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updated 4/6/2010 7:40:54 PM ET 2010-04-06T23:40:54

The brains of shy or introverted individuals might actually process the world differently than their more extroverted counterparts, a new study suggests.

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About 20 percent of people are born with a personality trait called sensory perception sensitivity that can manifest itself as the tendency to be inhibited, or even neuroticism. The trait can be seen in some children who are "slow to warm up" in a situation but eventually join in, need little punishment, cry easily, ask unusual questions or have especially deep thoughts, the study researchers say.

The new results show that these highly sensitive individuals also pay more attention to detail, and have more activity in certain regions of their brains when trying to process visual information than those who are not classified as highly sensitive.

The study was conducted by researchers at Stony Brook University in New York, and Southwest University and the Chinese Academy of Sciences, both in China. The results were published March 4 in the journal Social Cognitive and Affective Neuroscience.

Individuals with this highly sensitive trait prefer to take longer to make decisions, are more conscientious, need more time to themselves in order to reflect, and are more easily bored with small talk, research suggests.

Sensitive all around?
Previous work has also shown that compared with others those with a highly sensitive temperament are more bothered by noise and crowds, more affected by caffeine, and more easily startled. That is, the trait seems to confer sensitivity all around.

The researchers in the current study propose the simple sensory sensitivity to noise, pain, or caffeine is a side effect of an inborn preference to pay more attention to experiences.

They first used an established questionnaire to separate the sensitive from the non-sensitive participants. Then, the 16 participants compared a photograph of a visual scene with a preceding scene, indicating whether or not the scene had changed. Scenes differed in whether the changes were obvious or subtle, and in how quickly they were presented. Meanwhile, the researchers scanned each participant's brainwith functional magnetic resonance imaging.

Sensitive persons looked at the scenes with subtle differences for a longer time than did non-sensitive persons, and showed significantly greater activation in brain areas involved in associating visual input with other input to the brain and with visual attention. These brain areas are not simply used for vision itself, but for a deeper processing of input.

The sensitivity trait is found in over 100 other species, from fruit flies and fish to canines and primates, indicating this personality type could sometimes provide an evolutionary advantage.

Biologists are beginning to agree that within one species there can be two equally successful "personalities." The sensitive type, always a minority, chooses to observe longer before acting, as if doing their exploring with their brains rather than their limbs. The other type "boldly goes where no one has gone before," the scientists say.

The sensitive individual's strategy is not so advantageous when resources are plentiful or quick, aggressive action is required. But it comes in handy when danger is present, opportunities are similar and hard to choose between, or a clever approach is needed.

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