Even small children show big differences in personality. For example, some are adventurous and social, while others are shy and reclusive. According to a 2003 study in the journal Science, these differences in temperament may be related to differences in brain structure.


The roots of shyness in the brain. I'm Bob Hirshon and this is Science Update.

Are you socially inhibited? Withdrawn? Uncomfortable in new situations? Well, according to a recent study led by Carl Schwartz of Harvard Medical School, you might have a shy brain.

The researchers took brain scans of young adults who had been especially shy at the age of two. When shown pictures of unfamiliar faces, these people had a very strong response in an area of the brain called the amygdala.


It's a crucial switch point and control center for the processing of information related to things out there in the environment that might require more evaluation, whether it is potentially threatening or whether it is simply different.

That suggests that their brains are highly sensitive to new things. And that sensitivity may have contributed to their shy childhood dispositions.

Dr. Schwartz says it's not yet clear if shy kids consistently become shy adults. But he notes that few of his subjects had major social phobias.


One of the most inhibited kids in the entire study, when he called on the phone, he was warm, he was related, he sounded comfortable, he was studying mathematics at Berkeley.

He says the study could help psychologists better understand the development of personality. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Over the past decade, scientists have discovered many biological and genetic factors that seem related to human personality and behavior. This is a good example. It's important to understand not only what studies like these suggest, but also what they leave unanswered.

First of all, a little more background on this report. The subjects were people who had been participating in a scientific study for pretty much their entire lives. They are ordinary people leading ordinary lives, except that every so often, starting from age two, they have reported to Harvard for a battery of psychological tests. Schwartz became involved in the studies when the subjects were young teenagers; today they're adults.

This kind of study is called a "longitudinal study," and it's used to track everything from the progression of medical conditions to social trends over a long period of time. These studies take literally decades to complete. Often, they report findings at several points along the way, and compare them to past reports.

When the subjects first entered the study at age two, they were tested for a number of personality differences. One test separated the children into two basic groups: novelty-seekers, who loved to handle new objects, explore new places, and interact with their environment, and inhibiteds, who were shy and preferred the comfort of the familiar. Later, at age 13, the inhibiteds were three times as likely as the novelty-seekers to have social anxiety disorders (a form of extreme shyness that calls for psychological treatment). Still, the majority of the inhibiteds did not have anxiety disorders. So was their childhood shyness "just a phase," or was it hard-wired into their brains?

Schwartz's experiment suggests the latter. At age 21, people who were inhibited as toddlers have different responses in their brain. That is they have more activity in their amygdalas in response to new stimuli. The amygdala is an ancient part of the brain that seems to be a kind of switchboard: as the world is processed through our senses, the amygdala appears to flag new or unusual information (like loud noises or sudden movement) and send it on to higher parts of the brain for more processing.

It follows that people with more active amygdalas might be more sensitive to new information, and that in turn could make them shy. The fact that people with more active amygdalas were also shy as children certainly supports this idea. But remember, the study shows only a correlation. It's not clear that the brain differences actually cause differences in shyness, or the other way around. It's likely that shyness is due to a combination of biological and environmental influences. The more we know about each separate piece of the puzzle, like this one, the better scientists will be able to put it all together in the future.

Now try and answer these questions:

  1. What is the primary finding of Schwartz's study?
  2. What is a longitudinal study? How does the brain scan experiment make use of longitudinal data?
  3. What is the difference between causation and correlation? How does it relate to this study?
  4. What additional evidence (from humans or animals) might lend support to the hypothesis that a sensitive amygdala contributes to shy behavior? Describe an experiment in which you would test this hypothesis.

For Educators

Fear, from Psycheducation.org, is a related article that looks at the amygdala's role in the feeling of fear.

Shyness, from TeensHealth, provides an overview of shyness and a look at the benefits and drawbacks of being shy.

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