Phrenologists thought the shape of the skull revealed insights into personality. Not so. But the shape of your brain? That's another story entirely.
A researcher from the University of Minnesota has found a link between the shape of different parts of people's brains and their personalities. Got a larger lateral prefrontal cortex? You're probably very conscientious, says Colin DeYoung, the lead researcher on the project.
DeYoung studied the five traits into which psychologists segment personality: conscientiousness, extroversion, neuroticism, agreeableness, and openness/intellect. Certain parts of the brain are known to be associated with behaviors connected to each trait. DeYoung had volunteers fill out a personality questionnaire, then used a brain imaging test to measure the relative size of different parts of the brain in light of those traits.
He found, for example, that conscientious people tend to have a bigger lateral prefrontal cortex, a region of the brain involved in planning and controlling behavior. The research appears in Psychological Science, a journal of the Association for Psychological Science.
But what he has found is merely a correlation, not evidence that size is caused by personality type. If you're extra happy, you won't grow a larger lobe, he says.
"The correlations we found can't prove that the brain systems identified are directly influencing personality," DeYoung told FoxNews.com. "It could be that an extroverted person has more experiences of a certain kind, which could influence the size of one part of the brain -- rather than that that part of the brain helps to drive extroversion."
Advances in genetics suggest parents-to-be may someday be able to genetically select for, say, blue eyes and brown hair. DeYoung is quick to point out that his work doesn't mean parents will be able to request an especially outgoing baby.
"It doesn't look likely that we will be able to select genetically for complex personality traits any time soon," he said. "The picture coming from genetic studies of personality is that individual traits are influenced by dozens and even hundreds of genes, each of which has only a very small effect. The path from genes to personality is so complex that it would be difficult to manipulate."
The study found associations for conscientiousness, which is associated with planning; neuroticism, a tendency to experience negative emotions that is associated with sensitivity to threat and punishment; and agreeableness, which relates to parts of the brain that allow us to understand each other's emotions, intentions and mental states. Only openness/intellect didn't associate clearly with any of the predicted brain structures.
"This starts to indicate that we can actually find the biological systems that are responsible for these patterns of complex behavior and experience -- what make people individuals," DeYoung said. He points out, though, that this doesn't mean that your personality is fixed from birth; the brain grows and changes as it grows. Experiences change the brain as it develops, and those changes in the brain can change personality.