If you've ever felt groggy the morning after traversing time zones,you can thank the temporary mismatch between your body's 24-hour circadian rhythm and your fresh local time. In mammals, this rhythm is governed on a neuronal and hormonal level by the suprachiasmatic nucleus, or a tiny region of the brain's nestled directly above the two optic nerves. But it's not just a long flight that can throw us out of whack. As we age,the suprachiasmatic nucleus, or SCN, or tends to exhibit a weaker circadian rhythm,which can result in sleep disorders, metabolic syndrome and depression.
Source: phys.org