Evaluation of jaw and neck muscle activities while chewing using EMG-EMG transfer function and EMG-EMG coherence function analyses in healthy subjects

Abstract

This study aims to quantitatively clarify the physiological features in rhythmically coordinated jaw and neck muscle EMG activities while chewing gum using EMG-EMG transfer function and EMG-EMG coherence function analyses in 20 healthy subjects. The chewing side masseter muscle EMG signal was used as the reference signal, while the other jaw (non-chewing side masseter muscle, bilateral anterior temporal muscles, and bilateral anterior digastric muscles) and neck muscle (bilateral sternocleidomastoid muscles) EMG signals were used as the examined signals in EMG-EMG transfer function and EMG-EMG coherence function analyses. Chewing-related jaw and neck muscle activities were aggregated in the first peak of the power spectrum in rhythmic chewing. The gain in the peak frequency represented the power relationships between jaw and neck muscle activities during rhythmic chewing. The phase in the peak frequency represented the temporal relationships between the jaw and neck muscle activities, while the non-chewing side neck muscle presented a broad range of distributions across jaw closing and opening phases. Coherence in the peak frequency represented the synergistic features in bilateral jaw closing muscles and chewing side neck muscle activities. The coherence and phase in non-chewing side neck muscle activities exhibited a significant negative correlation. From above, the bilateral coordination between the jaw and neck muscle activities is estimated while chewing when the non-chewing side neck muscle is synchronously activated with the jaw closing muscles, while the unilateral coordination is estimated when the non-chewing side neck muscle is irregularly activated in the jaw opening phase. Thus, the occurrence of bilateral or unilateral coordinated features in the jaw and neck muscle activities may correspond to the phase characteristics in the non-chewing side neck muscle activities during rhythmical chewing. Considering these novel findings in healthy subjects, EMG-EMG transfer function and EMG-EMG coherence function analyses may also be useful to diagnose the pathologically in-coordinated features in jaw and neck muscle activities in temporomandibular disorders and whiplash-associated disorders during critical chewing performance.

Coherence of jaw and neck muscle activity during sleep bruxism

“…Although this present study used muscle coherence as outcome measure, studies using muscle co‐activation as outcome measure support the current findings on masticatory and neck muscles . However, several methodological issues make the current findings not directly comparable with these co‐activation studies.…”

“…27 The current programmes used to estimate coherence require long-term rhythmic activities, such as those present in tremors or chewing movements. 10,17,28 However, bruxism involves short-term episodes that alternate uncontrollably in the form of tonic, phasic and/or mixed activation. 29 For this reason, a modified analysis programme for coherence analysis of phasic and mixed episodes during SB based in the widely used Welch's method 27 was prepared by the Department of Neurology of the Radboudumc and used in the present study.…”

“…The used coherence analysis estimates the power of a signal at different frequencies and is based on the concept of converting a signal from the time domain to the frequency domain . The current programmes used to estimate coherence require long‐term rhythmic activities, such as those present in tremors or chewing movements . However, bruxism involves short‐term episodes that alternate uncontrollably in the form of tonic, phasic and/or mixed activation .…”

“…[7][8][9] During mastication, this rhythmic opening and closing of the jaw is well coordinated by masticatory as well as neck muscles. 10 During sleep, similar rhythmic masticatory muscle activity (RMMA) can be seen in healthy subjects as part of normal sleep microarousals, 11 but with higher prevalence in patients with SB. 12 RMMA can be divided into phasic activity (such as tooth grinding), tonic activity (such as clenching) and mixed activity (combination of phasic and tonic) and could be influenced in frequency, duration and intensity by multiple endogenous and exogenous factors, such as psychological and lifestyle factors or multimorbidity.…”

“…Voluntary rhythmic masticatory muscle activity, like mastication, is controlled by a central pattern generator (CPG) in the brainstem . During mastication, this rhythmic opening and closing of the jaw is well coordinated by masticatory as well as neck muscles . During sleep, similar rhythmic masticatory muscle activity (RMMA) can be seen in healthy subjects as part of normal sleep microarousals, but with higher prevalence in patients with SB .…”