Suprachiasmatic nucleus

The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for regulating sleep cycles in animals. Reception of light inputs from photosensitive retinal ganglion cells allow it to coordinate the subordinate cellular clocks of the body and entrain to the environment. The neuronal and hormonal activities it generates regulate many different body functions in an approximately 24-hour cycle.

The SCN also interacts with many other regions of the brain. It contains several cell types, neurotransmitters and peptides, including vasopressin and vasoactive intestinal peptide.

Disruptions or damage to the SCN has been associated with different mood disorders and sleep disorders, suggesting the significance of the SCN in regulating circadian timing.