Playing a violent video game can increase aggression, and when a player keeps thinking about the game, the potential for aggression can last for as long as 24 hours, according to a study in the current Social Psychological and Personality Science (published by SAGE).

Violent video game playing has long been known to increase aggression. This study, conducted by Brad Bushman of The Ohio State University and Bryan Gibson of Central Michigan University, shows that at least for men, ruminating about the game can increase the potency of the game's tendency to lead to aggression long after the game has been turned off.

The researchers randomly assigned college students to play one of six different video games for 20 minutes. Half the games were violent (e.g., Mortal Kombat) and half were not (e.g., Guitar Hero). To test if ruminating about the game would extend the games' effect, half of the players were told over "the next 24 hours, think about your play of the game, and try to identify ways your game play could improve when you play again."

Bushman and Gibson had the participants return the next day to test their aggressiveness. For men who didn't think about the game, the violent video game players tested no more aggressive than men who had played non-violent games. But the violent video game playing men who thought about the game in the interim were more aggressive than the other groups. The researchers also found that women who played the violent video games and thought about the games did not experience increased aggression 24 hours later.

This study is the first laboratory experiment to show that violent video games can stimulate aggression for an extended period of time. The authors noted that it is "reasonable to assume that our lab results will generalize to the 'real world.' Violent gamers usually play longer than 20 minutes, and probably ruminate about their game play in a habitual manner."