REM sleep behaviour disorder: a window on the sleeping brain

This scientific commentary refers to ‘Ictal SPECT in patients with rapid eye movement sleep behaviour disorder’, by Mayer et al. (doi:10.1093/brain/awv042). REM sleep behaviour disorder (RBD) continues to serve as an increasingly instructive window on the sleeping brain. The identification of RBD in humans in 1986 was predicted by Michel Jouvet’s 1965 feline model produced by bilateral perilocus coeruleus lesions and subsequently replicated in the rat (Schenck et al. , 2002). Initially, human RBD was felt to be a curious and fascinating experiment in nature resulting in the isolated absence of atonia during REM sleep, permitting the ‘acting out of dreams’ (or, the ‘dreaming out of acts’). As more diverse groups of patients were studied, and as patients with RBD were followed over time, a number of interesting facts and correlations emerged. One of these was that the overwhelming majority (up to 90%) of patients with what initially appeared to be ‘idiopathic’ RBD would eventually develop a neurodegenerative disease (often following a delay of decades), particularly one of the synucleinopathies (Parkinson’s disease, dementia with Lewy bodies, or multiple system atrophy) (Iranzo et al. , 2014). Furthermore, waking motor manifestations of bradykinesia and hypophonia in patients with comorbid Parkinson’s disease and RBD were markedly improved during movements and vocalizations within episodes of RBD (De Cock et al. , 2007). Similar findings were reported for RBD associated with multiple system atrophy (De Cock et al. , 2011), with enhanced facial expression, improved speech and faster/stronger movements in REM sleep compared to wakefulness. These improvements were unlikely to be due to enhanced dopamine transmission because patients with multiple system atrophy are poorly …