Neurophysiological insights into the pathophysiology of REM sleep behavior disorders: a review

Rapid eye movement (REM) sleep behavior disorder (RBD) is a clinical condition characterized by an intermittent or complete loss of muscle atonia and an increase of phasic muscular activity during REM sleep (or Stage R), leading to complex nocturnal motor behaviors. Correct and early diagnosis is important because RBD may lead to serious injuries and is a well-treatable disorder. Since the characteristic electrophysiologic finding in patients with RBD is the increased electromyographic tone during REM sleep/Stage R, simultaneous video/polysomnography recording is essential for diagnosing this parasomnia. Moreover, several neurophysiological techniques have been used to improve our knowledge and understanding of this troubling sleep disorder. We reviewed the most important studies employing quantitative electroencephalography, event-related potentials, transcranial magnetic stimulation, brainstem reflexes and cortico-muscular coherence analysis. All these neurophysiological techniques have proven to provide a valuable tool to gain insight into the pathophysiological mechanisms underlying RBD. The review concludes with a brief discussion on the possible future implications for improving therapeutic approaches.