You many not realize this, but there are two types of people that fall under the extrovert personality category.

By very definition, an extrovert is someone that thrives under social stimulation, who focuses on the environment and people around him/her and is good at making quick decisions and multi-tasking.

However, there are two types of this specific kind of person. First, you have the "people persons," the affiliative, those people who feel rewarded when they can share with others. Then there are the "go-getters," the agentic, those who strive for achievement and leadership.

However, brain scans of these two groups of extroverts show that although both of these extroverted groups are similar, their brains have a few distinct differences.

Researchers chose 83 extroverted men and women as their test subjects, between the age of 18 to 54. Previous studies have focused mostly on seniors. They then screened volunteers for mental health, following that up with personality tests to determine which extrovert group they belonged to.

Once deemed mentally healthy and then categorized into a group, researchers took MRI scans of the test subjects and studied the volume of gray matter in different areas of the brain, including the medial orbitofrontal cortex, which helps the brain make choices when rewards are present.

"This is the first glimpse of a benchmark of what the healthy adult brain looks like with these traits," says Tara White, one of the study's authors.

All of the extroverts had high levels of gray matter in both their right and left medial orbitofrontal cortex, regardless of their age. However, researchers found that those who they identified as agentic extroverts had larger gray matter in other areas of their brains, too: particularly in the areas involved with learning for reward, planning towards reaching goals and receiving incentive-based rewards.

This perhaps explains why the agentic are the go-getters subset of extrovert: they are more goal-oriented and see the rewards that their goals can bring them.

Of course, this only shows that there's a link between the brain's gray matter and extroversion and doesn't explain exactly why this is the case. There's still many questions left unanswered: Are people born with larger areas of gray matter in these parts of the brain, making them extroverts upon birth? Or is it something that happens as they age and take on the extrovert personality traits?

"[The] findings provide a developmental benchmark from which to better understand the etiology of problems in agentic extroversion and affiliative extroversion, such as can occur in normal aging and neurodegenerative disease," writes study authors White and Erica Grodin.

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