Neurobehavioral aspects of cerebral white matter disorders.

The study of higher function in humans requires a consideration of all the neural tissues in the brain. Long neglected as a contributor to the organization of cognitive and emotional operations, the cerebral white matter is now the subject of substantial effort to improve understanding. Among the many approaches that can address this area usefully, the study of individuals with white matter disorders offers a wealth of clinical insights that exploits the time-tested lesion method of behavioral neurology. This process is complemented by sophisticated neuroimaging techniques that increasingly enable detailed visualization of white matter tracts as they participate in the cognitive and emotional operations of distributed neural networks. In practical terms, an appreciation of the neurobehavioral importance of white matter disorders can be of great benefit for patients seen by neurologists and psychiatrists alike, especially because early recognition and treatment often can have an important influence on outcome. In theoretical terms, a focus on the white matter and its disorders promises to expand knowledge of the brain as an extraordinarily complex organ in which the connectivity provided by white matter is central to cognition, emotion, and consciousness itself. As the details of white matter structure and function become clarified, a more complete portrait of the organ of the mind can be anticipated.