A new study links a stress hormone in pregnant mothers to larger amygdalas in children, meaning potential headaches when it comes to emotional development.
In previous research, we've learned that the size of the amygdala -- the part of the brain responsible for handling emotional response and threat perception -- can have an impact on our political outlook and the number of friends in our social networks. Now, a new study finds that maternal stress may be linked to amygdala volume in children, opening up new questions about how many of our social skills are shaped before we're even born.
In a paper published in the Proceedings of the National Academy of Sciences last month, researchers reported that mothers who experienced greater levels of stress during pregnancy tended to produce girls with larger amygdalas. After seven years, these offspring displayed more symptoms of affective disorders.
The scientists had mothers in the study undergo a saliva swab at 15 weeks of gestation to measure for stress hormones. Mothers who had more cortisol in their blood gave birth to girls whose right amygdalas were slightly larger, though the pattern didn't hold for boys. A one-standard deviation increase in maternal cortisol meant, on average, a 6.4 percent increase in amygdala size.
What's more, the girls who had larger amygdalas scored worse on the Child Behavior Checklist, a standard questionnaire designed to suss out behavioral problems in young people. "Susceptibility for affective disorders may, in part, be programmed in utero," the researchers concluded. "This effect may be mediated through changes in anatomy of the amygdala."
If the science is true, it offers another possible explanation for variations in brain physiology from person to person -- as well as why some people are more comfortable with uncertainty than others. It could also help explain why girls tend to experience mood disorders at greater rates than boys, a situation that until now was thought to be due to hormonal developments after birth or linked somehow to social expectations, said Victor Carrion, a Stanford professor in pediatric psychiatry.
"Even before you hit puberty, there may be things going on in the in-utero environment of girls that may render some girls more vulnerable to these affective symptoms," said Carrion in a phone interview. "So one possibility is that girls develop earlier -- as we know they do -- but that this translates very early in utero."
Update: Heidi Feldman, a Stanford professor of pediatrics in neonatal and developmental medicine, threw some cold water on the paper in a phone interview late Tuesday, saying the children at age 7 who'd been born to higher-stress mothers didn't appear to be much more emotionally challenged compared to those born to mothers under normal amounts of stress. Citing the study's own figures, Feldman pointed out that the difference between the two groups on a scale of affective symptoms was only a matter of two or three points.
"These girls are scoring very, very close to the the normal level," she said. "The mean for the girls is about 52 in this high cortisol group, compared to 50 for the control. None of these girls at age seven are extremely abnormal in their scores."
Feldman added that an abnormal score would be about ten points higher. While this doesn't necessarily invalidate the paper's findings, it's a good reminder that all research is a work in progress.