Discharge patterns of human genioglossus motor units during sleep onset.
OBJECTIVE
Multiunit electromyogram recordings of genioglossus have demonstrated an abrupt reduction in the muscle's activity at sleep onset. Recent evidence from single motor unit recordings indicates that the human genioglossus muscle consists of motor units with a variety of discharge patterns. The aim of the present study was to determine the effect of sleep onset on the activity of individual motor units as a function of their particular discharge pattern.


METHODS
Genioglossus activity was assessed using intramuscular fine-wire electrodes via a percutaneous approach. Sleep onsets (alpha-to-theta transitions) were identified and the genioglossus electromyogram recordings analyzed for single motor unit activity.


METHODS
Sleep research laboratory.


METHODS
Sleep and respiratory data were collected in 8 healthy subjects (6 men).


RESULTS
One hundred twenty-seven motor units were identified: 23% inspiratory phasic, 45% inspiratory tonic, 4% expiratory phasic, 9% expiratory tonic, 16% tonic, and 3% other. Approximately 50% of inspiratory units (phasic and tonic) ceased activity entirely at sleep onset, whereas those inspiratory units that continued to be active showed a reduction in the proportion of each breath over which they were active. However, the rate of discharge of inspiratory units during the period they did fire was not altered. In contrast, tonic and expiratory units were unaffected by sleep onset, maintaining their discharge pattern over the alpha-to-theta transition.


CONCLUSIONS
Central control of inspiratory motoneuron output differs from that of tonic and expiratory units during sleep onset, suggesting that the maintenance of airway patency during sleep may become more reliant on the stiffening properties of tonic and expiratory modulated motor units.
Wilkinson
Vanessa
V
Department of Psychology, University of Melbourne, Parkville, Australia.
Malhotra
Atul
A
Nicholas
Christian L
CL
Worsnop
Christopher
C
Jordan
Amy S
AS
Butler
Jane E
JE
Saboisky
Julian P
JP
Gandevia
Simon C
SC
White
David P
DP
Trinder
John
J
D000328:Adult; D001696:Biomechanical Phenomena; D004567:Electrodes, Implanted; D004569:Electroencephalography; D004576:Electromyography / Q000295:instrumentation; D004585:Electrooculography; D005260:Female; D006801:Humans; D001239:Inhalation; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D012890:Sleep / Q000502:physiology*; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis; D014851:Wakefulness / Q000502:physiology