Difficult morning awakening from rapid eye movement sleep and impaired cognitive function in delayed sleep phase disorder patients

•This study explored difficult morning awakening in delayed sleep phase syndrome.•Polysomnography and cognitive testing were used in an overnight sleep study.•It is thought that difficult awakening is related to slow wave sleep.•Inability for patients to wake up by alarm clock was observed in relation to rapid eye movement sleep.•Both morning cognitive impairment and persistent impairment were observed.

ObjectivesDifficult awakening is a key symptom of delayed sleep phase disorder (DSPD), but no studies have quantified awakening thresholds in a sleep laboratory. This study assessed whether cognitive function was impaired after awakening and whether difficult awakening was associated with specific polysomnographic features such as slow wave sleep stage N3.MethodsNine patients with DSPD and nine sex- and age-matched healthy controls were included. Polysomnography was performed at our university hospital from midnight. An alarm clock was activated at 07:00 with sound intensity increasing from 72 to 104 dB. Participants performed a continuous performance test (CPT) the previous afternoon and immediately upon awakening.ResultsThree DSPD patients and zero controls did not wake up to the maximum 104 dB alarm sound; all three patients were in rapid eye movement (REM) sleep when the alarm clock went off (difference in proportions, P = 0.047). In patients, CPT reaction time was prolonged in the morning compared to the afternoon [analysis of variance (ANOVA) interaction, P = 0.01]. DSPD patients made more omission errors than controls regardless of time of the day (ANOVA main effect, P = 0.046).ConclusionDifficult awakening from slow wave sleep was not observed. A subgroup of DSPD patients may have a severe problem waking up from REM sleep. DSPD patients may also have a state-like impairment in cognitive function in the morning and a trait-like impairment not depending on time of day, compared to normal sleepers.