The suprachiasmatic nucleus (SCN) is a nucleus in the hypothalamus and is so named because it resides immediately above the optic chaism. It consists of two nuclei that are separated by the 3rd ventricle. Its principle function is to create the circadian rhythm, which regulates the body functions over the 24 hour day. It consists of various cell types, some which possess ability for light-induced gene expression. Melanopsin-containing cells in the retina have a direct connection to suprachiasmatic nucleus via the so-called retino-hypothalamic tract. The SCN sends information to other hypothalamic nuclei and the pineal gland to modulate body temperature and hormone production such as cortisol and melatonin. Rats with damage to the SCN sleep "erratically" (i.e. they do not show night-day rhythm).