At the start of a migraine, an external or internal trigger causes neurons in the brain to fire abnormally. These triggers are vast and varied, and include lack of sleep, increase in stress, dietary choices, strong scents, shift in weather, or hormonal changes during a woman’s menstrual cycle. Those abnormally firing neurons cause hyperexcitability in various regions of the brain, leading to symptoms that affect the senses. You may experience nausea, sensitivity to light and sound, or difficulty with motor skills and speech, although symptoms vary for every sufferer. Some sufferers even experience aura either a visual disturbance that appears as lights or lines, or a temporary loss of vision. Scientists believe that the head pain associated with migraines may begin because of a drop in the body’s levels of the neurotransmitter serotonin, which causes the nervous system to release other chemicals called neuropeptides. Low serotonin levels cause the blood vessels surrounding the brain to dilate, and it’s this expansion that can lead to throbbing in your head, often concentrated on one side.