Developmental changes in phasic sleep parameters as reflections of the brain-stem maturation: polysomnographical examinations of infants, including premature neonates.

To gain understanding of brain-stem maturation during the early stages of life, we used polysomnography to examine 32 normal infants aged 33-184 conceptional weeks. Our study focused on the developmental aspects of the phasic sleep parameters, REM density and body movement, and the executive system. REM densities were highest in infants aged 36-38 conceptional weeks. The numbers of gross movements and localized movements (LMs) on chin muscle decreased with age; whereas, those of the twitch movements (TMs) on chin muscle increased. Ratios of the TMs to the total number of LMs and TMs (tentatively designated dissociation indexes because of the close relation between LMs and TMs on surface electromyograms) showed significant increases that paralleled the increase in age. We speculate that the dissociation index is a quantitative reliable sleep parameter which reflects brain-stem maturation.