Origins of Migraine Pain
The exact source of migraine headache pain is somewhat controversial. The old theory, put forward by Dr. Harold G.Wolff back in the 1930’s and 40’s, is that vasodilatation (enlarging) arteries caused the head pain associated with a migraine headache and the throbbing nature of the headache is the pulse of the heart. Wolff based his theory on the following:
- Observation of one particular migraine patient who had a hole in her skull because of a prior brain injury.The hole became depressed prior to a migraine headache and then would enlarge during the headache.The shift in size was attributed to blood flow changes.
- Manual pressure on the arteries to the brain during the headache reduced the pain. (Don’t try this at home.)
- Vasoconstrictors (drugs which make the arteries smaller) reduce migraine headaches.
- Injections of some vasodilators caused migraine.
- Manipulation of the temporal artery in some migraine patients reproduced their migraine.
Given the testing available during the time of his work, Wolff’s theory was rapidly accepted. However, his theory is probably not the cause of migraine headaches, or at least is only a partial explanation of what is happening during a migraine headache.
The Modern Theory
Dr. Mike Moskowitz performed most of the groundbreaking work for the neurogenic theory of migraine and the information presented here is summarized from a number of his articles and lectures. If one looks at the nerve supply to the pain sensitive structures in the head (dura, venous structures, etc), they are innervated by a meshwork of nerves that are mostly from the first division of the trigeminal nerve. Each nerve goes to a wide area of the dura but in general, the nerves do not cross the midline. These nerves are interwoven around the blood vessels and are closely associated with mast cells. In the brain, the cells of the trigeminal nerve project to centers in the brain stem as well as areas of the brain responsible for nausea. On your skin, the first division of the trigeminal nerve is responsible for sensation from an area above your eye through the top of your head.
During a migraine, axons release substances that cause blood vessels to vasodilate and nearby mast cells to release additional substances that trigger pain and also cause blood vessels to vasodilate. These substances cause the blood vessels to leak fluid and therefore an inflammatory reaction occurs. The entire process is described as neurogenic inflammation. These released substances also serve to make the nerve more sensitive to previously innocuous stimulus such as the mechanical distention of the pulse. Because the nerves transmitting the pain signals from the affected area also supply sensation to the area above the eye, the pain is referred to the temporal or forehead region. Every pulse of the artery causes the nerve to fire giving the pain the throbbing quality that is so characteristic of the migraine headache.