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By Jennifer Welsh, LiveScience

What gives you the motivation to go the extra mile for a promotion or a perfect test score? It may be your levels of a brain chemical called dopamine. Researchers have found amounts of this chemical in three brain regions determine if a person is a go-getter or a procrastinator.

Dopamine does different things in different areas of the brain. So while high levels in some brain regions were associated with a high work ethic, a spike in another brain region seemed indicate just the opposite - a person more likely to slack off, even if it meant smaller monetary rewards.

"To our surprise, we also found a different region of the brain, the anterior insula, that showed a strong negative relationship between dopamine level and willingness to work hard," study researcher Michael Treadway, graduate student at Vanderbilt University, told LiveScience.

The fact that dopamine can have opposing effects on different parts of the brain puts a wrench in how psychotropic drugs that affect dopamine levels are used for the treatment of attention-deficit disorder (ADD), depression and schizophrenia, Treadway noted. The general assumption has been that these dopamine-releasing drugs have the same effect throughout the brain.

The researchers scanned the brains of 25 young adult volunteers and put them through a test to see how hard they were willing to work for a monetary reward. They would choose either an easy or a difficult button-pushing task, and get rewarded either $1 or a variablevalue of up to $4. They repeated these 30-second tasks for 20 minutes.

Some of the participants opted to work harder for the larger reward by completing thedifficult task, while others chose the easier task more often and accepted the small reward. Does this choice make them lazy? Maybe, Treadway said: "They were less motivated by this particular task. We suspect it predicts, to a certain extent, how motivated they might be in other contexts."

They compared testing data with brain scans of these patients, with and without administration of the dopamine-releasing drug amphetamine, which provides a reading of how much dopamine is normally released in different areas in the brain. [Inside the Brain: A Journey Through Time]

"You've got someone deciding, 'Do I want to work a bit more or a bit less? How do I factor in these odds?' Some people just went for it," Treadway said. The researchers found that these hardworking people had the most dopamine in two areas of the brain known to play an important role in reward and motivation, and low dopamine levels in the anterior insula, a region linked to motivation and risk perception.

These differences may mean that the choice between working hard and slacking off depend on how the brain weighs risk and reward, the researchers said. Some people are more wary about taking a risk and expending extra energy for an unlikely, but larger, reward. Other people concentrate more on the big reward they could get, and downplay the possible losses (of energy and time).

These findings could be important in getting a better grip on mental illnesses characterized by a lack of motivation, such as ADD, depression and schizophrenia, the researchers said. "Understanding some of these region-specific patterns may help us, at some point down the line, do a better job of predicting how patients may respond to different types of medication,"

"We think that part of what is going on in depression is some alteration in motivation pathways and part of the impetus for this study was working towards a model to be able to test the role of motivation in depression," Treadway said. "This may be a way to assess the motivational side of depression."

The study was published today (May 1) in the Journal of Neuroscience.

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