Researchers have now found that violent shooter games including Call of Duty, Halo, Medal of Honor and many more, have shown an increase in brain activity of arousal and decrease of brain activity in the areas of attention and self-control.
Vince Matthews and a group of his researchers did a study on teens using two video games. One which was violent (Medal of Honor), the other game which wasn't (Need for Speed). They made two groups each with 22 teens in it and let one group play the violent game and the other group the non-violent game. Right after the kids were done playing they were given a MRI. The results were that there was a negative effect on brain areas of the teens that played the violent "Medal of Honor" video game compared to those whose played the non-violent "Need for Speed" video game.
It is unknown if playing the violent game has a permanent effect on the brain, but it has shown that violent games do cause increased brain activity in arousal. But it is shown that correlation does not equal causation.
I do believe that violent video games cause arousal in the brain compared to other non- violent video games, but it doesn't mean that people can blame the video game industry for teen violence in the real world. A lot of times for kids that are to young to play these violent video games they are allowed by their parents to play them.