Development of REM sleep atonia

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Abstract
Objectives – To study the functional development of neuronal systems that suppress muscle activity, we quantified the chronological change of atonia in rapid‐eye‐movement sleep (REMS). Methods – REMS atonia was quantified by the tonic and phasic inhibition indices (TII and P1I). TII indicates the shortness of chin muscle activity, whereas PII standardizes the simultaneous occurrence of chin muscle activity and bursts of rapid eye movements. TII and PII were calculated in REMS of 135 polysomnographical recordings obtained in healthy humans from premature babies to a 77‐year‐old man. Results – TII increased significantly with age, while PII decreased significantly. TII reached an adult level at preadolescence, while PII at early infancy. Conclusion – Human nervous systems involved in both tonic and phasic inhibition in REMS raise their activities with age. Since TII and PII reach adult levels at different ages, suppression of muscle activity is hypothesized to be mediated through at least 2 independent systems in humans.