PRCs in Circadian Rhythms
In circadian rhythm research, a PRC illustrates the relationship between a treatment's time of administration and the treatment's effect on a circadian rhythm. Normally, the body's various physiological rhythms will be synchronized within an individual organism (human or animal). The sleep–wake cycle is the most familiar of these rhythms; for humans, a treatment designed to affect circadian rhythms will most often be intended to adjust sleep timing, by either delaying it to later in the day (night), or advancing it. Extreme morning people may want to delay their sleep timing; extreme evening chronotypes may wish to advance it.
A PRC is a graph showing, by convention, time of the subject's endogenous day along the x-axis and the amount of the phase shift (in hours) along the y-axis. The curve has one peak and one nadir in each 24 hour cycle. Relative circadian time is plotted vs. phase shift magnitude.
The two common treatments used to shift the timing of sleep are light therapy, directed at the eyes, and administration of the hormone melatonin, usually taken orally. Either or both can be used daily. Each of these treatments has its own PRC which will vary according to the species being studied; its shape may also vary individually, just slightly. The magnitude is dose-dependent. The discussions below are restricted to the human PRCs for the chronobiotics light and melatonin.
Read more about this topic: Phase Response Curve
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