24-h polysomnographic recordings and electrophysiological spectral analyses from a cohort of patients with chronic disorders of consciousness.

Fourteen patients with severe brain injuries and chronic disorders of consciousness underwent polysomnographic recordings for a 24-h period. Their electrophysiological data were scored using a modified sleep staging system employed in a previous study of similar patients (J Head Trauma Rehabil 30:334-346, 2015). In addition to sleep scoring, the patients' data were compared with a sample of approximately age-matched healthy volunteers in the spectral domain. All patients demonstrated some form of a sleep-wake cycle; however, the integrity of normal sleep features was remarkably heterogenous across individuals, and in some cases, sleep was significantly impoverished. In three patients, these cycles were biphasic and comprised of only alternating periods of wakefulness and sleep-like electrophysiological activity. Two patients demonstrated a sleep-wake cycle that included all sleep stages aside from non-REM stage 3, and another two patients demonstrated a sleep-wake cycle that included all sleep stages aside from REM sleep. The remaining seven patients, which included patients diagnosed as being in a minimally conscious state and patients diagnosed as being in a vegetative state (unresponsive wakefulness syndrome), demonstrated full sleep architecture, including k-complexes, REMs, and slow wave sleep. However, three of the patients with full sleep architecture did not generate sleep spindles. Altogether, these findings highlight the heterogeneity of brain function among patients with disorders of consciousness, regardless of their diagnostic category. Polysomnography is a useful tool to complement other behavioural and physiological assessments that characterize the abilities of each patient.