The suprachiasmatic nucleus (SCN) is morphologically divided into two subdivisions, ventrolateral and dorsomedial parts. The retinohypothalamic tract (RHT) is important for the syncronization of circadian rhythms, since environmental light-dark information is transmitted to the circadian clock from the retina through the RHT. The RHT, which was known to exist in nonmammalian vertebrates, loomed as a possible candidate for the light information pathway. We examined the mechanism of the circadian rhythms of feeding behavior in addition to daily changes in energy metabolism. It would be interesting to know whether the SCN includes all of the multiple oscillators responsible for splitting clusters. In addition, it was shown that circadian rhythms recovered when intact SCN was transplanted either into or around the third cerebral ventricle of rats whose circadian rhythms were eliminated by electrolytical SCN lesions. Spontaneous internal desynchronization does not always take place when humans or other animals are in conditions which lack a circadian environmental cycle.