Clinically depressed people's performance in a 3-D video game suggests a part of their brain responsible for spatial memory does not function correctly, U.S. researchers have found.

Spatial memory tells the brain where objects are located and their orientation.

Scientists at the U.S. National Institute of Mental Health investigating the link between depression and the hippocampus — the centre of memory — found clinically depressed individuals asked to navigate a video game's 3-D virtual reality environment did poorly when compared to mentally healthy individuals.

The results of the study, led by NIMH researcher Neda Gould and published in the American Journal of Psychiatry, indicate the hippocampus does not work normally in a depressed person's brain.

Earlier studies have shown the hippocampus was smaller in depressed people than those without a mood disorder, and that depressed people have memory problems.

The new study, which looked at 30 depressed patients and 19 people without a mood disorder, found the 3-D game was a better way to measure the performance of test subjects than more traditional means.

The scientists had previously given the same people a two-dimensional memory test that is normally used in studies of this kind. They found that when they asked subjects to remember the location of objects on a computer screen, the two-dimensional test couldn't show the differences in spatial memory that were captured by the 3-D video game. 

Gould said the reason for this is likely that to play the 3-D game, people must use parts of their hippocampus that are not engaged by the two-dimensional test.

The results suggest the game is a superior tool to provide "a consistent, sensitive measure of cognitive deficits in patients with affective disorders," Gould wrote in the study.

The game they used was developed by scientists at the University College of London in England.