Migraines are defined as regularly occurring, intense headaches that typically affect one side of the head. Unlike other types of neuropathic pain, neuronal hyperexcitiation that spreads across the cortex does not particularly arise from injury. This wave of activity stimulates stimulates trigeminal nerves that normally signal damage in blood vessels, causing the experience of pain. Another theory states that the release of a neuropeptide called CGRP by the trigeminal nerves causes the pain.