Post-natal depression? Don't blame raging hormones: the brains of women with post-natal depression process negative emotions differently to new mothers without the condition.
Mary Phillips at the University of Pittsburgh, Pennsylvania, and colleagues, used functional MRI scans to compare the brains of 14 women with post-natal depression and 16 new mothers without while they looked at pictures of angry and sad faces.
They found that the depressed women had less activity in the dorsomedial prefrontal cortex - an area of the brain thought to pick up on emotional cues and mediate emotional responses - than the non-depressed women (The American Journal of Psychiatry, DOI: 10.1176/appi.ajp.2010.09081235).
Women with post-natal depression tend to find it hard to bond with their babies. Phillips suggests that this might be linked to a more general loss of interest in social interactions.
The team had previously found that people with depression tend to be more sensitive to negative images than people free of it. This study shows that new mothers with post-natal depression seem to buck this trend - shutting out negativity and not reacting to it.
The apparent deficit in brain activity was not seen in the healthy new mothers, she says, so it is unlikely that pregnancy alone causes the effect. But more research is needed to find out whether the deficit is caused by depression or if women with less activity are predisposed to post-natal depression.
"Ten to 17 percent of women have postpartum depression," said Dr. Diana Dell, an assistant professor of obstetrics and gynecology and psychiatry at Duke University Medical Center. But the problem is often overlooked, even by physicians, she said.
Dell partly faults society for not giving new mothers enough support. "We think you are supposed to birth your baby, pick up your grain sack and go on," she said.
But postpartum depression "is the most underdiagnosed obstetrical complication in America," added Dell, who is an obstetrician as well as a psychiatrist.
And that's troubling, she said, because talk therapy and medication can help treat the condition and get women back on track, making them healthier people and happier parents.
Another expert says adding complementary therapies to the mix, such as massage therapy, can also pay big dividends.