DEVELOPMENT OF HUMAN SLEEP AND WAKEFULNESS RHYTHM DURING THE FIRST 6 MONTHS OF LIFE - DISCONTINUOUS CHANGES AT THE 7TH AND 12TH WEEK AFTER BIRTH

The development of the human circadian rhythm of sleep and wakefulness during the first 6 months of life was investigated in ten (7 male and 3 female) full-term infants. The mothers were asked to fill out the s leep logs of their babies over the six months after birth. On the basi s of the sleep logs, the authors scored each 15 min unit of sleep as ' one' and that of wakefulness as 'zero.' The strings of data were analy zed by the autocorrelation method to investigate the development of th e circadian rhythmicity of each infant's sleep during each week. Then the authors classified the patterns of correlogram from the 2nd to the 26th week using cluster analysis. The analysis classified these patte rns into three groups. The first group (pattern A) showed scarce evide nce of a circadian component. The second one (pattern B) had a promine nt circadian component. The last one (pattern C) was characterized by its prominent circadian positive peak and negative peak around 12 hrs periodicity, which represent very scarce amount of daytime sleep. Almo st all the infants changed their patterns from A to B around the 7th w eek, then some of the infants changed their patterns from B to C at th e 12th week. The first discontinuous change in the sleep and wakefulne ss circadian rhythm around the 7th week coincides with the period of a n important reorganization in sensorimotor behavior, which many other studies suggest. The second discontinuous change might be considered a s the first sign of individual differences concerning daytime naps or daytime sleepiness.