The Development of Circadian Rhythms in Human Infants

1.5.3 Ontogeny of Temperature Control
When a baby is first born, there is thought to be little difference in day and night time
core body temperature. After a few weeks of age, a day and night difference begins to
emerge, with night time temperature falling within the first four hours of sleep. The
maximum fall is to 36.7ºC. The infant does not have a fully mature circadian rhythm
at this point. As the baby gets older, just prior to sleep onset, there is an appreciable
increase in the depth of drop in core body temperature just prior to sleep onset within
the first four hours. Once the temperature is able to fall to below 36.5ºC, the infant is
described to be exhibiting a „mature‟ or „adult-like‟ temperature rhythm (Lodemore et
al., 1991).
Once this mature rhythm has been established there is no further drop in core body
temperature during night time sleep. Therefore if subsequent measurements are done
on an infant once „maturity‟ has taken place the temperature plots look the same. This
pattern in the core body temperature is stable throughout the rest of the childhood and
adulthood. The core body temperature will only rise if an individual is exposed to an
infection or has immunisation (Lodemore et al., 1992, Jackson et al., 1994, Jackson et
al., 2001). Similar descriptions of core body temperature patterns in night time sleep
have been given in other studies. In addition Glotzbach and Weinert have also
demonstrated changes in sleep-wake levels as well as heart rate, occurring over the
same period (Glotzbach et al., 1994, Weinert et al., 1994).
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