Facial muscle activation during sleep and its relation to the rapid eye movements of REM sleep.

SUMMARY Facial muscle contractions (FMC) are a commonly observed feature during sleep stagesin human subjects. Previous studies have associated FMC to emotional expressionduring waking. Phasic features of rapid eye movement (REM) sleep, such as REMshave also been linked to an increase in limbic structure activity with a subsequentrelation to emotional dream content. We hypothesized that FMC would be morefrequent during REM sleep, and that FMC would correlate with the characteristicREMs of this sleep stage. The present study was designed to evaluate the density perminute of the phasic and sustained FMC of five facial muscles (frontalis, corrugator,orbicularis oculi, zygomatic major left and right) during all sleep stages, and to exploretheir relation with REMs density in six healthy participants during an 8 h sleeprecording. Results showed a significant increase in FMC of all recorded muscles duringREM sleep, both in frequency and duration. Additionally, as expected, during REMsleep there was a positive correlation among the facial muscles and between these andREMs. Nevertheless, although associated in number, both features (FMC and REMs)were never simultaneous. Our results suggest that limbic activation during REM sleepmay be responsible for the enhancement of facial muscle activity, which may beconsistent with the theoretical perspective of a higher emotional activity during REMsleep.keywords EMG activity, facial muscles, rapid eye movements, REM sleep