Published online: 8 December 2005;
| doi:10.1038/news051205-10
Heart rules head on risky calls
Uncertainty activates the brain's sentimental centres.
Roxanne Khamsi
When faced with uncertainty, people try to make the most logical decision, given the facts available. But a brain-imaging study has found that, when tackling these tricky decisions, the brain's emotional areas also spring into action.
Ming Hsu of the California Institute of Technology in Pasadena and his colleagues compared volunteers' brain activity in two betting games. As the volunteers played, the scientists watched changes in their brain activity using functional magnetic resonance imaging.
In one game, researchers gave volunteers the chance to guess the colour of a card drawn from a deck containing equal numbers of red and blue cards, and to bet on whether they were right.
In the other game, the ratio of red to blue cards remained unknown. Players in this game were less likely to put money on their guess. And there was a burst of activity in their brain's emotion-processing centres, the amygdala and the orbitofrontal cortex. The study is published in this week's Science1.
Playing it safe
The volunteers didn't know that the odds of them guessing right were actually the same in both games. Because players in the second game could only say 'red' or 'blue', their chances of betting correctly remained at 50%, whatever the ratio of blue and red cards.
That may sound odd: but as long as people are unbiased toward red or blue, they are equally likely to say either colour. And so even if the deck contains only red cards they still have a 50% chance of guessing correctly.
The scientists found that in the second game, the emotional parts of volunteers' brains typically sparked into life a few seconds before they made their choice - perhaps producing cautious feelings that swayed the subject against betting. The researchers believe their finding supports the idea that our brain wiring makes us averse to ambiguous risks.
Patients with a damaged orbitofrontal cortex bet the same regardless of whether they knew the risk or not. "A lot of these patients end up financially destitute," says Ming. He speculates that such people lack the emotional response to uncertainty, and the aversion to risk, of those with an intact orbitofrontal cortex.
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Aldo Rustichini, a decision-theory researcher at the University of Minnesota in Minneapolis, says that the findings nicely illustrate how emotion gets activated in tough situations. But he points out that the study found that risk also increased activity in analytical regions of the brain: "Decision-making involves both emotion and reasoning. The results in the paper point to both."
"It's important to try to understand how these two large networks we usually attribute to emotion and reason are interacting," Rustichini adds.
Ming and his fellow researchers intend to investigate whether indirect stimulation of the emotion-control centres can make a person more cautious. This could help to establish a causal link between amygdala activity and guarded decision-making, says Ming.
References
Hsu M., Bhatt M., Adolphs R., Tranel D., Camerer C., et al. Science, 310. 1680 - 83 Doi:10.1126/science.1115327 (2005).
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