Lead author Norman Farb, a doctoral psychology student, and colleagues at the University of Toronto showed 16 formerly depressed patients sad movie clips and tracked their brain activity using functional magnetic resonance imaging.
Sixteen months later, nine of the 16 patients had relapsed into depression and the researchers compared the brain activity of relapsing patients against those who remained healthy and against another group of people who had never been depressed.
"Part of what makes depression such a devastating disease is the high rate of relapse," Farb said in a statement.
"However, the fact that some patients are able to fully maintain their recovery suggests the possibility that different responses to the type of emotional challenges encountered in everyday life could reduce the chance of relapse."
The study, published in Biological Psychiatry, found faced with sadness, the relapsing patients showed more activity in a frontal region of the brain, known as the medial prefrontal gyrus.