Doctoral thesis sheds light on the neural basis of personality

[PRESS RELEASE, 11 February 2009] Introverted people have larger volumes in areas of their brain that are activated when thinking about other people, compared with extraverted people. This as well as other results are presented in a new doctoral thesis from Karolinska Institutet.

Are there differences in the brains of extraverted and introverted people? Is it possible through the measurement of basic properties of the brain to understand why one person is highly intelligent while another is neurotic? These are questions that Lea Forsman has examined in her doctoral thesis now being presented at Karolinska Institutet in Stockholm.

In one of the studies in the thesis, Lea Forsman has used magnetic resonance imaging to compare the brains of people who can be characterized as introverted or extraverted. The results showed that introverted people have larger brain volumes scattered throughout the brain.

"The volumes are especially large in regions of the brain that are known to be involved in the inhibition of behaviour and in areas that are known to be activated when we think about other people", says Lea Forsman. "This can reflect an introverted persons cautiousness. They ponder more over social situations before they act."

In another of the studies, levels of neuroticism, one of the Big Five personality traits, were determined in study participants. When these participants drummed a simple rhythm, it was seen that those who scored higher on the neuroticism scale had a harder time holding a steady pace over time. The differences in pace were too small to be noticed on a conscious level. According to Lea Forsman they can depend instead on basic differences in timing stability and precision in the brains activity.

"Neuroticism is often described as including forms of emotional and cognitive instability, but what is new here is that we have now shown that this instability can be seen in the simplest behaviour imaginable", says Lea Forsman. "Neuroticism is a risk factor for psychiatric conditions like depression and anxiety. Eventually this test could be used to help evaluate a persons risk for developing these illnesses."

Also the level of a persons intelligence was seen to affect results in the pace-holding test. The higher a participants intelligence, the better they were at holding a steady pace. However, while neurotic participants were more instable in tempo, lower intelligence was linked to small irregularities at the millisecond level between intervals.

"This suggests that intelligence and neuroticism are related in different ways to the brains temporal abilities that allow for precision and stability in its activity", says Lea Forsman.

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