Aj. Lewy et al., THE HUMAN PHASE RESPONSE CURVE (PRC) TO MELATONIN IS ABOUT 12 HOURS OUT-OF-PHASE WITH THE PRC TO LIGHT, Chronobiology international, 15(1), 1998, pp. 71-83
Melatonin's timekeeping function is undoubtedly related to the fact th
at it is primarily produced during nighttime darkness; that is, melato
nin and light occur at opposite times. The human phase response curve
(PRC) to melatonin appears to be about 12h out of phase with the PRC t
o light. These striking complementarities, together with light's acute
suppressant effect on melatonin production, suggest that a function f
or endogenous melatonin is to augment entrainment of the circadian pac
emaker by the light-dark cycle. The melatonin PRC also indicates corre
ct administration times for using exogenous melatonin to treat circadi
an phase disorders.