SLEEP RHYTHMICITY IN PREMATURE-INFANTS - IMPLICATIONS FOR DEVELOPMENTAL STATUS

Ultradian and diurnal rhythms in premature infants were investigated b y assessing cyclicity of quiet sleep (QS) and the diurnal distribution of this cyclicity. The sleep of 49 preterm infants was recorded in th e hospital for three successive 24-hour periods at 36 weeks conception al age (CA), and 42 of the infants were recorded in the home for two 2 4-hour periods when they were 6 months old. Sleep was recorded nonintr usively by means of the motility monitoring system, which does not req uire instrumentation of the subject. Cyclicity was assessed using a pr ocedure that permits assessment of significance as well as degree of c yclicity. Twenty of the 49 infants at the preterm age and 37 of the 42 infants at 6 months had sleep episodes with significant cyclicity. Me an cyclicity scores increased from 0.61 to 0.81 over age, but the cycl e length of approximately 60 minutes did not change. There was no evid ence for individual consistency across the two ages in any of the slee p or cyclicity measures. Evidence for diurnal differences was present from the preterm period. At both ages, there were far more analyzable sleep episodes and higher cyclicity at night. At the preterm period, c yclicity measures were negatively related to indices of advanced perin atal status as well as 6-month mental scores; at 6 months, the cyclici ty measures were positively related to perinatal measures as well as m ental scores. These results indicate the necessity for different inter pretations of periodicity at the preterm and later age. When the QS an d active sleep (AS) components of the sleep cycle were examined, QS wa s not found to be related to mental scores at either age; whereas, the AS component was related to mental scores at both ages-but negatively at the preterm age and positively at 6 months. The results indicate t hat AS, in this context, is an indicator of more general neurobehavior al competence, but in reverse directions at the two ages. These result s suggest that different regulatory processes are controlling the temp oral sequencing of states over the developmental course. It is propose d that preterm cyclicity is a response to ongoing stress in the preter m infants, while cyclicity at 6 months reflects more directly central neural competence.