Bhatt explains that brain cells work by sending electric signals to one another. When a migraine is triggered, a wave of electrical activity — called a cortical spreading depression (CSD) — spreads over the surface of the brain, suppressing the brain's normal electrical activity. If this suppression occurs in the part of the brain dedicated to vision, a visual aura will occur. If it happens in the part of the brain that controls tactile sense, a pins and needles type aura will occur. If it happens in the part of the brain that controls speech, an aphasic (language-related) aura will occur.

If the aura-causing CSD is the opening act of a play, the main event is sensitization of the nerve that controls pain in the face and head, the trigeminal nerve. "When this nerve and its tributaries and neurons get chemically primed, they start firing signals causing you to feel horrible pain," says Bhatt.

The thing is that these nerves are sending out pain signals even though no physically painful stimulus (say, getting hit in the head with a hammer) is present, but rather because migraineurs have that lowered threshold for abnormal biochemistry. In other words, these nerves get sensitized as a result of exposure to a trigger or some combination of triggers, says Bhatt.