A new study from the Washington University School of Medicine revealed that children suffering from clinical depression don't respond to rewards the same way as other children.

The study, published in the Journal of American Academy of Child and Adolescent, showed that decreased ability to enjoy activities and play could be a key sign of clinical depression in young children.

"These findings may show us how the brain processes emotions in young children with depression," said Joan L. Luby, MD, director of Washington University's Early Emotional Development Program and senior investigator of the study, in a press release. "The pleasure we derive from rewards -- such as toys and gifts -- motivates us to succeed and seek more rewards. Dampening the process early in development is a serious concern because it may carry over to how a person will approach rewarding tasks later in life."

For the study, the researchers asked 78 four to seven-old children to complete a simple computer game that involves choosing between two doors shown on the screen. Among the children, 53 have depression while the remaining 25 are psychiatrically healthy. In the simple guessing task, choosing the right door give points to the participants but choosing the wrong one will loss them points.

Using an electroencephalogram machine (EEG), the researchers measured the electrical activity in the brain of the children while they are playing the game. When the young children guessed the correct door enough times, they receive a toy that they were able to pick from a basket of figures, balls and plush items they had been shown before the computer session began.

The researchers observed that the brains of clinically depressed children have similar response as to those of non-depressive kids when they chose the wrong door and loss a point. However, EEG showed that the brain of children with depression did not react robustly when they chose the right door and won a reward.

With their findings, researchers advised parents to be consider loss interest in rewards such as toys and gifts as a sign that the child is suffering or prone to depression. Additionally, the researchers recommend seeking medical help if the child's condition persist.