Can observers link dream content to behaviours in rapid eye movement sleep behaviour disorder? A cross‐sectional experimental pilot study

Summary Motor activity in rapid eye movement (REM) sleep behaviour disorder (RBD) has been linked to dream content. Systematic and controlled sleep laboratory studies directly assessing the relation between RBD behaviours and experienced dream content are, however, largely lacking. We aimed to investigate whether a link can be established between RBD behaviours and dream content when both are systematically sampled in a controlled setting. We investigated six patients with Parkinson syndrome and RBD who underwent 2–3 nights of video–polysomnographic recording during which they were awakened from REM sleep (10 min after the onset of the second and successive REM periods). Spontaneous free‐worded dream reports and a structured dream questionnaire were obtained. Video recordings of motor manifestations were each combined with four dream reports, and seven judges had to match the video clip with the correctly reported dream content from a choice of four possibilities. Of the 35 REM sleep awakenings performed, a total of 17 (48.6%) motor‐behavioural episodes with recalled dream content were obtained. The mean of correctly identified video‐dream pairs was 39.5% (range 0–100%). Our data showed that reported dream content can be linked to motor behaviours above chance level. Matching accuracy was affected mainly by the clarity of dream reports and the specific nature of movements manifest in video recordings.