Phrenology was the intellectual rage of 19th century America. Edgar Allan Poe and Walt Whitman each incorporated bits of the popular personality theory into his works, and Herman Melville went so far as to make his most famous narrator, Ishmael, an amateur phrenologist. The essayist Ralph Waldo Emerson was obsessed with the practice, alternating between enthusiasm and fear about phrenology’s deterministic view of the brain and behavior.
For those who need a quick refresher, phrenology was the theory that an individual’s personality could be “read” from the shape of his skull. The bumps and depressions in the cranium were thought to represent the shape of the brain below, which itself was determined by the volume of the 27 discrete “brain organs.” These brain modules presumably housed such personality traits as cleverness, pride, wit, and affection.
Phrenology is considered pseudoscience today, but it was actually a vast improvement over that era’s prevailing views of personality. For example, phrenology for the first time recognized the brain as the “organ of the mind,” although phrenologists lacked the sophisticated tools of modern neuroscience and could only speculate on the details. Unfortunately, they got the details laughably wrong.
But phrenology may be undergoing a redemption of sorts. Not the skull part—that’s still considered bunk. But neuroscientists today are using their new tools to revisit and explore the idea that different personality traits are localized in different brain regions. The emerging field of personality neuroscience is producing some intriguing early results.
Two of the leaders in this new field are psychologists Colin DeYoung of the University of Minnesota and Jeremy Gray of Yale, who have been using a brain scanner to search for evidence of the so-called “big five” personality traits. There is growing scientific consensus that every human personality is a unique mix of just five core attributes: extraversion, neuroticism, agreeableness, openness/intellect, and conscientiousness. Every other character trait is subsumed under one of the big five—or its flip side.
These traits can be reliably measured using personality inventories, which DeYoung and Gray ran on more than a hundred volunteers in a recent study. Basic brain research has in recent years revealed a great deal about the purposes and functions of various brain regions, and the scientists drew upon these insights. They wanted to see if volunteers’ dominant personality traits matched up—in a way that makes sense—with the size (and presumably the power) of these clusters of neurons.
Take extraversion, for example. Extraversion includes qualities like assertiveness and sociability and talkativeness—all traits having to do with positive emotions and rewarding social experiences. Based on this, the scientists guessed that the most extraverted people would have larger than normal brain regions associated with sensitivity to reward. And when they used a MRI to measure the volume of the extraverted subjects’ brains, that is exactly what they found. As reported on-line in the journal Psychological Science, the regions known to be involved in the reward experience were noticeably larger.
Similarly, the scientists found that neuroticism—a tendency toward negative emotions like irritability and anxiety—was associated with the brain regions involved in threat and punishment. Agreeableness—a catchall for altruism, empathy, cooperation and compassion—correlated with regions known to process those traits. And, finally, the most conscientious volunteers had unusually large brain structures involved in “executive” powers like future planning and following complex rules. In short, the brain studies lent strong support to the idea that the big five personality traits have a biological foundation. Indeed, the only trait of the five that was not significantly linked to a particular region was openness/intellect, which is an umbrella for imagination and aesthetics and intelligence. Even here, there was some suggestive evidence linking this trait to the brain’s center for working memory and attention and reasoning.
Personality traits are reliable predictors of everything from health and well-being to career and relationship success. The most conscientious people, for instance, tend to be the healthiest, and to excel at school and work. So finding the biological roots of these individual differences would be an important advance. But having neurological roots does not mean that character is unchanging. That deterministic notion of the brain and personality has gone the way of phrenologists’ bumpy heads.
Excerpts from “We’re Only Human” appear regularly in The Huffington Post and Scientific American Mind. Wray Herbert’s book, On Second Thought: Outsmarting Your Mind’s Hard-Wired Habits, will be published by Crown in September.