February 6, 2008

Aggression is as good as sex drugs and rock and roll

For the first time, researchers have confirmed that aggression and the powerful neurotransmitter dopamine are linked. Physorg has a review of the article detailing the basic procedures. I'll leave out the boring mess that interests me but if you want to check it out here is the source article found in the journal of Psychopharmacology (need journal rights to access).

One problem I have with the authors and the review article is they make baseless conclusions as to the how and why of this mechanism without any data supporting it. It may be true that the aggression complex in the mind is indefinitely linked with a powerful positive reinforcer through the action of dopamine but does this mean that all aggression elicits a euphoric response?

Dr. Kennedy, the PI on the project states:

"We learned from these experiments that an individual will intentionally seek out an aggressive encounter solely because they experience a rewarding sensation from it," Kennedy said. "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."
I have a real problem with this statement because it is a crux of Science: What is the data saying and what do I want my data to say? Dr. Kennedy may have fallen into this trap as most researchers have after making a breakthrough on previously undiscovered work. Is an aggressive encounter a rewarding sensation and is it motivating on its own? I would like to offer a counter point that the outcome of the aggressive encounter may offer more feedback than the action of aggression.

Take for example a male mouse placed in a cage and trained to press a button to expose a treat. Once this conditioning has been ingrained he is placed with a harem of females. The treat is replaced with a male mouse much larger than our subject and once the button is pushed the mice have a decision to make. Whether to tolerate the presence or confront each other. Invariably the first encounter will be a fight. During Kennedy's research the original male mouse would force the other mouse away from the group, but what happens if our subject mouse comes out the loser in the fight? How many times will he hit the button now? How long will he wait until hitting the button again? Will he intentionally hit the button to fight and lose again? These are all questions that can undermine Dr. Kennedy's statements.

Dr. Kennedy has no doubt shown that aggression (possibly coupled with the outcome) is definitely rewarding as his test subject continued to hit the button and confront his intruder and did so more frequently with time. After being exposed to dopamine blockers the action stopped, possibly indicating that without the reward function the aggression was no longer a motivating factor. But just how rewarding would it be if he lost the fight everytime?

This real world is full of examples of how aggression can be just like a drug in that to satisfy the urge the level of input has to rise, which is very clear now that dopamine has been linked to the motivation of aggresstion. Bullying seems to be a very good example of this correlating to the escalating quantity and mode of aggression the longer a child exhibits bullying behavior.

The role of dopamine in the aggression pathway does illuminate how important being aggressive was in our past. Dopamine is an extremely powerful neurotransmitter with the ability to shade the reality of people who are hooked on its effects (read: drug abusers) and also be a great motivator. This indicates that a strong positive reinforcement loop (most likely predicated on consequence) was needed early in human brain development. The keeping of a mate, warding off of outsiders, protecting young, and the fight for scarce resources or suitable living locations all require great amounts of aggressive intent for a single person.

In today's society these same elements are looked at as detrimental and outward aggression is very rarely socially positively reinforced (organized sport being an exception). This could create a problem within the mind as the biological framework rewards an action that the social nuclei of the brain most likely offers negative reinforcement for.

Cheers to Dr. Kennedy for his groundbreaking research and hopefully with time he can clarify this pathway of the brain to offer a better insight into the impetus and management of aggression.

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