For too many new mothers, what should be a time of joy is instead one of darkness visible: between 5 and 25 percent experience depression, and the rate may exceed 40 percent among low-income and teenage moms. A depressed mother tends to withdraw from her children, becoming disengaged and nonresponsive—a less extreme version of the emotional and social deprivation that young children suffered in the notorious Romanian orphanages.
In those orphans, twin brain structures called the amygdala tended to be larger than in children reared by engaged, loving parents. Now a new study finds that the brains of children who grow up with a mother who suffers from depression show the same change. Their amygdalas, whose job it is to scan the environment for threats and learn what to be afraid of, as well as to assign emotional significance to experiences and information, are also “significantly larger” than those of children whose mothers do not suffer from depression.
The study, published this week in Proceedings of the National Academy of Sciences and led by Sonia Lupien of the Université de Montréal, was small: it examined 17 children whose mothers had been depressed since their birth (all in 1996) and 21 whose mothers had not been depressed. On average, the children of depressed mothers had amygdalas measuring 1085 cubic centimeters, while those belonging to children of healthy mothers measured 879 cubic centimeters, a difference of 19 percent. The findings are in line with those from the orphans studies as well as from lab animal studies. The latter find that poor caregiving and being separated from one’s mother lead to accelerated growth of the amygdala.
Poor maternal care due to depression seems to trigger the same brain change as when the mother is entirely absent, as is the case with orphans raised in an institution. That suggests that “the amygdala is quite sensitive to the quality of maternal care,” says Lupien.
Until now, most research on the brain changes caused by stress has focused on the hippocampus, which processes memories. (The focus was so blinkered that these scientists are known as “the hippocampus mafia.”) In depressed people, for instance, the hippocampus tends to be smaller than in healthy people.
That the amygdala should be larger in children whose mothers have suffered depression for all 10 years of the kids’ lives makes sense, however. “If you grow up in an environment in which you don’t have all the support you would need, especially to help you evaluate the environment, maybe you become a super-detector of threats,” suggests Lupien. “We think it might lead to resilience.” That is, the brain of a child raised by a mother who is withdrawn and emotionally neglectful adapts by enlarging the amygdala, becoming better attuned to the threats in the environment that Mom might not be around to protect him from.
One way that might happen is by flooding the brain with stress hormones called glucocorticoids, whose production the amygdala triggers. Levels of these hormones in the children of depressed mothers soared when they were put in an unfamiliar situation, showing that their stress-response system goes into overdrive at the slightest provocation. Since it’s the amygdala that processes the feeling of threat, a larger amygdala might be the equivalent of having not one fire alarm but many go off at the slightest whiff of smoke.
Other studies have found that an enlarged amygdala may be related to autism. In this case, the thinking is that being ultra-sensitive to the presence of threats—something an enlarged amygdala might cause—brings about the social withdrawal and self-soothing behavior typical of children with autism. If the children in the Montreal study were at risk of autism, however, it would have shown up by age 10. More likely, the enlarged amygdalas produced subtler effects, making them warier and more alert to threats.
The Montreal scientists don’t know whether the amygdalas in the children of depressed mothers will remain forever enlarged, let alone what the consequences of that might be. But the revolution in neuroplasticity that has swept neurobiology in the last decade, showing that the brain can change in both structure and function in response to experiences, suggests that what can be enlarged by one environment can be returned to normal by another. “If the brain responds so fast to the environment [of having a mother suffering from depression for 10 years], it implies that an intervention could also change its developmental trajectory,” says Lupien. Home visits by nurses, enriched day care, relatives, and others pitching in to help a depressed mother raise her kids—any and all of these, she says, “could mitigate the effects of parental care on the developing brain.”