The masseter muscle is involved in the complex and coordinated oromotor behaviors such as mastication during wakefulness. The masseter electromyographic (EMG) activity decreases but does not disappear completely during sleep: the EMG activity is generally of low level and inhomogeneous for the duration, amplitude and intervals. The decreased excitability of the masseter motoneurons can be determined by neural substrates for NREM and REM sleep. The masseter EMG activity is increased in association with the level of arousal fluctuations within either sleep state. In addition, there are some motor events such as REM twitches, swallowing and rhythmic masticatory muscle activity (RMMA), whose generation might involve the additional activation of specific neural circuits. Sleep bruxism (SB) is characterized by exaggerated occurrence of RMMA. In SB, the rhythmic activation of the masseter muscle can reflect the rhythmic motor inputs to motoneurons through, at least in part, common neural circuits for generating masticatory rhythm under the facilitatory influences of transient arousals. However, it remains elusive as to which neural circuits determine the genesis of sleep bruxism. Based on the available knowledge on the masseter EMG activity during sleep, this review presents that the variety of the masseter EMG phenotypes during sleep can result from the combinations of the quantitative, spatial and temporal neural factors eventually sending net facilitatory inputs to trigeminal motoneurons under sleep regulatory systems.

中文翻译：

---

睡眠期间的咬肌肌电活动和睡眠磨牙症。

咬肌参与清醒过程中的复杂而协调的口腔运动行为，例如咀嚼。睡眠期间，咬肌肌电图（EMG）活性降低，但并未完全消失：在持续时间，振幅和间隔中，EMG活性通常水平较低且不均匀。咬肌运动神经元兴奋性的降低可以由NREM和REM睡眠的神经底物确定。在任一睡眠状态下，咬肌的肌电活动均与唤醒波动的水平相关。此外，还有一些运动事件，例如快速眼动痉挛，吞咽和咀嚼节律性肌肉活动（RMMA），其产生可能涉及特定神经回路的额外激活。睡眠磨牙症（SB）的特征是过度出现RMMA。在SB中 咬肌的节律性激活可以反映出运动神经元的节律性运动输入，至少部分是通过在短暂唤醒引起的促进作用下产生咀嚼性节律的常见神经回路。然而，关于哪些神经回路决定睡眠磨牙症的成因仍然难以捉摸。基于对睡眠过程中咬肌EMG活动的现有知识，该评价表明，睡眠过程中咬肌EMG表型的多样性可能是由于定量，空间和时间神经因素的组合而最终向睡眠中的三叉神经运动神经元发送了促进性输入监管系统。在短暂唤醒的促进影响下产生咀嚼节律的常见神经回路。然而，关于哪些神经回路决定睡眠磨牙症的成因仍然难以捉摸。基于对睡眠过程中咬肌EMG活动的现有知识，该评价表明，睡眠过程中咬肌EMG表型的多样性可能是由于定量，空间和时间神经因素的组合而最终向睡眠中的三叉神经运动神经元发送了净促进性输入监管系统。在短暂唤醒的促进影响下产生咀嚼节律的常见神经回路。然而，关于哪些神经回路决定睡眠磨牙症的成因仍然难以捉摸。基于对睡眠过程中咬肌EMG活动的现有知识，该评价表明，睡眠过程中咬肌EMG表型的多样性可能是由于定量，空间和时间神经因素的组合而最终向睡眠中的三叉神经运动神经元发送了促进性输入监管系统。