Deciding between a risky financial investment and a safe one sets two parts of the brain into competition, say researchers in California.
As centres for pleasure and anxiety battle it out, a simple brain scan of the two can actually predict what a person will chose to do a few seconds before they do it: when joy beats worry in our brain, a risky decision is made.
Studies of how the mind handles risky behaviour have highlighted a number of neural hotspots. One is a peanut-sized region of the brain called the nucleus accumbens, which is loaded with the molecule dopamine and becomes active in anticipation of pleasure. The nucleus accumbens is known to play a role in the addictive effect of drugs.
Another region, known as the anterior insula, is stimulated in anticipation of a bad sensation. This area lights up in those predicting the onset of physical pain, and in generally anxious individuals.
Neuroscientist Brian Knutson of Stanford University and his colleague Camelia Kuhnen sought to compare how these two brain regions interact by asking 20 volunteers to play an investment game for a cash reward.
The participants pushed a computer button to select either a safe bond, which was guaranteed to earn them $1 in any given round, or one of two stocks. One stock had a 50% chance of earning the player $10 in a single round, and a 25% chance of losing him or her $10. The other carried a 50% chance of losing $10 and a 25% chance of winning it. But the scientists did not reveal which stock was which, making it an even riskier game to play.
As the participants completed the task, a machine took snapshots using functional magnetic resonance imaging, which revealed the active parts of the brain.
The results showed that the nucleus accumbens lit up about two seconds before a risky investment was made. When the anxious anterior insula was more active, the participants stuck to the safer choice.
The results of this study, which appear in the journal Neuron, reveal a previously unknown interplay between these two brain regions.
The thing to do is to work out when and why one part of our brain outdoes the other, says Martin Paulus of the University of California, San Diego, who has studied the role of the anterior insula in decision making. "The ultimate question is: when do you listen to one circuit and not the other?" he says.
The answer might help everyone from psychologists aiming to dull anxiety in nervous patients, to marketing gurus attempting to get customers to live dangerously.
(source: Nature News, August 31, 2005; http://www.nature.com/news/2005/050829/full/050829-12.html)