New York, Dec 17 (IANS): Brains of children who are clinically depressed react less robustly to success and rewards as compared to other children who are not depressed.

The study showed that when a child, as young as four years old, does not seem to be excited by rewards, such as toys and gifts, it may be a sign that the child is depressed or prone to depression.

Decreased ability to enjoy activities and play, remain persistently sad, irritable or less motivated, who feel excessively guilty about wrongdoing and those who experience changes in sleep and appetite also may be at risk.

"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," said Joan L. Luby, Director of Washington University School of Medicine in St. Louis, US.

For the research, the team involved 84 children aged between three and seven, who played a computer game that involved choosing between two doors shown on the screen.

The electrical activity in their brains were measured using an electroencephalogram machine (EEG).

While the brains of clinically depressed children responded similarly to those of non-depressed children when points were lost, the response when the correct door was chosen was blunted.

The EEG results showed that their brains did not react as robustly from the pleasurable event of choosing the correct door on the screen.

"The study may show us how the brain processes emotions in young children with depression," Luby said.

The study was published in the Journal of the American Academy of Child and Adolescent Psychiatry.