updated 8/13/2012 2:15:46 PM ET 2012-08-13T18:15:46

Researchers caution not to draw direct links between the violent themes of the Batman film and the shooting, but there is some evidence that people become densensitized to the effects of violence if they are exposed to these kind of images.

Police in Denver arrested James Holmes, 24, of Aurora, Colo., the man believed responsible for the shooting, which left 12 moviegoers dead and at least 38 injured.

One expert says that some people may think it could be okay to kill given the level of violent images that saturate our society.

"Will somebody like (the suspect) feel that its more acceptable, even in his own mind, to do this behavior because that person believes that society is more tolerant of aggressive behavior?" said Jordan Graffman, a neuropsychologist at the Kessler Foundation in West Orange, N.J., and expert in brain function. "Some people are simply delusional and will do it regardless of what society thinks. There's no 100 percent predictive relationship."

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Some observers are wondering about the film's content and whether it played a role in the suspect's motives, especially since the lead villain in the film and the shooter both were masked. The trailer for "The Dark Knight Rises" has been playing in heavy rotation on television for the past several weeks, and critics of the film have themselves been threatened with violence, according to The New Yorker.

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In 2010, while Graffman was at the National Institutes of Health, he and colleagues studied the effects of violent video games on a set of 22 boys between 14 and 17 years old. They found that violent images in games, television or movies could lead to a blunting of emotional responses and make subjects feel that violence is more acceptable.

"If you play these games a lot you will be less prone to have an emotional reaction," said Graffman, whose study was published in the journal Social Cognitive and Affective Neuroscience. "The reaction can make you upset. On the other hand, it's also a warning signal that something you are seeing is bad or frightening. That signal becomes diminished or immune to violent and aggressive behavior."

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Graffman said that more details are needed about the shooting in Denver to determine whether the suspect's state of mind was influenced by his habits, access to violent images, or perhaps his genetics.

Graffman said that some people carry a gene that -- combined with a history of family aggression or violence -- makes them more likely to commit violence themselves. There could be other biological causes as well. He noted that some parts of the brain that control violent behavior could be affected by a tumor growth.

That was found to be the case with Charles Whitman, the man who killed 16 people from University of Texas clock tower in 1966. The tumor wasn't found until his body was autopsied.

"It's complicated and there are no easy answers," Graffman said.

© 2012 Discovery Channel


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