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.