The role of arousal and "gating" systems in the neurology of impaired consciousness

A brief taxonomy of neurologic disorders resulting in global impairments of consciousness is presented. Particular emphasis is placed on focal injurie s of subcortical structures that may produce disorders that are otherwise a ssociated to large bilateral cortical injuries. A distinction between subco rtical arousal and "gating" systems is developed. Both clinical and experim ental studies are reviewed in the context of these disorders and their poss ible underlying mechanisms.