading and writing first came to clinical prominence in the nineteenth century, with respect to ideas about localization of function. Twentieth century aphasiology research focused primarily on patients with unifocal lesions from cerebrovascular accidents, which have provided insight into the various levels of processing involved in the cognitively complex task of producing written language. Recent investigations have provided a broader perspective on writing impairments in a variety of disorders, including progressive and diffuse brain disorders, and functional brain imaging techniques have been used to study the underlying processes in healthy individuals.