Jaw-opening reflex and corticobulbar motor excitability changes during quiet sleep in non-human primates.
OBJECTIVE
To test the hypothesis that the reflex and corticobulbar motor excitability of jaw muscles is reduced during sleep.


METHODS
Polysomnographic recordings in the electrophysiological study.


METHODS
University sleep research laboratories.


METHODS
The reflex and corticobulbar motor excitability of jaw muscles was determined during the quiet awake state (QW) and quiet sleep (QS) in monkeys (n = 4).


RESULTS
During QS sleep, compared to QW periods, both tongue stimulation-evoked jaw-opening reflex peak and root mean square amplitudes were significantly decreased with stimulations at 2-3.5 × thresholds (P < 0.001). The jaw-opening reflex latency during sleep was also significantly longer than during QW. Intracortical microstimulation (ICMS) within the cortical masticatory area induced rhythmic jaw movements at a stable threshold (≤ 60 μA) during QW; but during QS, ICMS failed to induce any rhythmic jaw movements at the maximum ICMS intensity used, although sustained jaw-opening movements were evoked at significantly increased threshold (P < 0.001) in one of the monkeys. Similarly, during QW, ICMS within face primary motor cortex induced orofacial twitches at a stable threshold (≤ 35 μA), but the ICMS thresholds were elevated during QS. Soon after the animal awoke, rhythmic jaw movements and orofacial twitches could be evoked at thresholds similar to those before QS.


CONCLUSIONS
The results suggest that the excitability of reflex and corticobulbar-evoked activity in the jaw motor system is depressed during QS.
Centre for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
Dongyuan
D
Yao
Gilles J
GJ
Lavigne
Jye-Chang
JC
Lee
Kazunori
K
Adachi
Barry J
BJ
Sessle
D000818:Animals; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D007568:Jaw / Q000502:physiology*; D008252:Macaca fascicularis / Q000502:physiology; D008253:Macaca mulatta / Q000502:physiology; D017286:Polysomnography; D011712:Pyramidal Tracts / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D012890:Sleep / Q000502:physiology*; D012894:Sleep Stages / Q000502:physiology