If extroverts needed another reason to talk about their behavior, a study identifying two types of extroverts gives them the perfect opportunity. Although only one type-agenic extroverts-may seek to capitalize on the information.
Brown University researchers Erica Grodin and Tara White discovered what they are calling the first-ever correlation between individuals with the self-identified behaviors of affiliative and agenic extroversion and more development in certain regions of the brain.
Agenic extroversion indicates sensitivity to reward, ability to identify and move toward achieving goals, persistence, and a desire to seize leadership. In common parlance: a go-getter. Affiliative extroversion comprises traits that are probably closer to most people's definition of an extrovert: social warmth, drawing meaning from close social relationships, and deriving joy from engagement with others. In short-a people person.
The study, which appeared in the journal Cognitive, Affective, and Behavioral Neuroscience, noted several similarities in neuroanatomy even after accounting for age differences among the subjects.
Using structural MRI scans of 83 men and women ranging in age from 18 to 54, the researchers found that both types of extroverts showed greater volume in the medial orbitofrontal cortex, one of the least understood regions of the human brain. Among the traits attributed to the orbitofrontal cortex are the adaptive learning presumed to be present when one is comparing the expected reward or punishment with the actual experience of reward or punishment.
It's also been associated with decision making, behavior evaluation, expectations of social reprisal, and suppressing negative emotions when, for example, playing a game of chicken (wherein one is required to quickly evaluate risk-reward).
White told New York Magazine that one of the significant components of the study is that people reliably self-report in terms of their emotional experiences of the world. Often in such studies, the self-reporting feature raises questions about validity because of the many inconsistencies in people's experience of being human. In this case, White noted, when people tell you about their experience of the world, it's reflected in their own mapped neural core.
The reward seekers-agenic extroverts-also demonstrated enhanced development in the left parahippocampal gyrus, left caudate, left cingulate gyrus, and left precentral gyrus. These regions are involved in learning about and memory for being rewarded, cognitive behavior control, and the planning and execution of voluntary movement toward a goal.
In addition, men in the study had greater volume in the right nucleus accumbens, which is involved in identifying rewards and the incentives toward attaining them.
There were no specific markers beyond the orbitofrontal cortex for affiliative extroverts-the people persons.
Grodin and White cautioned that the results of the study show simply an association between the behaviors and the neurology, and that no explanation is yet available as to why the neural regions in some people are larger or whether the traits are inborn or acquired.
The study utilized a neuroimaging technique known as voxel-based morphometry, or VBM, which registers each brain in the study to a template in order to account for anatomical variance from subject to subject. VBM analysis was specifically responsible for identifying several of the higher gray matter volumes. The technique was previously used in a somewhat famous study showing larger volumes in the hippocampi of London taxi cab drivers (http://www.scientificamerican.com/article/london-taxi-memory/).
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