Is Aggression Like Sex?

Jan. 15, 2008 — -- No wonder there's so much violence in the world. Scientists have found evidence that aggression rewards the brain in much the same way as sex, food and drugs.

Researchers at Vanderbilt University in Nashville found that the same "reward pathway" in the brain responds to aggression with the release of the neurotransmitter dopamine, known to be produced in response to various stimuli. Although the preliminary work involved lab mice, the scientists believe their findings probably apply to virtually all mammals, including humans.

"If I'm injected with cocaine, and I'm a mouse, my reward pathway activates. If I'm a human being and I'm injected with cocaine, that same reward pathway lights up," said Craig Kennedy, a professor of special education and pediatrics at Vanderbilt and co-author of a paper on the research, in the Jan. 14 issue of Psychopharmacology. Now, Kennedy and a colleague, Maria Couppis, have shown that the same reward pathway is involved in aggression as well.

The pair came up with a new way to test the theory that aggression feeds upon itself by stimulating the reward system.

The volunteers for the research included lab mice, a male and a female, called the "home mice," in one cage, and a bunch of other mice, all males, in another cage. The female was removed from the home cage, and a male intruder was allowed in. There followed an intense battle between the two males, with lots of tail rattling, boxing and biting.

After a few minutes of combat, the intruder was removed, and here's where the interesting part comes in. The male home mouse had been taught to "nose poke," a trigger to communicate that he wanted another piece of the intruder.

That action allowed the intruder to return, and another battle ensued, and so on into the evening.

But that, in itself, proves nothing, other than a mouse likes a little action now and then. However, the researchers came up with a technique to insert a tiny tube into the small area of the mouse's brain where the reward pathway is found. That allowed them to pump in a drug that suppresses dopamine in that small area of the brain.