Carl Schwartz of the Massachusetts General Hospital and his colleagues investigated a group of people in their early 20s who had participated in a previous study as two-year-olds. The young adults were first shown a variety of images of faces with neutral expressions. After this familiarization period, the subjects' brain activity was recorded using functional magnetic resonance imaging (fMRI) while the researchers showed them pictures of faces they had seen previously as well as images of novel faces. The scientists determined that the subjects who had been shy youngsters showed greater activity in an almond-shaped region of the brain known as the amygdala than did those who had been outgoing toddlers. Schwartz says the findings "show that the footprint of temperamental differences observed when people are younger persist and can be measured when they get older."
The researchers note that their sample size was small and suggest that further studies involving a much larger group will be necessary to clarify the link between brain differences and shyness. Because previous research has suggested that inhibited children may be at a greater risk of developing anxiety disorders than outgoing children are, insight into the biological basis of inhibition may help doctors improve diagnosis and treatment of these afflictions. Notes Schwartz, "It's only by understanding these developmental risk factors that one can really intervene in the lives of children early, to prevent suffering later in life."