A team of US researchers have found a link between migraines and how sodium is distributed through the brain, a finding that could be key to future research on treatments for millions of affected people.

Using high-powered magnets at the lab, essentially a high-powered magnetic resonance imaging, the team scanned rats' brains as they experienced migraines. They found that there was increased sodium in the brain stem long before the rats showed any sign of having a migraine, according to the study published in the journal Pain.

"The importance of these findings is that they further emphasise the role of sodium increase early in migraines and help point to the region where migraine symptoms may be starting," said Michael Harrington director of neurosciences at Huntington Medical Research Institutes -- a California-based non-profit organisation.

Previous studies have showed that migraine sufferers have significantly higher sodium concentrations in their cerebrospinal fluid than people without the condition. Scientists have found that a number of different health scenarios seem to trigger migraines including anxiety, stress, exposure to light and hormonal changes.

According to the World Health Organisation, a large number of people with headache disorders are not diagnosed and treated - worldwide only 40 per cent of those with migraine are professionally diagnosed. Besides the painful headache, the condition is also disabling. In the Global Burden of Disease Study, migraine was ranked as the sixth highest cause worldwide of years lost due to disability.