The cause behind the generating of the brainstem in this fashion is unknown. Professor Peter Goadsby from the UK, for example, demonstrated that the generator for cluster, is located in the region of the brain called the hypothalamus. The hypothalamus is located immediately above the pituitary gland and is one area in which the nervous and hormonal systems of the body interact. It receives information and responds by prompting the pituitary appropriately. The circadian rhythm synchronizes biological processes such as sleep, to the day-night cycle occasioned by the rotation of the earth.
Cluster headache does indeed, have cyclical characteristics.
Attacks tend to be grouped in a series of short bursts of pain lasting about 30 minutes, often occurring in the middle of the night, continuing periodically over a period of several weeks, and then disappearing until the same time the following year. The previous was taken from an article by Dr. Marek Gawel and taken from a write-up on the 9th International Headache Society Congress in Barcelona, June 1999. Professor Michael Moskowitz, MD.,head of neurology at Harvard, who's work led to Sumatriptan, and does a lot of the research into headache etiology, hypotheses' are referenced. In a nutshell, the source of cluster HAs is thought to originate from the cavernous sinus on the side of the headache. The periodicity is about the only thing that is a bit puzzling according to Mathew.