Smiling asleep: A study of happy emotional expressions during adult sleep.

Human foetuses and newborns smile first during sleep, before they smile while awake and interacting with caregivers. Whether smiling persists during adult sleep, and expresses inner joy, is yet unknown. Smiles were looked for during night-time video-polysomnography combined with electromyography of the zygomatic and orbicularis oculi muscles in 100 controls, 22 patients with sleepwalking and 52 patients with rapid eye movement (REM) sleep behaviour disorder. Autonomous reactions (heart rate and level of vasoconstriction) and the presence of rapid eye movements were examined during smiles and laughs. On visual examination of the face video clips synchronous with zygomatic contraction, 8% of controls smiled while asleep (7% in REM sleep and 1% in non-REM sleep). Some patients with sleepwalking also smiled and laughed during N2 sleep and N3 parasomnia. Half of the patients with REM sleep behaviour disorder smiled and one-third laughed, mostly during REM sleep. The 173 happy faces included mild smiles (24.8%), open-mouth smiles (29.5%) and laughs (45.7%). More than half of the smiles were the Duchenne (genuine) type, including an active closure of the eyelids. Approximately half of the smiles and laughs were temporally associated with rapid eye movements. There was no increased heart rate variability during smiles and laughs. Two scenic behaviours including smiles and laughs suggested that the happy facial expression was associated with a happy dreaming scenario. Smiling and laughing occasionally persist during adult sleep. There are several lines of evidence suggesting that these happy emotional expressions reflect a true inner mirth.

Is there a common motor dysregulation in sleepwalking and REM sleep behaviour disorder?

This study sought to determine if there is any overlap between the two major non-rapid eye movement and rapid eye movement parasomnias, i.e. sleepwalking/sleep terrors and rapid eye movement sleep behaviour disorder. We assessed adult patients with sleepwalking/sleep terrors using rapid eye movement sleep behaviour disorder screening questionnaires and determined if they had enhanced muscle tone during rapid eye movement sleep. Conversely, we assessed rapid eye movement sleep behaviour disorder patients using the Paris Arousal Disorders Severity Scale and determined if they had more N3 awakenings. The 251 participants included 64 patients with rapid eye movement sleep behaviour disorder (29 with idiopathic rapid eye movement sleep behaviour disorder and 35 with rapid eye movement sleep behaviour disorder associated with Parkinson's disease), 62 patients with sleepwalking/sleep terrors, 66 old healthy controls (age-matched with the rapid eye movement sleep behaviour disorder group) and 59 young healthy controls (age-matched with the sleepwalking/sleep terrors group). They completed the rapid eye movement sleep behaviour disorder screening questionnaire, rapid eye movement sleep behaviour disorder single question and Paris Arousal Disorders Severity Scale. In addition, all the participants underwent a video-polysomnography. The sleepwalking/sleep terrors patients scored positive on rapid eye movement sleep behaviour disorder scales and had a higher percentage of 'any' phasic rapid eye movement sleep without atonia when compared with controls; however, these patients did not have higher tonic rapid eye movement sleep without atonia or complex behaviours during rapid eye movement sleep. Patients with rapid eye movement sleep behaviour disorder had moderately elevated scores on the Paris Arousal Disorders Severity Scale but did not exhibit more N3 arousals (suggestive of non-rapid eye movement parasomnia) than the control group. These results indicate that dream-enacting behaviours (assessed by rapid eye movement sleep behaviour disorder screening questionnaires) are commonly reported by sleepwalking/sleep terrors patients, thus decreasing the questionnaire's specificity. Furthermore, sleepwalking/sleep terrors patients have excessive twitching during rapid eye movement sleep, which may result either from a higher dreaming activity in rapid eye movement sleep or from a more generalised non-rapid eye movement/rapid eye movement motor dyscontrol during sleep.