I really loved the Brain Blitz presentations we did last week because they brought up a lot of questions I had never really thought of before. I was particularly struck by the question: How are personalities shown in and influenced in the brain?
There are many different ways we can evaluate and measure personality, and one is by examining where people put their attention and where they get their energy. C. G. Jung categorized this into two types, introversion and extroversion. Most psychologists believe that there is a spectrum between both categories in which most people fall into. People are more extraverted if the like to spend their time in the outer world of people and things, and more introverted if they like to spend their time in their own inner world of ideas and images.
Grodin and White (2015) investigated the parts of the brain that correspond with extraversion traits. They studied extraversion by dividing the personality dimension into two major types. “Agentic extroversion” is characterized by assertiveness, persistence, and achievement. People who are driven by the positive emotion of social warmth, friendliness, and affection, on the other hand, encompass “affiliative extroversion.” They used a personality questionnaire, structural magnetic resonance imaging, and voxel-based morphometry in attempt to find specific parts of the brain that correlate with these personality types.
Findings from this study indicated that extroverts (regardless of agentic or affiliative) have larger volumes of gray matter in the medial orbitofrontal cortex, regardless of age or gender. This area is believed to be associated with the upkeep of reward-guided decision making, goal-directed performance, and long-term social bonding. Grodin and White (2015) also found that male and female agentic extroverts, specifically, had a larger amount of gray matter left parahippocampal gyrus, left caudate, and left precentral gyrus. Males also showed increased volume in the right nucleus accumbens. The differences in parahippocampal gyrus are particularly interesting here, because this part of the brain is involved in learning and memory for reward.
I found these findings to be particularly interesting for a two reasons. Firstly, what could account for the gender differences between male and female brains? Is there something different about the functioning of the nucleus accumbens, allowing for this area to be larger in agentic extroverted males than agentic extroverted females? Secondly, these findings bring up a much larger question of “chicken-or-the-egg”/what came first. We know from brain plasticity that our behavior can, in fact, shape our brain. Are agentic extroverts naturally wired to feel more reward after social experiences than affiliative extroverts and introverts? Or, is this a part of the brain that has grown due to the agentic individual’s experience, resulting in a higher association between social experiences and reward?
Grodin, E., White, T. (2015). The neuroanatomical delineation of agentic and affiliative extraversion. Cognitive, Affective, & Behavioral Neuroscience. DOI: 10.3758/s13415-014-0331-6
The Myers-Briggs Foundation. Retrieved from http://www.myersbriggs.org/my-mbti-personality-type/mbti-basics/extraversion-or-introversion.htm.