You love to say you're a night owl, yet your body is telling a very different story. Your circadian rhythms, the routine changes in your behavioral, mental and physical functions that occur over the course of a day, are regulated by a tiny area of the brain commonly known as your 'biological clock.' The suprachiasmatic nucleus (SCN) is shaped like a pine cone, but is about the size of a grain of rice, though it contains about 20,000 neurons.