Disorders of consciousness: anatomical and physiological mechanisms

The anatomical and physiological mechanisms of consciousness are reviewed, focussing on the wakefulness mechanisms, which are one aspect, albeit an indispensable one, of consciousness. In trying to understand disorders of consciousness, it must be remembered that wake physiology is linked to sleep physiology and a brief summary of the phenomenology and regulation of the wake sleep cycle is therefore presented. Wakefulness is produced and maintained by a complex neural network composed of at least ten groups of neurones, which spread out from the medulla oblongata to the telencephalic structures. Some of these elements (reticular formation and diffuse thalamic nuclei) contribute to the arousal and general activation of the brain, while others (aminergic and peptidergic neurones) contribute to the quality of wakefulness, as well as to general activation. Disorders of wakefulness may be due to dysfunction of one or several elements of the wake network or sleep disorders, as well as to sleep deprivation.