Brain regions battle for decision-making dominance

You're offered a giant bowl of rocky road ice cream on Thanksgiving, but you'd like to lose 15 pounds by New Year's Day. What do you do? Princeton University researchers have discovered that two separate brain areas are involved in the decision to choose short-term satisfaction or settle for long-term happiness.

These findings could be the first steps in understanding different types of impulsive behaviors, including acute addiction and attention deficit hyperactivity disorder, and could eventually lead to improvements in treatment, said lead author Samuel McClure, Ph.D., a neuroscientist and a postdoctoral fellow at Princeton's Center for the Study of Brain, Mind, and Behavior.

McClure and colleagues set out to answer a question that has long plagued economic theorists: Why do people sometimes make seemingly irrational decisions, choosing instant gratification over long-term goals? Until now, experts postulated a single decision-making process with a built-in inconsistency.

"Our study shows that there seem to be two separate brain systems involved in making intertemporal choices," McClure said.

Using functional MRI studies, researchers examined 14 volunteers who were asked to choose between gift certificates ranging from $5 to $40. Volunteers could choose the larger amounts if they waited for a longer time, between two to six weeks.

For all the decisions, regardless of whether the reward was delayed, fMRI registered equal activation in two brain regions associated with abstract thinking: the lateral prefrontal cortex and posterior parietal cortex.

When subjects chose longer term options, greater activity occurred in the frontoparietal region of the brain. Decisions for immediate gratification lit up parts of the limbic system associated with the midbrain dopamine system.

Although portions of the brain related to abstract thinking were activated during all decision-making processes, the limbic system, the portion most associated with emotions, won out over the abstract thinking regions when the reward was closer at hand, McClure said. The results were published in the October issue of Science.

While investigators now know that the limbic system is activated under conditions in which money is available immediately, and these areas of the brain are rich in dopaminergic innervation, they do not have evidence that directly links dopamine levels with their findings.

"We need to parse out how the limbic and lateral prefrontal systems interact in making intertemporal choices. Of particular importance is determining how this interaction works in determining individual choices," he said.

For more information from the online Diagnostic Imaging archives:

Eureka! fMRI maps insight

fMRI proves conquering pain can be mind over gray matter

fMRI knows your innermost secrets

Psychiatry calls on MRI to find origins of chronic conditions