Phase response curve
![Phase response curves for light and for melatonin administration](/Images/godic/202502/02/PRC-Light+Mel4201.png")
![The time shown on the x-axis is vague: dawn – mid-day – dusk – night – dawn. These times do not refer to actual sun-up etc. nor to specific clock times. Each individual has her/his own circadian](/Images/godic/202502/02/Human_PRC4202.png")
A phase response curve (PRC) illustrates the transient change in the cycle period of an oscillation induced by a perturbation as a function of the phase at which it is received. PRCs are used in various fields; examples of biological oscillations are the heartbeat, circadian rhythms, and the regular, repetitive firing observed in some neurons in the absence of noise.