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Human consciousness comprises three major dimensions, arousal, emotion and cognition. Leaving emotion aside for the purposes of this review, coma represents a complete loss of arousal function, whereas the vegetative state describes a total absence of aroused cognition. Less severe impairments abound, with hypersomnia or apathetic inattention appearing as moderate to intense impairments on the scale of arousal and either global dementias or partial, selective psychological reductions such as amnesia or aphasia falling along the psychological axis. Among the latter partial deficits, transient global amnesia (TGA), the role of the thalamus in cognition, and the biology of the vegetative state have drawn the particular interest of neurologists in the recent past.