 Rather, endogenous melatonin serves to internalize light cues, making melatonin responsible for modulating neuroendocrine functions.The suprachiasmatic nucleus, or SCN, is a small region within the anterior hypothalamus of the brain that is responsible for orienting the organism’s internal measurement of time to external time cues like daylight.The SCN was first identified to be the "circadian pacemaker" responsible for generating circadian rhythms in 1972.