Many people have done a Meyers Briggs personality test (or something similar) to confirm whether they're one of two extremes: introvert or extrovert. The difference is basic: introverts need alone time to recharge their energies, while extroverts thrive and feel energized being around others. But of course there's more to these simplistic categories; there are two types of extroverts, for example, "affiliative" extroverts ie. "people persons," vs. "agentic" ie. ambitious leadership types who show personal agency. A new MRI study has shown that there are overlapping, yet unique distinctions within the brains of the two types of extroverts.
The study, called The neuroanatomical delineation of agentic and affiliative extraversion, published in the journal Cognitive, Affective, and Behavioural Neuroscience, used MR imaging to view the brains of 83 extroverted men and women aged 18-54.
All of the extroverts scanned showed high density in gray matter of the right and left cortex, but the agentic types had significantly higher density of gray matter in the brain regions associated with goal planning and receiving rewards as incentive. But, although researchers have distinguished brain differences among the two types of extroverts, they are unsure whether these differences occur by nurture or nature.
"[These] 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," concluded study author and assistant professor of  behavioural and social sciences at the Brown University School of Medicine, Tara White.