REM-Sleep Deviations and Their Role for Psychiatric Disorders

Keywords

REMS; Dreaming; Psychopathology

Abbreviations

REMS: Rapid Eye Movement Sleep; ADHD: Attention- Deficit/Hyperactivity Disorder; IQ: Intelligence Quotient; EEG: Electroencephalographic; PLM: Periodic Limb Movements; RLS: Restless Legs Syndrome; SDB: Sleep-Disordered Breathing; RBD: REMS Behavior Disorder

Editorial

Rapid Eye Movement-Sleep (REMS) and its neurophysiological signatures and brain activation patterns have been shown to support many cognitive and psychological adaptive functions, including consolidation of emotional memory [1], resolution of affect and emotional processing [2], consolidation, stabilization and elaboration of previously transformed memories [3,4], procedural memory and implicit or motor learning [4,5], and heuristic creativity [6]. However, the precise functions of REMS remain elusive, and REMS’ physiological processes and associated dreaming state may have more complex functional significance than proposed so far [7,8]. These latter functions refer to less well recognized adaptive processes. First, REMS and dreaming were proposed to generate an innate virtual model of the world, which is proposed to promote predictive coding or Bayesian inference/complexity reduction in wakefulness [7]. Second, it was assumed that the periodic occurrence of REMS and associated dreaming may be regarded as a recurrent adaptive interference that may incorporate previously encoded and consolidated memories into a broader vital context comprising residuals of hypotheses testing, related emotions, basic needs, and individual genetic traits [8]. Third, REMS dreaming state also has been proposed to sub-serve mental activity that is oriented to changes in environment or of the subjects view and approach to these, according to personal needs without definite probability forecast to the outcomes, but with a regular consideration of the outcomes in the process of active behavior - the so called search activity, which acts differentially in relation to norm and psychopathology [9].

From a developmental perspective, it is to be noted that infants have much more REMS proportion which descends through childhood and adolescence, than adults [10]. It has been proposed that this developmental decrease in REMS support brain maturation through internally-generated stimulation of neuronal assembles and genetic programming [11].

Collectively, the above mentioned REMS and dreaming functions suggest strongly that deviations of REMS timing and proportion, and REMS physiological signatures and dreaming state during either maturation or later in life can lead to worsened cognitive, emotional and psychosocial adaptation. This in turn could result in occurrence of various psychiatric disorders and psychopathological conditions [12].

Factors that could produce REMS deviations are many. First, inappropriate developmental decrease in REMS is considered as a prerequisite for numerous common child and adolescent psychiatric disorders [13,14,15]. For example, we have previously demonstrated that youths with Attention-Deficit/Hyperactivity Disorder (ADHD) displayed more REMS compared with healthy peers, and whilst the REMS proportion in ADHD patients was associated positively with inattention and negatively with performance Intelligence Quotient (IQ), in the healthy peers it was associated negatively with inattention and positively with performance IQ [16]. A more recent study showed that whereas decreased REMS theta (4 Hz – 8 Hz) Electroencephalographic (EEG) power was associated with worsened emotional memory in ADHD children, this REMS EEG signature was associated positively with emotional memory in healthy subjects [17]. Further, a literature review indicated that dominance of tics and motor activities such as Periodic Limb Movements (PLM) and Restless Legs Syndrome (RLS) in REMS among children and adolescents with Tourette syndrome may lead to impaired daytime adaptive functions [18]. Last but not at least, two reviews substantiated of many experimentally-driven data showed that 1) nightmares in REMS may be predictors of many psychiatric conditions during adolescence [13], and 2) brain activation patterns during wakefulness and REMS are very similar in common youth psychiatric disorders compared to typically developing children, thus suggesting a dream-like state during wakefulness in these patients [15]. Next, Sleep-Disordered Breathing (SDB), PLM and RLS were shown to dominate during REMS, especially in child psychiatric disorders and aging [13,18,19,20]. Whilst this leads to REMS fragmentation, the exact daytime behavioral consequences are still less well understood. Similarly, REMS Behavioral Disorder (RBD) in association with PLM and RLS, which is most common in elderly with Parkinson or Alzheimer’s diseases, can also deteriorate REMS and its dreaming state [20]. However, it is so far unclear whether the behavioral deficits in REMS disorders like SDB, PLM, RLS, and RBD are illness-specific, medication-induced, or may result simply from REMS fragmentation.

Likewise, treatment approaches in neuropsychiatric diseases and mood and sleep disorders also may lead to interrupted and/ or reduced REMS, thus hampering its natural functions for the successful adaptation. For example, dopamine agonists, selective serotonin and norepinephrine reuptake inhibitors reduce REMS significantly [15,18]. A psychotherapeutic approach in treatment of sleep disorders and related psychopathological conditions, such as lucid dreaming [21], has been shown to change the normal REMS EEG signatures and brain activity and the associated dreaming state [22]. However, the intact REMS features are mandatory for the normal functions that REMS and the associated dreaming is proposed to support [1,2,3,4,7,8,9,11].

In conclusion, deviant changes in REMS could certainly affect its natural functional significance for the successful adaptation. Such deviant REMS patterns may result from the following reasons. (1) Inappropriate maturation of sleep-wake cycle and particularly, the developmental REMS decrease. (2) REMS-specific disorders, especially in association with developmental psychopathologies and age-related morbid conditions. (3) Pharmaco- or psychotherapeutic approaches (lucid dreaming) in treatment of sleep and neuropsychiatric disorders. But the adverse effects of some of these REMS deviations have been overlooked frequently in sleep medicine. Bringing the attention of sleep medicine specialists to these issues could improve treatment of neuropsychiatric diseases associated with REMS deviation.

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