Both cluster headache and migraine have strong links to the circadian system, the internal clock that regulates body processes, according to a meta-analysis published in the journal of Neurology®, the medical journal of the American Academy of Neurology. The researchers also looked at studies on cluster headache and migraine and hormones related to the circadian system, including cortisol and melatonin. They found that both of these headache disorders are highly circadian at multiple levels, especially cluster headache. This reinforces the importance of the hypothalamus — the area of the brain that houses the primary biological clock — and its role in cluster headache and migraine. It also raises the question of the genetics of triggers such as sleep changes that are known triggers for migraine and are cues for the body’s circadian rhythm.