Sleep states of infants monitored in the home: Individual differences, developmental trends, and origins of diurnal cyclicity

Abstract

Using an automated procedure for sleep recording, the sleep of 20 healthy full-term infants was monitored for 24-hour periods in the home once a week during the 1st to 5th weeks of life. A pressure-sensitive mattress, placed in the infant's crib, was used for recording analog signals from respiration and body movements. The motility signals were recorded on a single channel of a small Oxford 24-hour recorder. In the laboratory, the recorded signals were processed and computer scored for states using a pattern recognition program which employs a template matching procedure. For each 30-s epoch, the state was scored as either active sleep (AS), quiet sleep (QS), active-quiet transitional sleep (AQ), sleep-wake transition (TR), or wakefulness (WA). Significant individual differences were found for each state parameter. Significant developmental trends over weeks were found: AS decreased and QS increased as a function of changing bout lengths in these states. The number of state changes per hour was constant over the 5 weeks. State patterns obtained by this automated recording procedure did not differ from those obtained by direct behavioral observations. Diurnal differences in the state distributions for 12-hour day and night periods were found, with more wakefulness occurring during the daytime. The infants showed a significant linear increase in wakefulness during the daytime, while wakefulness during the night remained relatively stable across weeks. Even during periods when they were in the crib, the infants spent significantly more time awake during the daytime. These highly organized characteristics of infants' states were apparent from the earliest postnatal age despite variations in activities that typically occur in the home. The findings confirm the validity and potential usefulness of the sensor mattress recording procedure.