Mmmm, a hot fudge sundae. The diet is supposed to start today, but surely it can wait until tomorrow -- or maybe the next day.
Many people know what's good for them and choose to do the exact opposite, especially when it comes to diet and exercise. Researchers are turning to the brain to find out what's behind this lack of self-control, a topic discussed in length at the American Association for the Advancement of Science meeting in Boston earlier this year.
In the future, there may be brain-based solutions to help you avoid that sundae; for now, researchers say, we can shape our environments to help us avoid temptation, and make firm commitments to change.
Value judgments and willpower
Pinpointing complex behaviors in the brain isn't simple; we weren't born with the words "impulsivity" and "willpower" etched into particular places on our heads. Scientists are still in the early stages of figuring out how billions of cells called neurons generate particular outcomes, and which circuits do what. But some clues have emerged from recent experiments.
When people who are trying to lose weight are confronted with meal choices, it appears there are two major factors in their decision: taste and health, said Todd Hare, assistant professor of neuroeconomics at the University of Zurich.
Hare's research shows that dieters who successfully turn down fatty temptations such as ice cream put more emphasis on the healthiness of food and relatively less emphasis on the taste.
It is the opposite for dieters who can't say "no" to sweets, he said. They say they're trying to eat healthy, but "they seem unable to shift away from the more automatic, stronger representation of taste," Hare said.
By using functional magnetic resonance imaging, or fMRI, scientists can see how a brain region called the ventral medial prefrontal cortex becomes active in valuing options in predicaments like this.
The ventral medial prefrontal cortex also appears to get involved in certain monetary decisions -- for instance, when researchers present participants with the choice of accepting a large reward later or a smaller reward immediately. Hare's research on this is not yet published, but the phenomenon was described in a 2011 research review.
Scientists have also located a second important brain area for these kinds of decisions: the dorsolateral prefrontal cortex. There is more activity in this region when participants choose options that appear better for them in the long run -- the healthy food item or the larger monetary reward that will arrive later.
The interaction between these two brain regions -- the ventral medial prefrontal cortex and the dorsolateral prefrontal cortex -- is stronger for people who show greater self control with either money or food, Hare said.
"They're working together to shape the way you're going to make your choices."
Scientists are also investigating brain areas associated with turning down temptations.
University of Cambridge neuroscientist Molly Crockett and her colleagues suggested in a study earlier this year that "precommitment" -- voluntarily restricting one's access to temptation -- is more effective at promoting self control than willpower.
In the experiment, men viewed erotic images that they rated according to personal preference. Then, in one task, they could decide in advance that they would not have the option to see the images they rated poorly. In exchange, they could see the higher-rated images after a greater time delay. This is called "precommitment."
In a different task, men were challenged to use willpower to actively resist viewing the lower-rated images while they waited for the higher-rated images. Precommitment appeared to be a better strategy on average.
In impulsive participants in particular, researchers saw more activation in the ventral striatum and ventromedial prefrontal cortex areas during precommitment. These relationships between brain activation patterns and impulsive tendencies suggest that people in general may have some self-awareness about their own self-control abilities.
Are self control problems, such as overeating and overspending, the result of poor willpower or impaired ability to precommit, or both? Further research on these issues could help the development of behavioral or pharmacological interventions, according to the study.
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