Editing Cluster headache (section)

===Hypothalamus===
A review suggests that the [[suprachiasmatic nucleus]] of the [[hypothalamus]], which is the major biological clock in the human body, may be involved in cluster headaches, because cluster headaches occur with diurnal and seasonal rhythmicity.<ref>{{cite journal |last=Pringsheim |first=Tamara |title=Cluster headache: evidence for a disorder of circadian rhythm and hypothalamic function |journal=Canadian Journal of Neurological Sciences |date=February 2002 |volume=29 |issue=1 |pages=33–40 |doi=10.1017/S0317167100001694 |pmid=11858532|doi-access=free }}</ref>

[[Positron emission tomography]] (PET) scans indicate the brain areas which are activated during attack only, compared to pain free periods. These pictures show brain areas that are active during pain in yellow/orange color (called "pain matrix"). The area in the center (in all three views) is activated only during cluster headaches. The bottom row [[voxel-based morphometry]] shows structural brain differences between individuals with and without CH; only a portion of the [[hypothalamus]] is different.<ref>{{cite journal |doi=10.1007/s11916-007-0010-1 |pmid=17367592 |title=Cluster headache: A review of neuroimaging findings |journal=Current Pain and Headache Reports |volume=11 |issue=2 |pages=131–6 |year=2007 |last1=Dasilva |first1=Alexandre F. M. |last2=Goadsby |first2=Peter J. |last3=Borsook |first3=David |s2cid=35178080 }}</ref>