MATURATION OF MOTILITY AND MOTOR INHIBITION IN RAPID-EYE-MOVEMENT SLEEP

Objective: To describe the age-related changes in the number of moveme nts in rapid eye movement (REM) sleep, and to quantify the functional maturation of motor inhibition. Study design: Gross movements, phasic mentalis muscle activity (PMMA), and a new index that expressed the sh ortness of PMMA (the proportion of short PMMA among all PMMA) were exa mined cross-sectionally in 87 healthy children from premature babies t o preadolescents by means of a single (all-night) polysomnography. Res ults: The incidence of gross movements and long PMMA decreased with ag e, whereas that of short PMMA increased with age. The new index exhibi ted an age-related increase, with the highest correlation with age amo ng sleep parameters examined, and reached an adult level after 6 years of age. Conclusion: We found that the age-related reduction of PMMA d uration, which was expressed by a new index, occurred in parallel with the maturation of the inhibitory system that is tonically activated d uring REM sleep. We named this index the tonic inhibition index and co ncluded that the neuronal system involved in motor inhibition during R EM sleep was still maturing during early childhood. We propose the ton ic inhibition index as a useful quantitative indicator for the maturit y of the inhibitory system.