oungsters who play endless computer games could be stunting their brain development and risk becoming more violent, say scientists.
According to a new study, teenagers who play such games only use parts of the brain linked to vision and movement. This, in turn, means other parts of their brains are left underdeveloped - which may lead to violent behaviour.
By contrast teenagers who carry out simple arithmetic exercises also use the part of the brain most associated with learning and self control.
Evidence already shows that computer games are linked to aggression. But it was previously thought that the violence was a psychological result of playing computer games, rather than biological.
In the latest study Professor Ryuta Kawashima from Tohoku University in Japan found that the frontal lobe of the brain plays an important role in learning - and in turn works hard at keeping behaviour in check. This, he says, could explain why small children often do things they shouldn't - because their brains are undeveloped.
He found that activities such as arithmetic thicken certain fibres connecting neurons in the brain which in turn strengthen learning and behaviour patterns. As a result, he concluded that the more the brain is stimulated, the more fibres are thickened - and the greater ability a child has to learn and control behaviour.
Students involved in the research were given small doses of a radioactive drug - like a dye - which allowed a scanner to map out a colourful image of their brains at work. The more activity that took place in the brain the redder the image.
The results showed there was a much higher level of brain activity during arithmetic compared with when watching computer games - particularly in the areas of the brain associated with learning.
Professor Kawashima has also shown that arithmetic stimulates greater brain activity in children than listening to music or reading. In particular, reading out loud can help stimulate activity in the frontal lobe.