New research probing hidden responses in the brain may add to the understanding of women who are caught in depression after giving birth to a child, raising questions about their emotional connection to their infants.
Functional magnetic resonance imaging, or fMRI, of women with postpartum depression who were shown scared or angry faces showed less activity in and between two sections of the brain than the scans of healthy mothers, according to a recently published University of Pittsburgh study.
Previous research of postpartum depression has chiefly focused on the effect of hormones.
The findings of Eydie Moses-Kolko, assistant professor of psychiatry within Pitt's School of Medicine, and colleagues showed less activity to faces in the dorsomedial profrontal cortex in depressed mothers than in healthy mothers. That part of the brain helps control emotional responses and reactions to the emotional needs of others.
The small study, which involved 14 depressed and 16 healthy postpartum mothers, also showed no communication between the dorsomedial prefrontal cortex and the amygdala, the center of emotional conditioning, in the depressed mothers.
Furthermore, the research found that lower activity in the left amygdala was associated with greater depression in postpartum mothers and that lower activity in the right amygdala corresponded with depressed mothers feeling greater hostility toward their infants.
In addition to the functional MRI, the study used questionnaires to determine quality of attachment, hostility and pleasure in the mothers' interaction with their infants.
"What [the dorsomedial prefrontal cortex] is best known for is its role in social cognition, which is understanding and being in tune with other people's feelings, intentions and needs. Now in mothers you'd expect that region to be very active to any kind of emotional stimulus because mothers have the constant task of trying to read the needs of their infants, who can't speak and who use emotional facial expression and vocalizations to express their needs," Dr. Moses-Kolko said.
She noted, though, that the study, just published in an online advance edition of the American Journal of Psychiatry, did not specifically address the effect of that lowered brain activity on the depressed women's babies.
Instead, Dr. Moses-Kolko said, the researchers may have found "a neural mechanism that could explain what has been described in mother-infant behavioral literature.
"We're the first to use this paradigm with mothers in the [MRI] scanner and to report reduced activity and connections within and between these brain regions (the dorsomedial prefrontal cortex and amygdala) in depressed mothers," Dr. Moses-Kolko said.
Previous studies have shown that when there is a good connection between these brain regions "it signals intact emotional regulation," Dr. Moses-Kolko said. "Individuals can reduce the experience of negative emotions and increase awareness of other things at hand. ... It's an important circuit that helps people regulate their emotions."
Though the study did not address the potential effects of these brain activity patterns on infant caregiving in depressed mothers, she speculated that a mother with a "disengaged" amygdala and underactive dorsomedial prefrontal cortex to emotional faces "could lead her to being less attuned to a baby's expression and needs."
"There is this long history of behavioral research between mother and infant, and infants of depressed mothers are more likely to have trouble with self-regulation and later in childhood have increased risk for developmental delays, mood disorders, and conduct disorders," she said.
Dr. Moses-Kolko also said the study doesn't show that the field of medicine has been incorrect in blaming hormones for postpartum depression.
"Hormonal changes could still be contributory. We know that hormones of pregnancy and hormones of delivery and lactation are involved in modeling the maternal brain. Hormones could be very much involved, but we didn't study that directly," she said.
Shari I. Lusskin, director of reproductive psychiatry in the New York University School of Medicine, said, "We don't know what causes the [brain] changes that occur, but we do know the hormonal changes of pregnancy and the postpartum period have an impact on brain function. What we don't understand is what makes the system run amok."
Dr. Lusskin called the study a good first step.
"It examines the neural circuitry of emotional processing in postpartum depression in order to look for the causes and consequences of postpartum depression with an aim to improve detection and management," she said.
"I think with this type of study what we're seeing is a correlation between two findings but not necessarily causation. This study doesn't tell us what's doing what to what."
Regardless, Dr. Lusskin called the study "important because it helps get to the biology. It's a window on the biology of the disorder, but we have a lot further to go in truly understanding what causes this disorder and what the best means of treatment for an individual patient would be."
Because this study was small, Dr. Moses-Kolko said the researchers are hoping to get the money necessary for a much larger sample.
"We need to replicate this finding in a larger group," she said. The researchers, who used adult faces in this study, want to use infant stimuli -- infant faces or infants' cries -- to make the larger study more relevant.
"We also want to be able to relate the brain finding to mother-infant attachment in a lab setting. We used a questionnaire; next time we want to use a video tape [of mothers with their babies] to measure attachment."