REM sleep behavior disorder rhythms

Abstract

REM sleep behavior disorder (RBD) is an intriguing parasomnia that is characterized by repeated dream enactment associated with increased muscle tone and twitch burst activity in REM sleep. This article explores a unique perspective on the relationship of RBD with various neurophysiological rhythms. We describe the clinical and polysomnographic characteristics of this disorder with diagnostic considerations. Arousal disorders simulating RBD, including Non-REM Sleep Arousal Parasomnias, Obstructive Sleep Apnea and Periodic Limb Movement Disorder, are also described. The pathophysiological basis is discussed with reference to the physiological substrates of RBD subtypes. Periodic Leg Movements associated with RBD, Rhythmic Masticatory Muscle Activity (Sleep Bruxism) and Oromandibular Myoclonus Associated with RBD, Rhythmic Movement Disorder associated with RBD, interface of RBD with epileptic abnormalities, and sleep spindles are also elaborated upon. REM sleep in relation to ultradian sleep rhythmsSleep occurs in ultradian cycles of Non-Rapid Eye Movement (NREM) sleep followed by Rapid Eye Movement sleep, ranging from 90-120 minutes, alternating throughout the night. Typically, it comprises of 3-5 cycles per night. The duration of later REM sleep periods is longer than those noted in the earlier half of the night. REM sleep density, which is a measure of frequency of rapid eye movements in REM sleep, is also higher in the last third of the night. REM sleep has been hypothesized to be involved in memory consolidation through processing between the hippocampus and neocortex [1]. Neurophysiological monitoring of sleep requires recording of the electroencephalogram (EEG), electrooculogram (EOG) and electromyogram (EMG) [2]. Polysomnographic characteristics of normal REM sleepThe REM stage of sleep is normally characterized by low voltage intermixed frequency EEG waves, rapid eye movements, and markedly decreased skeletal muscle tone [2]. REM sleep is also called paradoxical sleep where EEG is desynchronized. On polysomnographic (PSG) monitoring, REMs are characterized as irregular sharp conjugate eye movements with initial duration <500ms. Saw-tooth waves form a distinctive pattern occurring in REM sleep, which are temporally associated with REMs. They are triangular waves with frequency of 2-6 Hz with maximum amplitude in central leads [2]. An example of a 30-sec epoch of REM sleep is shown in Figure 1A.In feline models, ponto-geniculo-occipital (PGO) spikes have been described to originate in the pons, propagate to the lateral geniculate nucleus, and then are observed in the occipital cortex. It is hypothesized that they are related to saw-tooth waves as PGO bursts occur with high probability in relation to REMs [3]. Clusters of PGO-like subthalamic waves occurring before or during REMs have also been recorded in humans, associated with enhancement of fast oscillatory subthalamic activity [4]. PGO waves have been conventionally regarded as neurophysiological correlates of dreaming [4]. REM sleep behavior d...