It is difficult to study migraine in the way other diseases are studied. There is no animal model. Animals may well have migraines, but since they can't talk to us, it is hard to know if and when they are experiencing one. There are no differences in the brains of migraineurs compared with non-migraineurs seen on autopsy or in regular CT or MRI scans. Long ago, neurologists noted that blood vessels in the scalp, such as the superficial temporal artery in the temple, were often dilated in people during a migraine. Sometimes even the carotid artery in the neck would become sore (carotidynia). The walls of blood vessels in the scalp and the coverings of the brain are richly supplied with pain-sensitive nerve endings, although the brain itself is not sensitive to pain (you can cut into it while the patient is awake without pain). Blood flow studies showed that during an aura, blood flow was decreased and during the headache phase, blood flow was increased. Therefore, it was proposed that migraine was a disease of blood vessels, and the pain was due to over-expansion of them. More recent studies have shown that although the blood flow to the brain is less, the arteries are not constricted during the aura. It is now believed that the cause of migraine is an abnormality of the biochemicals in the brain known as neurotransmitters. These are responsible for the electrical depolarization of the brain cells, and are the means by which brain cells communicate with each other by passing electrical signals. The transmitters serotonin and norepinephrine are especially implicated in migraine. Disturbances of these neurotransmitters cause electrical activity in the brain to be depressed. The depressed or depolarized region often spreads contiguously from one part of the brain to another. Patients with auras note the spreading or changing of the aura as the wave of depolarization spreads across their cerebral cortex, causing the disfunction manifesting itself as visual, sensory, or motor disturbances. These neurotransmitters also may alter the brain's pain control system (endorphins) causing hypersensitivity to pain. The abnormalities of the central nervous system that lead to migraines appear to be inherited. Most patients with migraine have a parent or sibling who is also affected. Other diseases involving the neurotransmitters, such as depressive mood disorders, are more common in migraine patients. The gene(s) is apparently an "autosomal dominant" which means that an affected parent will have a 50% chance of passing the tendancy on to each child. Everyone who inherits the tendancy, however, does not suffer from migraines. Other influences from the environment (foods, head injuries, etc.) and hormonal (e.g. estrogen) influences may cause a susceptible person to have migraine attacks while another person without such influences may be spared despite having inherited the condition. Although we have found out a lot about the causes of migraine, much is still unknown, especially the details. Migraine is not a simple disease, which makes it fascinating to brain researchers.