Temperamental differences in children's responses to change can be identified early and are quite stable over time. These "sensitive" (or in psych lingo, behaviorally inhibited) children are likely to withdraw or be shy in novel or uncertain situations. fMRI studies do show significant differences in the brain responses of these children - its the amygdala that's sensitive or reactive to changes.
In the figure above, "sensitive" adolescents had much more reactive amygdalas looking at happy or fearful faces than "non-sensitive" or regular controls. The irony about all this is that children who seem poor at social skills often find themselves lumped together - although some are too sensitive to the emotions of others, while others are oblivious or under-sensitive. One also might add that findings such as this suggest that the term behavioral inhibited is almost a misnomer - its not that these kids are withdrawing because of apathy or blunted responeses. Just the opposite - they are very emotionally responsive than their peers - and that accounts for their overload in social situations.
BTW temperament is forgotten all too often when a child is having problems behavioral problems at home or at school. The best book we've seen in a long time that provides practical advice for parents and teachers is Barbara Probst's When the Labels Don't Fit. This book covers topics such as intensity and inflexibility, sensitivity, overload, "electronic addiction", impaired time perception, and differences in learning or perceptual style.
Attention Alters Neural Responses to Evocative Faces in Behaviorally Inhibited Adolescents
Temperament in the Classroom