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 cortex 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) would be worth in a month and then compare it to $20 and decide whether it would be worth the wait.
The parietal cortex and the dorsal prefrontal cortex were much more active in people unwilling to wait. This could mean, Boettiger said, that the area is working less efficiently in those people.
The COMT gene has two common variants with a single amino acid difference at position 158; valine (Val) or methionine. The Val form of the gene is associated with lower dopamine levels, and Boettiger's study showed that people with two copies of the Val allele (resulting in the lowest dopamine levels) had significantly higher frontal and parietal activity and chose now over later significantly more often.
"We have a lot to learn," Boettiger said. But the data take a significant step toward being able to identify subtypes of alcoholics, which could help tailor treatments, and may people who are at risk for developing addictions and provide earlier intervention.
The bigger picture, Boettiger said, is that her study provides more evidence that addiction is a disease, something even some of her peers do not yet believe.
"It's not unlike chronic diseases, such as diabetes," she said. "There are underlying genetic and other biological factors, but the disease is triggered by the choices people ma
|Contact: Clinton Colmenares|
University of North Carolina at Chapel Hill