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.
The scientists relied on M.R.I. scans of more than 100 adults, after establishing each subject’s personality type using a model known as the Big Five.
Any person, the model purports, can be described by their level of five traits: extraversion, agreeableness, conscientiousness, neuroticism, and openness/intellect.
Those that exhibit high conscientiousness are hard working and self-disciplined. They tend to have a larger-than-average lateral prefrontal cortex, enabling them to plan ahead, parse through complex thoughts and make decisions, the scientists found.
Neurotics, or those who often have negative, depressing thoughts, tend to have a smaller medial prefrontal cortex, a part of the brain known to regulate emotion.
Similarly, being agreeable corresponds to larger size in certain regions.
People who exhibited openness, a personality type that is creative and enjoys new ways of thinking, did not display noticeably different sizes in any regions.
It is important to remember that all such links between brain biology and personality are highly suggestive, and poorly understood. And although personalities are generally stable, they can be affected by experience over a lifetime, Dr. DeYoung said.
In other words, for those with a small medial prefrontal cortex, there is hope that it may grow.
By Sindya N. Bhanoo
June 28, 2010