A four-year follow-up study of the sleep-wake cycle of an infant

The sleep-wake behavior of a boy was investigated from 5 weeks up to four years of age. The protocol consisted of recording waking and sleep states by direct observation by his mother and eventually by the housemaid. Data were divided in 7-day segments and these segments were then divided in 10-minute binary information about asleep or awake. Fast Fourier Transform (FFT) was applied to obtain the frequency spectrum for each 7-day epoch, and the results were submitted to statistical test for the identification of significant component frequencies. Data were also divided in 21-day epochs and 30-minute windows in order to detect infradian periodicities. Overall rhythmicity increased during the four years with the circadian component as the major contribution after the fifth week of life. The semicircadian and the 8-hour components had maximum contributions during the second and third years, and the 6-, 5- and 4-hour components during the first year. After the beginning of his attendance to school, the boy showed a decrease of the semicircadian component, explained by the absence of an afternoon nap and an increase of the circadian component. Infradian periodicities were not found during the whole four years.