Circadian Rhythms in Children

Circadian rhythms are generated by an endogenous circadian timing system. The biological clock, a key component of the circadian timing system, is anatomically located in the suprachiasmatic nucleus of the anterior hypothalamus and its functioning is grounded on a genetic-based negative feedback loop mechanism. Circadian rhythms are entrained to the 24-hour cycle by so-called Zeitgebers or synchronizers that can be environmental such as the dark/light cycle, social such as school start time, or biological such as melatonin. One of the most widely investigated circadian rhythms is the sleep/wake cycle, the organization of which can be understood within the theoretical framework of the two-process model of sleep regulation. Looking at this model from a developmental perspective, it can be supposed that sleep (S) or the homeostatic process may be preponderant over the circadian (C) process in early life because homeostasis is an intrinsic basic function of living beings aimed at avoiding possible interference from the environment. The C process, on the contrary, is supposed to help the S process to gradually tune with environmental changes. It is probable that this is the reason why the C process undergoes a progressive development that is completed at the end of adolescence, changing the balance between the two processes, and becoming preeminent compared with the S process. After the C process completes its maturation, it starts to progressively weaken with age, leading to a new balance between the two processes.