Migraine headache is a result of specific changes within the brain. It causes severe head pain that is often accompanied by sensitivity to light, sound, or smells. Other types of headaches can also cause severe pain, and not all headaches are migraines. For example, some people describe the pain of cluster headaches as the worst pain they have experienced. The exact cause of migraines is not known. Changes in neurotransmitter levels within the brain are thought to play a role.
United States Government - Independent Agencies. Independent Agencies of the Unites States government are tasked with administering the law as regarding specific areas such as the environment, social security, and veteran affairs. These Agencies are expert in the area they manage and are generally headed by a Board or Commission, while a few, such as the EPA, are headed by a single Administrator.
Washington, D.C. The government of the United States of America is the federal government of the republic of fifty states that constitute the United States, as well as one capital district, and several other territories.