Disconnection Syndromes

Abstract

Disconnection syndromes were classical behavioral neurology disorders explained, not be localized neocortical lesions, but by disconnection of pathways between critical cortical areas. Disconnection theory was a historically important explanation for traditional behavioral neurology and foundational to the field. It was originally conceived as unidirectional and non-interactive interruptions between primary sensory areas and motor, limbic, or language areas. Disconnection between these areas did not occur directly, but, rather through their association cortices. There were specific neocortical areas, however, where cross-modal associations could occur; these “association areas of association areas” most notably including the left inferior parietal lobule. Developments in tractography and functional magnetic resonance imaging have replaced the original simplistic pathways with extensive structural white matter tracts and functional resting state neural networks. These imaging techniques, and their mathematical analyses, have infused new life into the concept of disconnection of pathways as an explanation for brain disorders, and has expanded disconnection theory to include network interactions, hyperconnectivity, and misconnections. As the brain can be envisaged as interacting networks with levels of optimal connectivity, modern views of disconnection theory may prove valuable in understanding both the organization of behavior in the brain and the underlying disturbances in neuropsychiatric disorders.