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Your Brain's Got Tasty Treats on Its Mind

A new study shows the brain's learning mechanisms make distractions like snack foods—or drugs—harder to avoid.
A graphic highlighting the brain's reward circuit. (Photo: NIH Image Gallery/Flickr)

A graphic highlighting the brain's reward circuit. (Photo: NIH Image Gallery/Flickr)

Why do we have a hard time avoiding sugary snacks when we're on a diet? And why do we get distracted by our phones all the time? According to a new experiment, both answers might be a direct consequence of the way our brains learn about choices and their rewards—and the difficulty our brains have in forgetting them.

One issue of great practical importance in psychology is how we develop habits, and how we can break the bad ones. For example, how do we get in the habit of eating poorly, and how can we learn to eat better? One aspect of those questions is how much control we have over what we pay attention to. For example, eating better is going to be a lot easier if we're not constantly distracted by sugary cakes.

Our brains might be set up precisely so they do get distracted.

Unfortunately, Brian Anderson, Susan Courtney, and their colleagues argue, our brains might be set up precisely so they do get distracted. To investigate that possibility, they first trained a group of 20 people to associate a color—green, for example—with a higher cash reward using a simple learning task. Specifically, participants had to search a screen for a green or red circle for a cash reward. If the circle was green, say, the reward was $1.25 on average; for red circles it averaged 50 cents. (For half the participants, that scheme was reversed, but the point is the same: People learned to associate one color with more money, and another color with less.)

The next day, participants returned to complete a similar task, except this time color no longer mattered. Instead, subjects searched the computer screen for different shapes, and there were no cash rewards involved. However, on some tests there was a green circle present on the screen. The question is, could that green circle, like the sight of a tasty cinnamon roll during a boring staff meeting, distract people from the task at hand?

It could—and it did. On trials with a green (that is, high-value) distractor, participants took longer to find designated shapes compared to when there was no distractor. Tests using positron emission topography brain scans to track dopamine, a chemical closely related to the experience of rewards and pleasure that is released in different parts of the brain, backed up the idea that people are distracted by the prospects of a reward. As expected, more dopamine was released when the green circle appeared, even though it was irrelevant to the task at hand and participants had no reason to expect any rewards as a result of its appearance.

What that means, the researchers point out, is that distraction isn't a matter of willpower or anything relatively easy to overcome—it's inherent to the way our brains learn about the world, albeit to different extents in different people. The results could help researchers better understand and perhaps treat eating disorders, drug addiction, and other ailments, the team writes.


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