Perhaps you've recently been diagnosed with depression. Maybe you've suffered occasional bouts of the blues. Anyone who has gone through it knows the added anxiety of having to "try on" different medications - taking one and then trying another when the first doesn't work, all the while living in the dark, empty hole in your chest.

There are blood tests to detect thyroid imbalances and sugar levels; if depression deals with brain chemistry, how come there isn't a standard diagnostic test? And what would that test look for?

A professor at Emory University, Dr. Helen Mayberg, published a study in JAMA Psychiatry, identifying a possible neuro-biomarker that could indicate the best way to treat a patient.

A random group of depressed patients underwent PET scans during the 12-week study while being treated with either the S.S.R.I. antidepressant Lexapro (escitalopram oxalate) or cognitive behavior therapy.

Mayberg found that 40 percent of study participants reacted to either treatment, but the brain scans of those who responded better to Lexapro showed differences compared to the scans of those who did well with therapy. Study participants with a high activity in a region of the brain called the anterior insula responded well to Lexapro, but not well to cognitive behavioral therapy. Those with low insula activity reacted positively to behavioral therapy, but did not respond well to the medication.

The anterior insula is a region of the brain entangled in "emotional self-awareness, cognitive control and decision making," according to The New York Times. Therapy may help those with an underactive insula by teaching the patient how to control their emotions. An overactive insula would need chemical help. Both approaches have similar effects, but different prime targets, and knowing how to use both types of treatment could change the way depression is handled by doctors.

Instead of endless trial-and-error prescriptions, doctors might now be able to better treat their depressed patients. Maybe one day, a brain scan could eliminate the guesswork of treatment and pinpoint exactly what each patient needs.