Scinetists reveal why introverts prefer being alone

In a new study, scientists found that the brains of introverts don't pay much attention to human faces, a reason why they prefer to remain alone while their socially outgoing counterparts love the company of others.

In fact, introverts' brains didn't seem to distinguish between inanimate objects and human faces, said researcher from the Salk Institute for Biological Sciences in La Jolla, California. The findings, they said, adds weight to idea that underlying neural differences in people's brains contribute to their personality.

"This is just one more piece of evidence to support the assertion that personality is not merely a psychology concept," study author Inna Fishman was quoted as saying by LiveScience.

"There's some broader foundation for the behaviour that you see ... implicating that there are neural bases for different personality types." For their research, Fishman and her Salk Institute colleagues recruited 28 participants, aged 18 to 40. They ranged in personality from introverted to somewhat extroverted to very extroverted.

Electrodes placed on the subjects' scalps recorded the electrical activity in their brains, a technique known as electroencephalography (EEG), to study a particular change in the brain's electrical activity known as P300.

The change, which shows up as a deflection on a person's EEG, can be elicited by certain tasks or by a change in the environment, such as when the room is very quiet and you all of a sudden hear a loud nose. According to the researchers, the brains' reaction occurs within 300 milliseconds, before the person is aware of the change. To evoke P300, Fishman used a method known as the "oddball task" in which subjects saw a series of male faces and every so often a female face appeared. They were also shown pictures of purple flowers interspersed with pictures of yellow ones.

The higher subjects had scored on a test for extroversion, the greater their P300 response was to human faces, suggesting that extroverts pay more attention to human faces.

There was no link between scores on extroversion and the P300 response to flowers. But, introverts had very similar P300 responses to both human faces and to flowers.  "They just didn't place a larger weight on social stimuli than they did on any other stimuli, of which flowers are one example," Fishman said.

"This supports the claim that introverts, or their brains, might be indifferent to people -- they can take them or leave them, so to speak. The introvert's brain treats interactions with people the same way it treats encounters with other, non-human information, such as inanimate objects for example," Fishman said. The results strongly suggest that human faces, or people in general, hold more significance for extroverts, or are more meaningful for them, she said.

The study was presented recently at the Annual Convention of the American Psychological Association.