Our brains are wired for pleasure. So if you are finding it hard to live up to your New Year's resolution to give up certain foods or drinks, blame it on your brain.

When we see — or merely think of — something we have experienced as a reward, our brain flushes with dopamine — even if we aren’t particularly paying attention. “We don't have complete control over what we pay attention to,” the senior author of a recent study, Susan M. Courtney, said in a statement. “We don't realize our past experience biases our attention to certain things.”

“What we tend to look at, think about and pay attention to is whatever we've done in the past that was rewarded,” she added.

“Our past experience biases our attention to certain things.”

Johns Hopkins University researchers asked participants to find red and green objects on a computer screen filled with different colored objects. Participants got $1.50 for finding red objects and 25 cents for finding green ones.

The next day the same participants were asked to find certain shapes on the screen while PET scans were conducted. There was no reward, and color no longer mattered. Even so, every time a red object appeared, people focused on it. At the same time the part of their brain involved in attention was flooded with dopamine, a brain chemical released when we receive rewards.

Participants found the shapes they were looking for, but it took longer because the previously rewarded “red” distracted them.

The finding helps explain why dieting and breaking addictions are so hard to do. People are biased toward rewarding stimuli. In this case, they were not getting a reward and weren't expecting one, but the stimulus — red — was still triggering a release of dopamine. It had become part of their reward system.

Not everyone was equally distracted by the previously rewarded red. The most distracted were those who had the most elevated dopamine levels. Those who were better able to focus on the task at hand appeared to have suppressed any release of dopamine.

Distractions tend to be bigger for people prone to addiction and smaller for people who find abstaining easier or who are depressed and do not care about rewards, said Courtney.

The findings suggest that in the future, a drug targeting these neurochemical distractions could be developed to help dieters, addicts and others trying to overcome problem behaviors.

The study is published in Current Biology.