Some people are usually cheerful. Others are more likely to have sad, depressing thoughts. Such traits help make up our personalities.

But could such traits actually be related to measurable differences in brain structure?

In a new study in Psychological Science, neuroscientists report that extraverts tend to have a larger-than-average orbitofrontal cortex, a region that sits behind the eyes and is especially active when the brain registers rewards.

“They tend to be more cheerful and assertive and have a tendency to want awards,” said Colin G. DeYoung, the study’s lead author and a psychologist at the University of Minnesota. “It makes sense that they would have more of the machinery to keep track of winning.” The findings said nothing about how volume is linked to behavior, or which preceded which.