Sleep in disorders of consciousness

Abstract

From a behavioral as well as neurobiological point of view, sleep and consciousness are intimately connected. A better understanding of sleep cycles and sleep architecture of patients suffering from disorders of consciousness might therefore improve the clinical care for these patients as well as our understanding of the neural correlates of consciousness. Defining sleep in severely brain-injured patients is however problematic as both their electrophysiological and sleep patterns differ in many ways from healthy individuals. This work discusses the concepts used when studying sleep in patients suffering from disorders of consciousness and critically assesses the applicability of standard sleep criteria in these patients. The available literature on comatose and vegetative (unresponsive wakefulness) states as well as that on locked-in and related states following traumatic or non-traumatic severe brain injury will be reviewed. A wide spectrum of sleep disturbances ranging from almost normal patterns to severe loss and architecture disorganization are reported with some sleep patterns being correlated to diagnosis or prognosis. At present the interactions of sleep and consciousness in brain-injured patients are little studied, yet highly interesting subject, which should receive more attention in the future.