Shy Temperament: More than Just Fearful
Compared to others, children with extremely shy temperament have heightened brain activity in response to any prominent event, whether the event is positive or negative, a new imaging study suggests. This kind of temperament — "behavioral inhibition" — early in life is a risk factor for subsequent development of mental disorders. The study also shows that temperamental and physiological differences found in these children persist later into childhood and adolescence, raising the possibility that the differences may be markers of risk for mental disorders as youth develop. The study results suggest that differences in temperament are reflections of stable, long-lasting, physiological differences in some brain mechanisms.
The findings were reported by NIMH investigator Monique Ernst, M.D., Ph.D., and colleagues in the June 14, 2006, issue of The Journal of Neuroscience.
Previous studies of children with behavioral inhibition detected heightened activity in a fear-processing area of the brain called the amygdala in response to events perceived as threatening, as might be expected in people who are shy. This study instead examined response to a rewarding event, and showed that the brain again over-reacted, although in a different area (the striatum) than when it responded to negative events. The striatum is involved in cognitive processes, including learning, memory, and thinking, and in processing of both positive and negative events. The new findings add to a growing map of potential links between functions of brain areas, behaviors, and risk of mental disorders.
The 32 adolescents in this fMRI study had been monitored since infancy for temperamental characteristics. Thirteen of the children had been found to have behavioral inhibition at an early age; 19 had not and were included in this study for comparison. The average age of the participants at the time of the current study was 13. The study examined responses to a cue with positive emotional implications (monetary gains). fMRI showed more activity in the striata of adolescents with behavioral inhibition, compared to the other adolescents, whether the incentive was to gain cash or to avoid losing it.
Behavioral inhibition is different from the occasional shyness seen in most children. Behaviorally inhibited children are more fearful than others and have a more severe, constant type of shyness. They also have differences in baseline levels of the stress hormone cortisol, heart rate, and electroencephalogram (brainwave read-out), compared with children who don't have it. They have difficulty adapting to social situations; are over-vigilant and hesitant in nature; and tend to react strongly to new experiences.
Guyer AE, Nelson EE, Perez-Edgar K, Hardin MG, Roberson-Nay R, Monk CS, Bjork JM, Henderson HA, Pine DS, Fox NA, Ernst M. Striatal Functional Alteration in Adolescents Characterized by Early Childhood Behavioral Inhibition, Journal of Neuroscience, 26(24):6399-6405. June 14, 2006.