Knutson and collaborator Camelia Kuhnen (who received her PhD from the Stanford Graduate School of Business in 2006 and is now assistant professor of finance at Northwestern University) had already shown in a 2005 study using fMRI that brain activity could be used to predict whether people were about to take a financial risk. When they were, an area of the brain called the nucleus accumbens showed increased activation.
When they were about to choose to avoid the risk, a different area called the insula showed increased activation.
"We knew that we should be looking at [the nucleus accumbens] from the previous study. But what we didn't know is whether we could somehow control the activation in that area by presenting some completely irrelevant stimulus," Knutson said. "And whether that would change activation in that area and actually change behavior."
Knutson and his colleagues studied heterosexual male undergraduate college students. The images the men viewed were intended to stimulate an emotional response. Erotic images were used to elicit a positive response, snakes and spiders to prompt a negative response, and office supplies to trigger a neutral response.
In case any of the subjects found office supplies more repellent than snakes and spiders, the researchers had the men rate each image after the scans. They then derived personalized ratings from each of the participants, which were used to make sure that whatever brain activation they observed was properly correlated with the actual emotional response of the viewer.
After viewing each image, the participants immediately had to decide whether to take the high-risk option of gambling a dollar or the low-risk option of gambling a dime. Regardless of their choice, they had a 50-50 chance of winning or losing. Knutson and his colleagues gave each man $10 to gamble with prior to entering the MRI scanner. "We wanted them to care," Knutson said. Depending on the men's gambles and the random outcomes, they won or lost. "We took that money back if they lost it," he said.
What Were the Findings?
"What we saw is that when they viewed the erotic pictures, the activation in their nucleus accumbens increased compared to the other stimuli, and also that they had increased activation in that region before choosing the high-risk gamble," Knutson said.
The researchers then applied a statistical analysis to determine whether the activation in the nucleus accumbens accounted for some of the behavioral effect. "The answer was yes, at least in the case of the positive stimuli," Knutson said. "After people had seen those erotic pictures, they tended to pick the high-risk gamble more often, especially if they had been picking the low-risk gamble before.
"The interesting finding from an economic standpoint is that these completely irrelevant stimuli, these pictures that have nothing to do with the gambles or the history of outcomes that people have experienced with these gambles, still influence behavior," he said. "They seem to do so at least partially by influencing activation of these brain regions."
The findings have implications for what might make emotional appeals effective or ineffective in applications ranging from advertising to finance to politics and, perhaps not surprisingly, gambling.
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