REM Sleep Instability – A New Pathway for Insomnia?

Abstract

Chronic insomnia afflicts approximately 10% of the adult population and is associated with daytime impairments and an elevated risk for developing somatic and mental disorders. Current pathophysiological models propose a persistent hyperarousal on the cognitive, emotional and physiological levels. However, the marked discrepancy between minor objective alterations in standard parameters of sleep continuity and the profound subjective impairment in patients with insomnia is unresolved. We propose that "instability" of REM sleep contributes to the experience of disrupted and non-restorative sleep and to the explanation of this discrepancy. This concept is based on evidence showing increased micro- and macro-arousals during REM sleep in insomnia patients. As REM sleep represents the most highly aroused brain state during sleep it seems particularly prone to fragmentation in individuals with persistent hyperarousal. The continuity hypothesis of dream production suggests that pre-sleep concerns of patients with insomnia, i. e., worries about poor sleep and its consequences, dominate their dream content. Enhanced arousal during REM sleep may render these wake-like cognitions more accessible to conscious perception, memory storage and morning recall, resulting in the experience of disrupted and non-restorative sleep. Furthermore, chronic fragmentation of REM sleep might lead to dysfunction in a ventral emotional neural network, including limbic and paralimbic areas that are specifically activated during REM sleep. This dysfunction, along with attenuated functioning in a dorsal executive neural network, including frontal and prefrontal areas, might contribute to emotional and cognitive alterations and an elevated risk of developing depression.

Slow dissolving of emotional distress contributes to hyperarousal

“…To do so, we systematically evaluated the association of all items of the NSR's extended implementation of the Dream Recall Frequency Scale (DRFS; Methods) (30) with the REM sleep arousal index (31) obtained from the second of two nights of PSG in 32 people [19 female and 13 male, mean (SD) of 35.8 (9.0) y of age], of whom 16 had been diagnosed with Insomnia Disorder (ID). Metaanalysis showed that variables reflecting disruption of sleep continuity are the most robust PSG signatures in insomnia (16), especially fragmentation of REM sleep (5,17). Although less specific to insomnia, fragmentation occurs in NREM sleep as well (5).…”

“…resolving of emotional distress and whether hyperarousal, in fact, represents the resulting accumulation of this distress. Of note, hyperarousal is not only present across waking and sleep in people suffering from MDD (21) but is also of key importance in the pathophysiology of primary insomnia (6,(22)(23)(24) and a premorbid characteristic of people vulnerable to insomnia (5,25).…”

“…It therefore appears highly relevant to understand the mechanisms involved in the role of insomnia in disturbed emotion regulation (2). The present study addresses the roles of restless rapid-eye-movement (REM) sleep (5) and chronic physiological arousal (6), which are characteristic of both insomnia and MDD.…”

“…Two studies suggest that this fragmentation is most pronounced in REM sleep and may contribute to the development of the sleep characteristics of MDD, like increased eye movement density (5,17). We use the term "restless REM sleep" here to refer to REM sleep with a high number of phasic events, including arousals and eye movements.…”

Sleep stability and transitions in patients with idiopathic REM sleep behavior disorder and patients with Parkinson's disease

“…comorbid insomnia; a common symptom in PD. Riemann et al (Riemann et al, 2012) reports REM sleep instability as an objective measure for primary insomnia patients compared to good sleeper controls. Although they measure REM sleep instability differently than us (number of manually scored micro-arousals and awakenings per hour of REM sleep compared to our fully data-driven method), we cannot rule out insomnia as causative for the lower REM sleep stability.…”