A quantitative analysis of phasic and tonic submental EMG activity in human sleep.

Submental muscle activity and slow-wave activity in the EEG (mean power density in the 0.75-4.5-Hz band) were determined for consecutive 20-sec epochs in 34 all-night recordings of human sleep. Muscle activity was quantified by calculating the statistical variance of the digitized electromyogram (EMG). The tonic level of muscle activity was lower in REM sleep (REMS) than in nonREMS, and higher in the first nonREMS episode but an increasing trend within all subsequent nonREMS episodes. EEG slow-wave activity increased in the first part of all nonREMS episodes and decreased in the first part of all REMS episodes. The absolute or relative difference in muscle activity between two consecutive 20-sec intervals was used for defining EMG arousals. The density of arousals did not differ significantly among nonREMS episodes. Weak and moderate arousals showed an increasing density over consecutive REMS episodes. While arousals were uniformly distributed within REMS episodes, they were concentrated at the beginning and the end of nonREMS episodes.