In a social situation, it's easy to tell the difference between a wallflower and the life of the party, but a new study suggests we can also spot differences in their brains.
The results show the size of certain brain regions is related to people's personalities. For instance, highly altruistic people had a bigger posterior cingulated cortex, a brain region thought to be involved in the understanding of others' beliefs. Bigger regions are assumed to be more powerful. [Top 10 Mysteries of the Mind]
"One of the things that this shows is we can start to develop theories about how personality is produced by the brain," said study researcher Colin DeYoung, of the University of Minnesota.
While people's personalities are likely shaped by both genetic and environmental factors, the findings might help explain the differences in people's actions and demeanors from moment to moment, he said, or "what produces the patterns of behavior and emotion and thought that we describe as personality."
The big five
There are many ways to describe someone's character — from talkative to anxious to hardworking and organized. Psychologists have found that many traits often go together and have grouped these traits into five overarching categories — extraversion, neuroticism, agreeableness, conscientiousness and openness/intellect.
Psychologists can get a pretty good picture of someone's personality by determining to what degree they express each of these traits. [Read: Personality Set For Life By 1st Grade]
Scientists have only recently begun to link up personality research with neuroscience to try to figure out the underlying brain mechanisms responsible for personality differences.
DeYoung and his colleagues imaged the brains of 116 participants who had previously completed a questionnaire designed to assess their personality in terms of the "big five."
Next, they matched up all the brain images. Since everyone's brain is different, the images won't line up perfectly right off the bat. So the researchers picked one image — from a participant who scored about average for all five traits — to serve as a "reference brain."
A computer program was then used to squish and stretch the images so that they all lined up with the reference brain. This allowed the researchers to compare all the subjects' brains, and see how large or small certain brain regions were relative to one another.
Personality in the brain
A connection between brain region size and personality was found for four out of the five traits (all except openness/intellect).
Those who scored high on neuroticism — which indicates a tendency to experience negative emotions, including anxiety and self-consciousness — was associated with a larger mid-cingulate cortex, a region thought to be involved in the detection of errors and response to emotional and physical pain. Neurotics also had a smaller dorsomedial prefrontal cortex, a region implicated in the regulation of emotions. [Read: Why Neurotics Haven't Died Out]
Extroverts, those who are sociable, outgoing and assertive, had a larger medial orbitofrontal cortex, a region involved in processing rewards. This goes along with the idea that extroverts are sensitive to rewards, which in our society often involve social interactions and status.
Conscientious people, who tend to be orderly, industrious and self-disciplined, had a larger middle frontal gyrus, a region involved in memory and planning.
The researchers note however, that a bigger brain region does not necessarily mean the region has better functioning, although extensive evidence supports this assumption.
The results do not indicate, that people are doomed to embody one personality or another for their whole lives. Though it's not necessarily easy, personalities can, and do change.
"Our experience can change the brain," DeYoung said. "And as the brain changes, personality can change," he said.
The results were published online April 30 in the journal Psychological Science.