Choosing a treatment for depression is not always easy. People respond to drug treatments and psychotherapies in different ways, making it hard to determine whether therapy or medication will work best for someone. Now researchers have found that a new method, which involves scanning the brain, that may help simplify the process.

“Currently, finding the right antidepressant treatment is a trial-and-error process because we don’t have precise tests,” said Leanne Williams, one of the authors of the new study. “For some people this process can take years. As a result, depression is now the leading cause of disability.”

Researchers found they could predict who would respond to antidepressants, and who wouldn’t, with 80% accuracy.

Williams and her team scanned the brains of 80 people with depression. They were particularly interested in how the amygdala — the area that is thought to govern both emotion and anxiety — responded to pictures of happy or fearful faces.

In addition to the scans, people in the study filled out questionnaires about their childhoods, including early life stressors, like abuse and neglect, family problems, illness, death and natural disasters. Each was given either sertraline (Zoloft), escitalopram (Lexapro) or venlafaxine (Effexor), and followed to see how they responded to these drugs over a period of eight weeks.

Those people who had been exposed to childhood trauma and those whose amygdalas responded to happy faces were likely to be helped by antidepressant; but those whose amygdalas didn’t show a response to happy faces were less likely to be helped. The researchers were also able to predict who would respond well to antidepressants, and who wouldn’t, with 80% accuracy.

“We were able to show how we can use an understanding of the whole person — their experiences and their brain function and the interaction between the two — to help tailor treatment choices,” Williams said. “We can now predict who is likely to recover on antidepressants in a way that takes into account their life history.”

What’s likely happening is that the amygdala has become over-sensitive to negative stimuli over time, a process that started in childhood. When there’s trauma in childhood, the amygdala becomes hyper-sensitive to both negative and positive stimuli, since children with trauma often need to be hyper-attuned to the grownups around them.

But over time, some people who experience trauma may lose their response to positive stimuli, and are left with amygdalas that are only sensitive to negative stimuli. These people, the team says, are not as likely to be helped by an antidepressant, so it may be best for them to start with a different form of treatment.

“For those patients who have lost this capacity, putting them down an antidepressant path is likely to cause more heartache,” Williams said. “That’s when you would consider other types of treatment. First, treat the effects of the childhood trauma through methods such as trauma-informed psychotherapy, and then consider antidepressants.”

It might also save a lot of time and money to use this method, since, as the authors point out, depression has become the leading cause of disability worldwide, and a huge cause of lost work and wages.

And perhaps the best argument is that for any other health issue, medical scans are routine, before jumping into a treatment. “If we are thinking about trying to get this right the first time,” says Williams, “it’s useful to consider the option of ordering a scan. It’s already done for so many other things — a broken leg, a heart problem, a potential tumor.” Why not depression as well?

The study is published in Proceedings of the National Academies of Science.