Stability and changes in sleep regulation. A longitudinal study from 3 months to 3 years

The goal of the study was to examine the developmental course of sleep consolidation from infancy to preschool. The sleep of 50 healthy infants aged 3 months was recorded, at home, with actigraphs (computerised activity monitors). Follow-up recordings were carried out at 6, 9, 12, 20, and 42 months (due to attrition and occasional technical failures, complete sleep records were not available for all subjects at all ages). The main findings were that by 12 months, nocturnal sleep is well organised; nevertheless, sleep continues to become less fragmented and more efficient beyond the first year. The child's level of motor activity during sleep, and the overall sleep efficiency were moderately stable across time. In contrast, sleep duration and the number of nightwaking episodes were unstable from 3 to 42 months of age. Taken together, the continuity and change in the group trajectory of sleep maturation, as well as the stability and the periodic instability in the individuals' rank across time, may be interpreted to reflect the interplay among constitutional, maturational, and experiential factors.