Modern media such as TV and computer games are changing our minds, and the more we are exposed to them the greater the changes.

They are making us smarter and better at some tasks, but worse at others. And there is no getting away from the fact that on-screen violence fosters off-screen violence.

Brain imaging and other physiological measures also reveal changes in emotional responses to violent images as a result of viewing violence or playing violent games. Bruce Bartholow of the University of Missouri, Columbia has found that people with a history of game playing have a reduced brain response to shocking pictures, suggesting that people begin to see such imagery as more normal. Another study found that frontal lobe activity was reduced in youngsters who played a violent video game for 30 minutes, compared with those playing an equally exciting but non-violent game. This brain region is important for concentration and impulse control, among other things. A region called the amygdala, important for emotional control, was more aroused in those who experienced the violent game.

Other studies show that children store memories of violent media acts in brain regions reserved for long-term storage of significant events. These memories can pop back into the mind very rapidly, even when not wanted, as flashbacks.

The effects fall into three categories. There’s a kind of imitation effect, where we seem to learn by example how to behave in certain situations. There’s desensitisation, which means we become less shocked by and more tolerant of violence. Finally, there is the “mean world” effect, where people feel more vulnerable after seeing images of bad situations.