From Dawn to Dusk – Mimicking Natural Daylight Exposure Improves Circadian Rhythm Entrainment in Patients with Severe Brain Injury

Background:Better integrity of circadian rhythms has been shown to relate to a richer behavioral repertoire in patients with disorders of consciousness (DOC). As light exposure has proven successful in treating circadian rhythm disorders, we sought to investigate whether simulating natural daylight in a clinical setting can entrain circadian rhythms in patients with DOC, and thus lead to an improvement of their clinical state as assessed with the Coma Recovery Scale-Revised (CRS-R).Methods:We recorded skin temperature continuously over 7–8 consecutive days in patients with DOC (i.e. unresponsive wakefulness syndrome [UWS; n=15] and minimally conscious state [MCS; n=2]) in each of two conditions: (1) habitual light (HL), and (2) dynamic daylight (DDL) condition. While patients were in a room with usual clinic lighting in the HL condition, they were in an otherwise comparable room with biodynamic lighting (i.e. higher illuminance and dynamic changes in spectral characteristics during the day) in the DDL condition.Results:Behaviorally, patients scored higher on the CRS-R (sum scores) in the DDL compared to the HL condition. Physiologically, the period length of the patients’ circadian temperature rhythms was closer to 24h in the DDL condition. Furthermore, the rhythm was more pronounced, more stable, and less variable in the DDL condition. Conclusion:Our results indicate that DDL stimulation stabilizes circadian rhythms and leads to an improved behavioral repertoire in patients with severe brain injury. This highlights the importance of adequate room lighting in intensive care units and long-term care facilities as an adjunct therapeutic approach.