Cortical activation during sleep predicts dream experience in narcolepsy.

In drug-free adults with narcolepsy type 1, successful dream recall after naps is linked to a more activated brain state during both REM and NREM sleep. Using scalp EEG, the study found that recall was associated with lower delta power over centro-parietal areas in both sleep stages, higher beta power in those areas during NREM, and a lower delta/beta ratio across most scalp locations during NREM. These results suggest that a more desynchronized, activated electrophysiological milieu promotes dream recall, and that parietal areas are important not only for generating dream experiences but also for the memory processes that enable recall.

Study at a glance

Abstract

Narcolepsy type 1 widely affects the architecture of sleep with frequent fast transition to REM sleep at both nighttime and daytime sleep onset. The occurrence of repeated sleep onset REM periods over the Multiple Sleep Latency Test offers a unique opportunity to identify EEG patterns predictive of successful dream recall after short periods composed of only REM or NREM sleep. It also permits to disentangle state- from trait-like differences in dream recall, by using a within-subjects design. A consecutive series of 115 first-diagnosed drug-free adult narcolepsy-type 1 patients underwent Multiple Sleep Latency Tests and were asked after each nap opportunity if they had or had not a dream experience. Scalp EEG power and a specific index of cortical activation (delta/beta power ratio), obtained from naps of 43 patients with both presence and absence of dream recall in the same sleep stage, were compared separately for REM and NREM sleep. Successful dream recall was associated with an increased EEG desynchronization in both REM and NREM over partially overlapping cortical areas. Compared to unsuccessful recall, it showed (1) lower delta power over centro-parietal areas during both stages, (2) higher beta power in the same cortical areas during NREM, and (3) lower values in the delta/beta ratio during NREM in most scalp locations. A more activated electrophysiological milieu in both REM and NREM sleep promotes dream recall, strengthening the notion that the parietal areas are crucial not only in generating dream experience, as shown in brain-damaged patients, but also in the memory processing leading to recall.