Sleep states and wakefulness in human infants: profiles from motility monitoring

Wakefulness and sleep states were determined from a single-channel analog recording of motility, including body movements and respiration. The subjects were normal infants ranging from 2 days to 4 months of age. First, one observer recorded behavioral states; at the same time respiration and motility was recorded from a pressure sensor under the baby. Subsequently, 4 judges used only the motility recordings to identify wakefulness and states of active, quiet, and active-quiet transitional sleep, for each successive 30-sec epoch. Inter-judge reliability ranged from a mean of 74.9 to 93.1 percent, assessed separately for each individual subject. Judge-observer validity was assessed over all subjects with agreement of r=0.90 for active sleep and r=0.92 for quiet sleep, and complete agreement on the occurrence and relative amount of wakefulness. Judge-observer validity was also assessed based on exact epoch-by-epoch agreement for each subject. Over the total observation agreement ranged from 70.3 to 89.0 percent, from 67.0 to 87.6 percent for active sleep, and from 59.3 to 93.0 percent for quiet sleep. Motility recording makes it possible to study the sequencing of states in infants during prolonged observational periods without instrumentation of the baby for the purpose of making the observations.