Gonna watch the NFL conference championship games on Sunday?  You’ll see evidence for a new finding: aggression is rewarding. In what scientists from Vanderbilt University say is the first study of its kind, they report that aggressive behavior triggers dopamine, a neurotransmitter in the brain that is known to be part of a reward system. Dopamine levels increase when people and animals get food, sex, and drugs like cocaine.

The researchers report in the online edition of the journal Psychopharmacology that when a caged male mouse was faced with an intrusive male mouse that replaced a female previously in the cage, the first male got aggressive. He bit and boxed the interloper. But when the intruder was removed, the mouse would engage in behavior the he learned would bring his target back.  The researchers think that aggression was its own reward.
 
More evidence: when the mouse that was deprived of his female companion got a drug that inactivated dopamine receptors, he brought the intruder back less frequently.  So remember that when Michael Strahan is smashing into Brett Favre, he really, really likes it.

—Steve Mirsky, with reporting by Harvey Black