Sleep in disorders of consciousness: diagnostic, prognostic, and therapeutic considerations

Purpose of review Sleep is important in the evaluation of patients with disorders of consciousness (DOC). However, it remains unclear whether reconstitution of sleep could enable consciousness or vice versa. Here we synthesize recent evidence on natural recovery of sleep in DOC, and sleep-promoting therapeutic interventions for recovery of consciousness. Recent findings In subacute DOC, physiological sleep--wake cycles and complex sleep patterns are related to better outcomes. Moreover, structured rapid-eye-movement (REM), non-REM (NREM) stages, and presence of sleep spindles correlate with full or partial recovery. In chronic DOC, sleep organization may reflect both integrity of consciousness-supporting brain networks and engagement of those networks during wakefulness. Therapeutic strategies have integrated improvement of sleep and sleep--wake cycles in DOC patients; use of bright light stimulation or drugs enhancing sleep and/or vigilance, treatment of sleep apneas, and neuromodulatory stimulations are promising tools to promote healthy sleep architecture and wakeful recovery. Summary Sleep features and sleep--wake cycles are important prognostic markers in subacute DOC and can provide insight into covert recovery in chronic DOC. Although large-scale studies are needed, preliminary studies in limited patients suggest that therapeutic options restoring sleep and/or sleep--wake cycles may improve cognitive function and outcomes in DOC.