Abstract
Rhythmic masticatory muscle activity (RMMA) of jaw-closing muscles can occur during sleep in healthy human subjects although its physiological significance remains unknown. If RMMA is exaggerated, however, the condition is regarded as sleep bruxism, which can be associated with clinical problems. Until recently, mechanisms generating sleep bruxism had not been well understood. Recent studies have reported that episodes with RMMA mostly occur in light (non-rapid eye movement) NREM sleep during the ascending phase of NREM sleep cycles, and that the genesis of episodes is secondary to a sequence of arousal-oromotor events; cardiac and cortical activation precedes jaw-opening suprahyoid muscle contraction, and is followed by rhythmic jaw-closing muscles activation. Since neurophysiological mechanisms generating RMMA have yet to be studied in animals, masseter muscle activity in guinea pig was recorded during sleep and analyzed. Among various muscle bursts occurring during sleep, some episodes with repetitive masseter muscle activity in NREM sleep were associated with a brief increase in heart rate and a transient decrease in delta EEG activity. This presentation provides an overview of current knowledge of RMMA during sleep in humans and introduces a challenge in developing a putative animal model for sleep bruxism. [J Physiol Sci. 2007;57 Suppl:S23]
