Facial muscle contractions during REM sleep and its association to emotional dreamed content

Abstract

Introduction Facial muscle contractions (FMC) are features commonly associated with emotional expression during waking, yet poorly studied during sleep. Recent studies show a pattern in both healthy subjects and patients with major depression during sleep in which FMC have a significantly higher frequency and amplitude during Rapid Eye Movement (REM) sleep than in non-REM (NREM) sleep and that they are associated to the Rapid Eye Movements (REMs) in this sleep stage. Notably, REMs are also associated with emotional dream mentation (EDM). Yet, the possible functional relationship between FMC and EDM, remains unexplored. This study analysed FMC of the corrugator and zygomatic major – two facial muscles typically associated with emotional expression – and explores possible temporal correlations of EDM in healthy subjects during REM sleep. Additionally, it examined the interaction between FMC and REMs with EDM. Materials and methods Two 8 h sleep recordings were obtained from 6 female volunteers. Facial EMG recordings were obtained from the corrugator supercilii and zygomatic major (left and right) muscles. Sleep was scored using the standard AASM criteria. On the second night, FMC were visually measured. Experimental awakenings exploring EDM (through narration, rating of a dream scale, and Dreams Qualified Report) were performed during REM sleep stages that lasted at least three minutes, they were determined by a FMC that lasted more than 100 ms and by the amplitude of any facial muscle that exceeded by 500% the background EMG activity. Additionally, experimental awakenings were performed during NREM and REM sleep stages without FMC. Following sleep recordings, FMC and REMs were quantified and analyzed for possible correlations between them. EDM global scores were gauged by exploring their correlation coefficients. Results Periods with FMC and REMs were associated to higher levels of EDM in healthy subjects as compared to periods without FMC. Moreover, EDM modality (e.g. happy vs. anxious) was linked to certain muscle activation (e.g. higher FMC of zygomatic vs. lower corrugator). Conclusion The present study shows that during REM sleep with FMC (vs. periods without FMC) the corrugator, zygomatic muscles and REMs are associated to EDM. Additionally, FMC were differentially associated to emotional modality according to the activated facial muscle. Altogether, these findings are consistent with theoretical perspectives of higher emotional variations during REM sleep associated to dream content. Implications are discussed. Acknowledgements Isidoro Camacho Garcia Carlos Jimenez Rodriguez Carlos Camacho Garcia.