Functional Imaging in Primary Headache Disorders
Over the past two decades, the development of new functional neuroimaging techniques has improved our understanding of the brain events underlying several primary headache disorders. In migraine and cluster headache, the advent of these techniques has shifted the emphasis in pathophysiological research away from the vessel and back to the brain.

Attempts to investigate the pathophysiology of primary headache disorders have been hampered by their transient and unpredictable nature. The lack of any demonstrable gross pathological change or any other readily identifiable biomarker has slowed progress in headache research for decades. These factors combined with a paucity of effective treatments stigmatized headache sufferers, relegating migraine and other headache disorders in the minds of many to the category of psychosomatic complaint. At the start of the last quarter of the 20th century, there was a limited (at best) understanding of even the most common and devastating primary headaches such as migraine and cluster headache (CH). Most of the available data came from investigations of vessels, structures much more easily studied than the brain. Understandably, the predominant theory of headache was based on a vascular hypothesis and any head pain that throbbed was called a "vascular" headache. The rise of new functional imaging techniques, however, in the closing decades of the 20th century revolutionized our understanding of headache pathophysiology and shifted the emphasis away from the vessel and toward the brain.