Clinically, patients often report that changes in sleep can bring on migraine headaches. One study found there was first human migraine gene linked to enzyme involved. Patients report that altering sleep pattern increases their migraine headaches. There is also a link between sleep pattern and the most severe vascular headaches such as cluster headaches, in which headache attacks awaken patients at night. The cluster headache demonstrates strong diurnal and seasonal periodicity with patients being awaken within a few hours of falling asleep. Observation had found that too little of too much sleep can trigger migraine headaches, and data links certain brain centers that have control of circadian and sleep mechanism with migraine pathophysiology.