The largest ever brain-scanning study on bipolar disorder has identified differences in the brain regions that control emotion and inhibition in people who have the condition.

Bipolar disorder affects up to three in 100 people and can be a debilitating condition to live with. The condition has been studied for decades but there have been very few conclusive findings about how it affects the structure of someone's brain. The disorder affects about 60 million people worldwide, according to data from the World Health Organization.

A landmark study has now found that the brain's grey matter – made up of the bodies of nerve cells – is thinner in several regions of the brains of people with bipolar. The difference is the greatest in the brain regions responsible for inhibition and motivation.

"We created the first global map of bipolar disorder and how it affects the brain, resolving years of uncertainty on how people's brains differ when they have this severe illness," said study author Ole Andreassen of the Norwegian Centre for Mental Disorders Research at the University of Oslo.

Bipolar patients who had a history of psychosis showed greater differences in grey matter than those who didn't. People who had had the condition for longer also showed greater differences in their grey matter.

The study also found one way in which lithium treatments for bipolar may be working. People who had taken lithium to treat the disorder had less thinning of their grey matter. Other treatments, including anti-psychotic and anti-epilepsy treatments, which are also often prescribed for bipolar, also seemed to have a protective effect on the brain of people with the condition.

"These are important clues as to where to look in the brain for therapeutic effects of these drugs," said Derrek Hibar of the University of Southern California, who was also a study author.

The researchers scanned the brains of 6,503 people using an MRI scanner, including 2,447 diagnosed with bipolar disorder. Previous smaller scale research has shown that some brain regions are affected by the disorder, but the findings have often been inconsistent. This MRI study, which is the largest ever on bipolar, is hoped to clear up some of the questions left by those studies.

"This new map of the bipolar brain gives us a roadmap of where to look for treatment effects," said Paul Thompson, also a study author and director of the ENIGMA consortium that ran the project.

"By bringing together psychiatrists worldwide, we now have a new source of power to discover treatments that improve patients' lives."

The research is published in a study in the journal Molecular Psychiatry.