Can observers link dream content to behaviours in rapid eye movement sleep behaviour disorder? A cross-sectional experimental pilot study.
BACKGROUND REM sleep behavior disorder (RBD) is characterized by vigorous sleep motor activity associated with dream mentation. Patients with RBD frequently report action-filled and violent dreams. OBJECTIVE To systematically assess dream characteristics and daytime aggressiveness in patients with RBD and controls. METHODS Forty-nine patients with polysomnographic-confirmed RBD diagnosis and 71 age- and sex-matched controls were asked to recall the most recent dreams and to complete the Aggression Questionnaire (AQ). Forty-one patients with RBD (81.6%; 36 men, 5 women; mean age: 67.5 +/- 7.5 years) and 35 controls (49.3%; 30 men, 5 women; mean age: 69.1 +/- 5.9 years) were able to remember their dreams and a total of 98 (RBD) and 69 (controls) dreams were collected in the two groups. Verbatim dream descriptions were scored and analyzed according to the Hall and Van De Castle method. RESULTS Patients with RBD showed a higher percentage of dream with at least one aggressive episode (DWA) than controls (66% vs 15%; p < 0.00001), a higher aggression/friendliness interaction ratio (86% vs 44%; p < 0.0001), and a greater frequency of animal characters (19% vs 4%; p = 0.0001). In contrast to controls, no patient with RBD had dreams with elements of sexuality (0% vs 9%; p < 0.0001). The two groups did not differ in total AQ scores, except for a lower score on the physical aggressiveness subscale in patients with RBD compared to control subjects (16.5 +/- 6.4 vs 20.4 +/- 8.3; p = 0.034). No correlation was observed between dream aggressiveness and age, duration, or frequency of RBD symptoms. CONCLUSIONS Dreams in patients with REM sleep behavior disorder were characterized by an elevated proportion of aggressive contents, despite normal levels of daytime aggressiveness. Dreams with aggressiveness and the known excessive phasic muscle activity during REM sleep may be related to the hyperactivity of a common neuronal generator.