The most prevalent neurological condition in the developed world, migraine is characterised by severe, recurrent headaches, with additional symptoms including nausea and sensitivity to light and sound. The frequency and duration of migraine attacks are variable: attacks may occur a few times a year or several times per month, while pain may last between four hours and three days. Approximately one third of sufferers experience an aura  a perceptual disturbance occurring before the migraines onset. There are numerous theories on the cause of migraines. The vascular theory posits that migraines are caused by problems with blood vessels in the brain. A more widely held view is that migraines result from low levels of the neurotransmitter serotonin in the brain. Prophylactic drug treatment, which prevents the onset of migraines, has declined in recent years, because of side effects and also improvements in medications treating an actual attack. Whereas older varieties of pain medication are potentially addictive, newer drugs called triptans work by reducing pain information travelling to the brain. Treatment plans typically include avoidance of known migraine triggers, such as diet, alcohol, and stress, as overuse of medication can lead to chronic rebound headaches. Not only do migraines have a debilitating effect on sufferers, they are also bad for the economy, with an estimated 25 million days lost from work every year in the UK alone.

Question: One third of migraines are preceded by a heightened sensitivity to light.
Options:
A. true, B. false, C. uncertain
Answer: "C"