Psychologists who study the infinite variety of humans’ personalities and temperaments often find themselves drawn to biological explanations of the personality traits that make us who we are. They surmise that factors such as heredity or brain structure must play key roles in whether we are outgoing or introverted, easygoing or prone to worry, callous or caring.
But take that line of reasoning too far, and you get dangerously close to phrenology, a kind of science-cum-parlor game that was all the rage during much of the 19th century. The idea behind phrenology was that each of the mind’s faculties lies at an exact and predictable spot in the brain, and that a person’s propensities could be divined simply by observing the size and shape of his or her skull, which was thought to reflect the size and shape of the underlying faculties.
This, of course, required complex maps of the head and specialists — readers, if you will — to guide the curious in discovery of themselves or others. It all looked very scientific — and in some ways, helped give rise to the field we now know as neuroscience.
But what if there was a germ of truth to the idea that personality traits do basically reside in predictable regions of the brain, and that the size or shape of those regions do reflect the fundamental makeup of a person’s character? That is the intriguing preliminary finding of a study published this week in the journal Psychological Science. And it is the basis for a fledgling discipline called “personality neuroscience.”
The “big five” personality traits — extraversion, neuroticism, agreeableness, conscientiousness and openness or intellect — are the dimensions of character that psychologists seem to agree make up each person’s unique personality “fingerprint.” Guided by neuroscience findings suggesting specific roles for certain brain regions, a team of researchers led by University of Minnesota psychologist Colin DeYoung measured the size of several regions in 116 healthy subjects’ brains. They also had the subjects fill out standardized personality inventories, allowing them to locate each subject on the continuum of each of the “big five” traits.
For all but one of the “big five” — openness, or intellect — the researchers found that specific brain structures did vary in size in ways that tracked closely with a subject’s score on one of the “big five” traits. If a subject scored highly on, say agreeableness, she was more likely to show greater heft in her brain’s posterior cingulate cortex, which becomes active when a person exercises empathy. An extrovert was more likely to have a brawnier medial orbitofrontal cortex, a region known to be involved in responding to social reward.
Unlike the phrenologists of the 19th century, DeYoung’s team doesn’t presume to know whether differences in the size of a brain region give rise to unique personality characteristics, or whether our personality differences cause our brains to develop in unique ways — say, that when we practice random acts of kindness, our “agreeableness” center grows larger, or that a lifetime of social isolation might cause a region associated with “extraversion” to shrink.
