The Vanderbilt study, appearing in the January edition of Pharmacology, is
the first to reveal a link between behavior and the activity of dopamine
receptors in reaction to an aggressive episode. “We learned from these
experiments that an individual will intentionally seek out an aggressive
encounter solely because they experience a rewarding sensation from it,” said
Craig Kennedy, professor of special education and pediatrics at Vanderbilt.
“This shows for the first time that aggression, on its own, is motivating, and
that the well-known positive reinforcer dopamine plays a critical role.”
For the experiments, a pair of mice – one
guy, one gal – was kept in a cage and five “intruder” mice were stationed in a
separate cage. The female mouse was temporarily removed, and an intruder mouse
was introduced in her place, a switcheroo that triggered an aggressive response
from the “home” male mouse. The bullying behavior included all the usual schoolyard
antics: tail rattle, an aggressive sideways stance, boxing, and biting.
But it’s one thing to lash out at an unwelcome burglar; quite another to throw
down the gauntlet and demand a rematch. In the Vanderbilt study, the home mouse
was trained to poke a target with its nose to get the intruder to return, at
which point it inevitably sought a rumble. The trigger was presented once a
day, and the home mouse consistently prodded it, indicating the aggressive
encounter was viewed not as a threat but as a reward.
When treated with drugs that suppressed their dopamine receptors, the mice looked to fight
less frequently, even though they were observed to be no less lethargic in their overall movements. “It’s well known that dopamine is produced in response
to rewarding stimuli such as food, sex, and drugs of abuse,” said Maria
Couppis, who conducted the study as her doctoral thesis. “What we have now
found is that it also serves as positive reinforcement for aggression.”
No word on whether any of the mice actually TALKED about Fight Club …
