Phasic muscle activity during REM sleep in infancy-normal maturation and contrastive abnormality in SIDS/ALTE and West syndrome

The generation of phasic muscle activity during REM sleep is regulated by the brainstem. We proposed two sleep indices for phasic muscle activity during REM sleep, and examine their usefulness in assessing normal brainstem maturation and functional brainstem impairment during infancy. One - the dissociation index (DI) - seems to reflect maturation of the tonic inhibitory system functioning during REM sleep, and the other - % body movements in REMs bursts (%BMs-R) - to reflect that of the phasic one. In normal infants, DI showed a gradual, linear and significant increase with age, whereas %BMs-R showed a gradual and significant decrease with age. In infants with sudden infant death syndrome (SIDS) and one who had experienced apparent life-threatening events (ALTE), the DI values were lower than those in controls, although %BMs-R values were identical in the controls. In contrast, DI was variable in infants with West syndrome (WS), while %BMs-R exceeded normal values. The tonic inhibitory system seemed to be specifically involved in SIDS and ALTE, but the phasic inhibitory one in WS. Anatomical differences between these inhibitory systems are also discussed.