Snidman, 1991a). Inhibited children are controlled and gentle. When they
throw a ball or knock over a tower of blocks, they do so in a manner that is
“monitored, restrained, almost soft. ”Inhibited children are the ones who cling
to their mothers or fathers when entering a new playroom or when meeting
new children. They are slow to explore new toys or equipment and may go
for several minutes without saying a word.
Uninhibited children show the opposite pattern. Approximately 25% of the
children in the researchers ’samples fall into this category (Kagan & Snidman,
1991a). These children jump right in to play with a new toy or to climb on a
new piece of playground equipment. They usually start talking soon after they
enter a new play area, even if they don ’t already know the other children
playing there.
On the surface, the difference between the two kinds of children appears
to be their level of anxiety. But inhibited children are not simply more afraidof everything. Rather, they are vulnerable to a specific form of anxiety psy-
chologists refer to as anxiety to novelty . These children are cautious about
and at times fearful of new people and new situations. Inhibited toddlers of-
ten turn away from strangers and bury their face in mother ’s or father ’s leg.
As adults, they may express their discomfort in a new situation by withdraw-
ing socially and waiting for others to speak first.
Researchers find evidence from a number of sources that these inhibited
and uninhibited styles represent inherited biological temperaments. Inhibitedand uninhibited children show a number of physical differences almost from
the moment of birth (Fox, Henderson, Rubin, Calkins, & Schmidt, 2001;
Moehler, Kagan, Brunner, Wiebel, Kaufmann, & Resch, 2006; Rosenberg &
Kagan, 1989). They differ in terms of body build, susceptibility to allergies,
and even eye color (inhibited children are more likely to have blue eyes).
Inhibited children are more likely than uninhibited children to show signs of ir-
ritability, sleep disturbances, and chronic constipation during the first fewmonths of life. Newborns later identified as inhibited children respond to unfa-
miliar stimuli with increased heart rate and pupil dilation (LaGasse, Gruber, &
Lipsitt, 1989).
Additional evidence for a biological foundation comes from research with
older children and adults. In particular, neuroimaging studies find inhibited anduninhibited children ’s brains react differently to events and images (Bar-Haim
et al., 2009). In one investigation, 10- to 12-year-old boys and girls classi-
fied as inhibited reacted to noises with different brain stem responses than
did uninhibited children (Woodward et al., 2001). Other investigators findinhibited children have an abnormally high amygdala response when pre-
sented highly novel or uncertain stimuli (Perez-Edgar et al., 2007; Schwartz,
Wright, Shin, Kagan, & Rauch, 2003).
Of course, how inhibited children express their anxiety changes as they
mature. Nonetheless, researchers find evidence for a fear of the unfamiliarthroughout childhood and into adulthood (Gest, 1997; Kagan & Snidman,2004; Moehler et al., 2008). Trained judges in one study looked at motor
activity —arm and leg movements, tongue protrusions, crying —in 4-month-old
infants to place the children into inhibited and uninhibited categories (Kagan,
1989; Kagan & Snidman, 1991a, 1991b). The psychologists observed theTemperament 233