The Development of Circadian Rhythms in Human Infants

value of above 0.5 for R squared was recorded as the week a mature, robust clock
gene pattern appeared.
Sleep was investigated in two ways. The initial analysis involved reporting the week
the maximum sleep efficiency of the infant was achieved.
Further analysis replaced week of maximum sleep efficiency with the week the infant
had the maximum number of immobile phases of 1 minute and the maximum
percentage of 1 minute immobile minutes. This was felt to be more sensitive and
reflect more closely intrinsic infant sleep rather than sleep efficiency in which the
calculation included external factors such as the time infants are placed to bed by the
care givers.
Using mean values, the timing of emergence of first maximum surge in morning
cortisol secretion occurred first at 8.17 weeks of age (p=0.0015). Night time
melatonin had first appearance of diurnal variation and at 9.10 weeks. Maximum
infant sleep efficiency occurred simultaneously at 9.40 weeks of age (p=0.9585).
Temperature maturation occurred next at 10.79 weeks (p=0.0156). Timing of
maximum amplitude of peripheral clock gene expression and timing of week of best
fit to sinusoidal curve wave form was at 10.86 weeks.
These temporal relationships are illustrated in Figure 10.1.
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