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Study explores neuroscience of extroversion

Researchers examine possible link between personality, gray matter concentrations

An extrovert can be classified as one of two types: the “affiliative” people person who finds reward in connecting with others and the “agentic” high flyer who pursues social interactions in order to best advance his or her own goals. Differences between these two types may lie not just in personality but also deep within the skull, according to a study done by University researchers.

Published in the February issue of the journal Cognitive, Affective and Behavioral Neuroscience, the report examines the similarities and differences in neuroanatomy between the two extrovert personality types.

“We show that there may be a link between personality and brain anatomy,” said Erica Grodin GS, the lead author of the study. “People who score high on agentic extroversion have these increases in specific grey matter regions that the affiliative social extroverts don’t necessarily have.”

In order to separate participants into the two pools of extroverts, the researchers first had participants complete the Multidimensional Personality Questionnaire, a survey that asks questions about levels of sociability and assertiveness, Grodin said. The researchers then took “structural MRI scans of 83 men and women ranging in age from 18 to 54,” according to a University press release.

After the MRI, the researchers used “voxel-based morphometry,” a neuroimaging analysis technique that separates brain matter from cerebral spinal fluid, a brain component that was not necessary for the analysis, Grodin said. By combining the personality ratings with the anatomical data, the researchers compared volumetric differences in grey matter between the two groups.

As they had expected, they found that both types exhibit a greater-than-average volume of grey matter in the medial orbitofrontal cortex, an area involved in information processing and reward value, Grodin said.

Previous literature has shown the medial orbitofrontal cortex to be the “extroversion region,” Grodin said. But this study identified other areas of the brain that are associated with agentic, but not affiliative, extroversion.

Their results show that agentic extroverts boast more grey matter volume in the parahippocampal gyrus, the precentral gyrus, the nucleus accumbens and the caudate, according to the release.

“These regions are either involved in memory and reward or voluntary movement towards goal-directed action, so these are regions that will be activated when you’re trying to attain something,” Grodin said. “That’s a feature of agentic extroverts.”

“It was logical that these regions would be bigger as they both are involved in cognitive control, feedback-directed behavior and exploration,” said Joseph Austerweil, assistant professor of cognitive, linguistic and psychological sciences, who was not involved in the study. “As agentic extroverts are more assertive and confident, they’re more likely to go out and explore. That can lead to future connections with those brain regions,” he added.

But larger volumes in certain brain regions do not necessarily lead to distinct personality traits, as the study was purely correlational.

“Results are always sort of spun in the press releases so it sounds more causal than it is, since the more causal it sounds, the more sexy the results sound,” Austerweil said.

A longitudinal study may be necessary to more accurately study causation, Grodin said.

This study is a “good starting point” for future work on the relationship between personality and size of certain brain regions, Austerweil said, calling it a “nice” paper.

Though the results may be only correlational, the research provides “a way to help explain individual differences in personality,” Grodin said.


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