Toronto, Aug 8 (IANS): Is your teenaged son addicted to playing action video games? Beware, it can reduce episodic memory and spatial navigation, and increase the risk of developing brain disorders such as depression, schizophrenia, Alzheimer's and Parkinson's disease, researchers have warned.

The findings showed that habitual players of action video games had reduction in grey matter in the hippocampus -- a key brain area for memory.

This challenged the previously held notion that it may boost brain power, reduce stress and aid in improving symptoms of depression, the researchers said.

"Video games have been shown to benefit certain cognitive systems in the brain, mainly related to visual attention and short-term memory," said lead author Greg West, associate professor at Universite de Montreal (UdeM) in Canada.

Further, the study showed that instead of the hippocampus, 85 per cent of players tend to increasingly make use of another part of the brain called the striatum to navigate their way through a game.

Striatum has an area known as the caudate nucleus that acts as a kind of "autopilot" and "reward system" and also helps us form habits and remember how to do things like ride a bicycle.

However, the more the players use the caudate nucleus, the less they use the hippocampus, and as a result the hippocampus loses cells and atrophies, the researchers rued, in the paper detailed in the journal Molecular Psychiatry.

"If action video games lead to decreases in grey matter in the hippocampus (of young adults), caution should be exerted when encouraging their use... (by) children, young adults and older adults to promote cognitive skills such as visual short-term memory and visual attention," West suggested. 

According to the study, patients with Parkinson's disease combined with dementia, as well as those with Alzheimer's disease, schizophrenia, depression or PTSD -- all of whom have less grey matter in their hippocampus -- should "not be advised to (follow) action video game treatments."