Depression is one of the most common mental disorders in the United States, and in addition to reducing a person's quality of life, depression can seriously impact other aspects of health.

Yet treatment is often hit-or-miss with some antidepressants not working at all and others taking months to ease symptoms. However, a study published in the journal Brain found that a functional MRI brain scan may help predict which patients will respond to antidepressants.

Researchers at the University of Illinois at Chicago and the University of Michigan performed fMRI scans on patients with major depression who were to begin antidepressant therapy. They found that patients who showed more communication between two networks in the brain — the error detection network and the interference processing network — when they made a mistake while performing a cognitive task, were less likely to respond to antidepressant medication.

The error detection network activates when someone notices they've made a mistake, and the interference processing network activates when deciding what information to focus on.

"We believe that increased cross-talk within these networks may reflect a propensity to ruminate on negative occurrences, such as a mistake, or a deficit in emotional regulation when faced with a mistake, and our medications may be less effective in helping these types of patients," says study author Natania Crane.

The study results could be an important step in treating depression. Finding the right therapy can take months. Drugs used to treat major depressive disorder take eight to 12 weeks to have a noticeable impact on mood and other symptoms, and patients may not respond to the first drug prescribed or suffer side-effects, requiring a switch in medications.

Researchers studied 36 adult patients with major depressive disorder who were not being treated with drugs. Subjects had fMRI scans and took surveys regarding their depressive symptoms. They were then assigned one of two antidepressants: escitalopram (Effexor, a selective serotonin re-uptake inhibitor, 22 participants) or duloxetine (Cymbalta, a serotonin-norepinepherine re-uptake inhibitor, 14 participants).

During the fMRI scan, participants were instructed to press a button every time they saw the letters X, Y and Z flash across a screen, but not to press the button a second time if a letter was repeated.

The patients were followed up during and after 10 weeks of antidepressant therapy. They completed surveys and interviews to determine if their medication was easing their symptoms.

Those whose brains had a stronger reaction when they made a mistake were less likely to respond to antidepressants.

"Using our model, we were able to predict with a very high degree of accuracy — in fact 90 percent — which patients would respond well to antidepressant treatment, and which would not," said University of Illinois at Chicago professor Scott Langenecker.

The researchers also found that participants who made more errors during the cognitive task were more likely to respond to antidepressant treatment.

"This is an important step toward individualized medicine for depression treatment," said Langenecker. "Using cognitive tests and fMRI, we can identify who will respond best to antidepressant therapy and who may need other effective therapies that work through different mechanisms, like psychotherapy."

Every year, major depression affects about 14.8 million Americans. It can have an extremely negative impact on a patient's health. For instance, depressed people are four times as likely to have a heart attack and have a significant increase risk of dying, and of having a second heart attack when compared to those who don't suffer from depression.

Researchers at the Harvard School of Public Health, Boston, analyzed 28 studies that included a total of 317,540 participants who were followed from two to 29 years. They found that depression was linked with a 45 percent increased risk for stroke, a 55 percent increased risk for fatal stroke, and a 25 percent increased risk for ischemic stroke.