Spectral electroencephalography profile of rapid eye movement sleep at sleep onset in narcolepsy type 1

Background and purpose: The sleep-onset rapid eye movement (REM) period (SOREMP), the hallmark of narcolepsy, may be a specific state and not the simple anticipation of REM sleep. Methods: We analyzed the electroencephalographic spectral content in untreated patients with narcolepsy type 1 (NT1) during the sleep-onset period (SOP) and during nocturnal REM sleep in two consecutive nocturnal recordings from 31 patients with NT1 (mean age 34 ± 15 years, 18 males) and a single nocturnal recording from 36 controls (mean age 38 ± 13 years, 21 males). The SOP was defined as the first 10 min starting at the beginning of the first epoch of any sleep stage, and further divided into two consecutive 5-min periods (SOP-1 and SOP-2); 1 min of artifact-free quiet wakefulness after lights-off was identified as well as 5 min of REM sleep in the middle of the night and another 5 min during the last REM sleep period. Electroencephalographic spectral analysis was performed using the C3/A2 channel. Results: The SOP-1 and, more strikingly, SOP-2 had significantly less delta and sigma activity in patients with NT1 in the SOREMP condition versus both controls and patients with NT1 without SOREMP. SOP-2 also showed less theta and alpha activity. Conversely, sigma and beta activity were more represented during SOREMP compared with the nocturnal REM period in patients with NT1. Conclusions: The analysis of the SOP supports the concept that SOREMP is a different state compared with both nocturnal REM sleep and non-REM sleep onset.