The scientists used functional magnetic resonance imaging, or fMRI, to image brain activity while subjects were faced with a hypothetical scenario: choose less money now, or more money later.
Boettiger recruited 24 subjects:19 provided fMRI data, 9 were recovering alcoholics in abstinence and 10 had no history of substance abuse. Another five were included in the genotyping analysis.
At the fMRI research facility at the University of California, Berkeley, financial decision tasks measured rational thinking and impulsivity. Sober alcoholics chose the now reward almost three times more often than the control group, reflecting more impulsive behavior.
While decisions were being made, the imaging detected activity in the posterior parietal cortex, the dorsal prefrontal cortex, the anterior temporal lobe and the orbital frontal cortex. People who sustain damage to the orbital frontal cortex generally suffer impaired judgment, manage money poorly and act impulsively, the scientists noted.
The study revealed reduced activity in the orbital frontal cortex in the brains of subjects who preferred now over later, most of whom had a history of alcoholism.
The orbital frontal cortex activity may be a neural equivalent of long-term consequences, Fields said.
Think of the orbital frontal cortex as the brakes, Boettiger explained. With the brakes on, people choose for the future. Without the brakes they choose for the short-term gain.
The dorsal prefrontal cortex and the parietal cortex often form cooperative circuits, and this study found that high activity in both is associated with a bias toward choosing immediate rewards.
The frontal and parietal cortexes are also involved in working memory being able to hold data in mind over a short delay. When asked to choose between $18 now or $20 in a month, the subjects had to calculate how much that $18 (or what it could buy now)
|Contact: Wallace Ravven|
University of California - San Francisco