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How you react to stress influences how easily you resist or succumb to disease, including viruses like HIV, discovered UCLA AIDS Institute scientists. 

Reported in the Dec.15 edition of Biological Psychiatry, the new findings identify the immune mechanism that makes shy people more susceptible to infection than outgoing people.

"Since ancient Greece, physicians have noticed that persons with a 'melancholic temperament' are more vulnerable to viral infections," said Steve Cole, principal investigator and assistant professor of hematology-oncology at the David Geffen School of Medicine and a member of the UCLA AIDS Institute.

"Our study pinpoints the biological mechanism that connects personality and disease."

The UCLA team studied the effect of stress on viral replication in a group of 54 HIV-infected men. All of the men were still in the early stages of the disease and in good health. ...

The researchers put each man through a series of stress tests in the lab to measure the response of their autonomic nervous system. 

First, the scientists monitored the subject's response to a tiny stimulus, such as an unexpected beeping sound. ....

"Shy persons didn't adapt to the beeps as fast as other people," Cole said. "Their heightened nervous system response indicated that the sound was more irritating to them."

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The biggest difference is that extroverts deal almost exclusively with a world outside themselves while introverts take the world within to process it. 

If that sounds a little mysterious, the best way to tell in a heartbeat is that extroverts get energy interacting with other people and with the stimuli in the environment (noise, lights, motion) while introverts get very drained by this. ...

Explain to your friends and family that you're an introvert. They may not know what this means and a little educating goes a long way. ...

It's time to stop apologizing for yourself and your legitimate needs and interests. Introverts like Warren Buffett, Michael Jordan and Steven Spielberg made it to the top by being exactly who they are and you can too.

The brains of shy people overreact when they see strange new faces, which may explain personality differences and also offer ways to treat anxiety disorders, U.S. researchers said on Thursday. 

Even people who have seemingly overcome their innate shyness have an extra-strong reaction in the amygdala, the emotional center of the brain, when shown a new face, the researchers found.

People who had been judged as toddlers to be inhibited showed in the scans that the amygdala structure in their brains responded much more actively to unexpected sights than did those subjects who had been judged as children to be more outgoing, said Jerome Kagan, a researcher in the department of psychology at Harvard University.

"That is support for the notion that the reason they were shy, timid and reserved when they were 2 years old is because they had an excitable amygdala," said Kagan. 

This suggests that shyness is a temperament that can be inherited, but the researcher said this temperament does not necessarily determine one's eventual personality.

"They are now 22 years old," Kagan said of the test subjects. "A lot of the ones who were fearful aren't fearful anymore. They have overcome it. But the question is, did they still have a very active amygdala."

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Tests were conducted on 13 people who had been evaluated as shy as 2-year-olds. The results were compared tests on nine people who had been evaluated as children to be outgoing and bold.

"We had assumed, but never measured, that ... the shy, inhibited group had inherited a certain chemistry" in the amygdala, Kagan said. ....

Although some children are shy and others are outgoing, he said, these traits can change with time and life experiences. "People overcome their shyness," Kagan said. "You can also acquire shyness."

He understood that introversion and extroversion are on a continuum. 

At one end are introverts. They feel depleted by too much external stimulation and are energized by internal sources (ideas, impressions, thoughts). 

Extroverts, at the other end of the continuum, are energized by external sources (activities, socializing, things) and lose energy during down time.

Some people use both sides of the continuum almost equally. We all possess both ways of increasing and decreasing energy but most of us inherently require more introverting or extroverting to accumulate our energy resources.

That's such a metaphor for how she exists in the world: She keeps banging into things, and doesn't know why she keeps bruising herself. She meets Oscar, who's got no skin on his emotions and no skin on his bones - Ralph [Fiennes] lost quite a lot of weight for the part: he was a stick insect. 

Really isolated people don't develop skin the same way that people who are more socialized do.