This was the question that led to a study at the Michigan State University, where specialists experimented on 13 males playing a shooter game.

The subjects were playing “Tactical Ops: Assault on Terror” while their brains were monitored with an fMRI system. The results from 11 of the subjects revealed “large observed effects” characteristic of aggressive thoughts. The researchers said that this type of brain activity can be considered to be caused by virtual violence.

Functional Magnetic Resonance Imaging (or fMRI) describes the use of MRI (method of creating images of the inside of opaque organs in living organisms) to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of brain imaging.

“There is a causal link between playing the first-person shooting game in our experiment and brain-activity pattern that are considered as characteristic for aggressive cognitions and effects,” said Rene Weber, assistant professor of communication and telecommunication at MSU. “There is a neurological link, and there is a short-term causal relationship. Violent video games frequently have been criticized for enhancing aggressive reactions such as aggressive cognitions, aggressive effects or aggressive behavior. On a neurobiological level we have shown the link exists.”

The subjects were Germans aged from 18 to 26 years and they have played an average of 15 hours of video games a week. This study among others is a part of a larger movement around the world to place restrictions and to establish a clear regulation on the sale of violent video-games. Last week, Arnold Schwarzenegger, the California governor, signed a form of banning the sale of such video-games to children.