Insomnia: Restless REM sleep promotes nocturnal mentation and hyperarousal by interfering with the resolution of emotional distress

Objectives: Insomnia is a major risk-factor for the development of major depression. One of the main characteristics involved could be hyperarousal. More recently, rapid-eye-movement (REM) sleep was shown to be highly fragmented in insomnia. We hypothesized that restless REM sleep interferes with the overnight resolution of emotional distress, and that the resulting unresolved distress accumulates into chronic hyperarousal. Methods: 1199 volunteers filed out questionnaires on insomnia severity, hyperarousal, self-conscious emotional distress, and a specific proxy for restless REM sleep: nocturnal mentation (validated in 32 polysomnographically assessed participants; selective fragmentation: R = 0.57, P <0.001; and eye movement density: R = 0.46, P <0.01). Results: Insomnia severity was associated with the type of nocturnal mentation that reflects restless REM sleep (β = 0.31, P <10-26). Specifically, emotional distress lasting overnight occurred more frequent with insomnia severity (β = 0.29, P <10-23). This was not the case for emotional distress resolved within hours (β = -0.02, P = 0.41). Notably 62.3% of the direct association between restless REM sleep and hyperarousal could be explained by increased frequency of experiencing long-lasting emotional distress. Conclusions: The findings indicate that specifically the overnight resolution of emotional distress is disrupted by an underlying process that shows as restless REM sleep in polysomnography and as nocturnal mentation in questionnaires. The disruption appears key to the development of hyperarousal. Intervention studies may target REM sleep stabilization for the treatment of insomnia, depression and posttraumatic stress disorder.