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There are other ways to confirm disorders. Egger has conducted experiments in which preschoolers diagnosed with anxiety conditions are shown either positive images (like a picture of three smiling girls) or threatening images (like a snarling dog). An eye-tracking system follows their gaze. As a rule, anxious kids focus longer on the parts of the pictures that signal danger such as the dog's teeth and eyes. They even look longer at the girls' faces, in an apparent attempt to see if any less obvious threat lurks. "There appears to be a dysregulation of the fear circuit," says Egger. "This creates a bias in attention to threat, real or not."
What causes a child to become anxious or depressed is seldom clear. Genes do play a role, particularly in depression and obsessive-compulsive disorder, which have high degrees of heritability. But experiences matter in myriad ways. Babies living with depressed mothers, for example, have poorer exploratory skills and flatter affects than other kids signs of depression taking hold in the babies themselves. When those kids are given electroencephalograms, their brain tracings turn out to be flatter too. When a depressed mother is treated, her baby's emotional state may improve as well.
Chronic stress can have a similar impact on the brain. In a 2010 study, psychologist Nim Tottenham of Weill Cornell Medical College in New York City conducted magnetic-resonance-imaging scans of the brains of 78 children (9 years old on average; babies would never hold still long enough), about half of whom had spent part of their early lives in orphanages. She also conducted behavioral tests on the kids' emotional-regulation skills. In general, she found that the later the children had been adopted and thus the longer they'd been institutionalized the larger their amygdalae were. (The amygdala governs emotions such as fear and alarm.) Those kids also performed worse on the emotional test. Another 2010 study of abused children yielded similar findings.
Even the subtler pressures of the home combative parents, economic hardship, parental substance abuse can do long-term damage. "Babyhood has its stresses," says Dr. Jack Shonkoff, professor of child health and development at the Harvard School of Public Health. "But the system is designed to get back to baseline. If it doesn't, it can damage brain connections and destroy circuits." It's that damage that helps a genetic predisposition become a full-blown disorder.
Once a problem takes hold, it is hard to calculate the odds of recovery; the field of infant mental health is so new that most studies have tracked kids only into their later school years. But the numbers are not promising. In one study Egger conducted, 41% of preschoolers with an anxiety condition were still impaired by it four years later. Children with preschool depression were six times likelier than other kids to have the condition later in childhood. "The nature of psychiatric conditions is that they're chronic," Egger says.
But the very malleability of a baby's brain means that the earlier a problem is caught, the likelier it can be fixed. When a child seems troubled, parents should not hesitate to seek professional advice, and parents themselves should address their own problems, including depression and substance abuse. "There's a phenomenon we call attunement," says psychologist Edward Zigler of the Yale University School of Medicine. "It's that dance of the swans between parent and baby." Moms and dads should practice that well, because before they know it, their children dance away from them completely.