Between a touchy temperament in infancy and disorders in adulthood lie two highly significant things: Parents.

Babies may be born with a propensity to overexcitability in response to stimulation, but it's practices that determine whether such infants become fearful of unfamiliar people and events later in . In a picture now emerging of the psychobiology of anxiety, researchers and clinicians of various stripes are discovering how early experience and inheritance interact to shape behavior for life.

While innate infant reactivity contributes powerfully to later anxiety disorders, the development of anxiety is scarcely inevitable.

"Parents' actions affect the probability of anxiety disorder in the child," report Harvard psychologists Jerome Kagan, Ph.D., and Doreen Arcus, Ph.D., who have studied hundreds of infants and followed them for up to five years so far. Arcus told an annual meeting of the American Association in Philadelphia that among parents who impose limits on their children's behavior, none of the overexcitable infants wound up fearful at age two.

By contrast, at that age, over 40 percent of highly reactive infants typically are behaviorally inhibited, displaying avoidance, ceasing activity, crying, and generally showing distress in the face of unfamiliar people, objects, and events.

Indeed, psychiatrist Michael Liebowitz, M.D., reported at the same symposium on fears and inhibitions that "overprotectiveness brings out the worst in kids." As head of Columbia University's unit on panic disorders, he finds that an unusually high proportion of panic patients report having had overprotective parenting in childhood.

True, behaviorally inhibited kids experience stress in situations most others find un-threatening. But shielding them from events is hardly the solution.

"All the parents [in our study] are middle-class and loving," Kagan points out. "Among them, two philosophies are represented. One is, 'I have a sensitive child that I must protect from stress.' So this parent, finding the child playing in the kitchen trash, tends not to set limits with a firm 'Don't do that,' but distracts the child. As a result, the child does not get the opportunity to extinguish the response."

The other, more authoritative--not authoritarian-- views discipline as , and requires the child to adjust to the world. This parent has few qualms about saying "No. No trash," and lifting the toddler's hand from the trash before distracting him. "It's a subtle difference--but a profound one," says Arcus.

Still, "teaching children how to cope with the experience of stress is important," Arcus and Liebowitz agree. Parents who allow their children to deal with life's day-to-day troubles help them develop more resiliency and better coping strategies. "Overprotective parents actualize the tendency to anxiety disorder."

TEMPERAMENTAL JOURNEY

o Approximately 20 percent of white infants are born with the high reactivity pattern that gives rise to the inhibited temperament.

o White babies are generally more reactive than Asian babies.

o Inhibited kids have narrower faces than uninhibited ones. It's known from animal studies that stress in utero inhibit the lateral growth of the upper jaw bone.

o Temperamental patterns of infants can be detected in utero by heart rate measurement.

o Early infant reactivity reflects inherited excitability levels of nerve cells in the amygdala.

o Inhibited kids show higher rates of than do noninhibited kids (33 vs. 10 percent).

o Parents of children with behavioral inhibition have significantly higher rates of , , and general childhood and adult anxiety disorders.