Design: Jen Sloan. Drink: Twobee/FreeDigitalPhotos.net. Weight: JKasawa/FreeDigitalPhotos.net. Scale: Toby Hudson

Whether it’s food, drugs, gambling, or an obsessive-compulsive act, each of us experiences temptation. For some people, it’s easy to stay strong most of the time. But for others, giving in to temptation is almost inevitable. What is it that separates those with self-discipline from those who end up mired in the trenches of addiction? To answer this question, researcher Jonathan Wallis of the Helen Wills Neuroscience Institute at UC Berkeley and colleagues looked to two regions of the prefrontal cortex, the anterior cingulate cortex (ACC) and the orbitofrontal cortex (OFC), which were previously shown to be linked with poor decision-making. To test the specific functions of these regions, the researchers measured which parts of the brains of macaque monkeys were active when the monkeys chose between pictures. The stakes of these decisions varied based on cost (number of lever pulls) and reward (amount of fruit juice). Wallis and colleagues found that the ACC was active during learning and expectation; in humans, it is thought to be the part of the brain that says “no” to alcohol in response to a bad hangover. However, these behavior-regulating signals were impaired in monkeys who repeatedly made unhealthy decisions despite past bad experiences. The researchers saw that the activity of the OFC changed in response to the importance of the scenario, while damage to the OFC affected the ability to distinguish between decisions of varying magnitudes. Next time you’re faced with an easy choice, thank your OFC—if every decision seemed as grave as what career to choose, proper decision-making would become confusing. “This is the first study to pin down the calculations made by these two specific parts of the brain that underlie healthy decision-making,” Wallis said. A better understanding of the underlying mechanisms of addiction may lead to deeper insight into the disease, and could point to molecular avenues for treatment.

This article is part of the Spring 2012 issue.