Experimentally induced rhythmic jaw muscle activities during non‐rapid eye movement sleep in freely moving guinea pigs

Abstract

Rhythmic jaw muscle activities frequently occur during non‐rapid eye movement sleep in patients with sleep bruxism. The present study aimed to investigate the response characteristics of the masticatory rhythm generation during non‐rapid eye movement sleep in animals. Eleven guinea pigs were surgically prepared for polygraphic recordings by electromyography, electrooculography, electroencephalography and electrocardiography with the implantation of a stimulating electrode. Repetitive electrical microstimulations at three intensities were applied to the corticobulbar tract under freely moving conditions. The rhythmic electro‐myographic responses of the digastric and masseter muscles were scored and analysed. Changes in cortical electro‐encephalographic power and heart rate in association with these stimulations were quantified. Microstimulations to the corticobulbar tract induced rhythmic jaw muscle activities in digastric muscles, occasionally with masseter activities during wakefulness and non‐rapid eye movement sleep. The response rate of rhythmic jaw muscle activities was significantly lower (p < 0.01) and the response latency was significantly longer (p < 0.01) during non‐rapid eye movement sleep than during wakefulness. At higher stimulus intensities, the response rate increased and response latency decreased. The mean burst intervals of the digastric and masseter muscles were similar regardless of vigilance states and stimulus intensities. Induced rhythmic jaw muscle activities during non‐rapid eye movement sleep were followed by a transient decrease in delta power and increases in beta power and heart rate. During non‐rapid eye movement sleep, the masticatory motor system is able to generate rhythmic outputs to the jaw muscles in response to facilitatory inputs although the responsiveness was decreased from wakefulness.

A lack of specific motor patterns between rhythmic/non-rhythmic masticatory muscle activity and bodily movements in sleep bruxism

“…These results suggest that a cardiac-motor sequence related to transient arousal is shared by RMMA and NSMA, regardless of the accompanying bodily movements. However, human and animal studies have demonstrated that RMMA and NSMA are not directly triggered by arousals [39][40][41]. As shown in the present study, otherwise healthy subjects with SB showed an increased frequency of RMMA but normal NSMA in typical sleep macro-and microstructures.…”

Sleep architecture as a candidate for phenotyping sleep bruxism: A narrative physiological review

“…Therefore, RMMA may be generated by a unique physiological mechanism(s) within multiple neural pathways generating distinct patterns of rhythmic jaw movements 25,43 . Animal studies attempted to induce rhythmic jaw movements by stimulating the cortical masticatory area and its descending tracts during sleep and found that the responsiveness of masticatory CPG to the stimulation was lower during non‐REM sleep than wakefulness 48,49 . Therefore, the excitability of neurons generating rhythmic jaw movements is periodically decreased during non‐REM sleep, whereas sleep arousal pressure is absent.…”