How much the internal clock determines daily behavioral cycles

What is it about?

Living organisms have a clock in their cells that orchestrates many cellular and behavioral activities according to the time of the day, e.g. daily wake/sleep cycle. The internal clock (also called the circadian clock) orchestrates this 24-hour rhythm even in constant conditions, e.g. in an underground bunker without any light cues or an alarm clock. The length of a full cycle of a particular rhythm in a constant condition (such as the underground bunker) is called the circadian period, or simply period. The time of the day of a certain daily behavior is called phase of entrainment, or simply phase. Many pathological phenomena that are important to human health are related to phase; e.g. jet leg and sleep disorders. Traditionally, the phase is understood as a manifestation of period in cyclic conditions. When someone is a morning type person, one assumes the person has a shorter period. When someone is a night owl type person, one assumes the person has a longer period. However, there is experimental data that cannot be explained by assuming this simple relationship between period and phase. The authors explored if other relationships exist between period and phase and found two examples: a short period with a delayed phase and a long period with an advanced phase. The authors also developed a mathematical model to explain all possible relationships between period and phase.

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Why is it important?

The mechanisms of circadian period have been studied extensively compared to those of phase of entrainment. The current study showed that the relationships between period and phase are complex, and not linear. Understanding how phase is determined in a cyclic environment will lead us to address the real-life pathological health problems caused by a misaligned circadian clock. The mathematical model predicted that there are two parameters that determine the relationship between period and phase.

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