Babies get the limelight, but what happens to mothers’ brains after birth?


“Most people have at least one or two stressors in their lives. But when mothers are experiencing multiple major stressors at the same time, it can be really overwhelming. It puts them at greater risk for postpartum depression and negative mother-infant relationships.” — Pilyoung Kim, University of Denver

We’ve learned a great deal in recent years about the dramatic changes children’s brains undergo in the first years of life. But what about their parents’ brains — do they undergo big changes, too?

Pilyoung Kim, a research professor at the University of Denver, specializes in studying mothers’ brains. Her research started with a question she had formulated after having her own children and realizing how difficult parenting was: Given the incredibly high demands of parenting, why are parents willing to spend so much time and energy on their infants?

Previous research had established that pregnant women’s brains undergo synaptic pruning, resulting in significant reductions in the brain’s gray matter. Researchers believe this pruning helps prepare the brain for motherhood.

But Kim wanted to know more about what happens to mothers after they give birth. So she organized a longitudinal study, using MRI scans to track the changes in the brains of 19 first-time mothers. Her team found that in the first few months after having a baby — known as the postpartum phase — the new mothers’ brains substantially increased in gray matter, particularly in the regions associated with sensory, motor, cognitive and emotional processing.

“The brain has a number of connections that we call the reward circuitry,” Kim explained. “It responds to anything that makes us feel very good. What we discovered was that after we give birth, this brain area is particularly sensitive to infants and infant cues, especially those of our own.” The study found that a mother’s positive thoughts about her baby significantly predicted gray matter volume increase in brain regions associated most closely with the reward circuitry.

A caregiver’s ability to pick up on and respond to cues from a baby — a dynamic often known in child development circles as “serve and return” — is a fundamental building block for child brain development. When an infant babbles, cries, or gestures, and the caregivers respond consistently and appropriately, it creates and strengthens neural connections in the baby’s developing brain, bolstering communication and social skills. The baby makes sucking noises, the parent reaches to prepare a bottle. The baby starts fussing, the parent starts rocking and singing a lullaby to the baby. These interactions take all sorts of shapes, but recent research suggests it’s the quality, not the quantity of interactions that’s important for development.

But what happens if the baby serves up cues and they go unnoticed, or the parent is unable to respond? Previous research has looked at the neurological impact of stress in rat mothers. Researchers stressed the rats by creating crowded living environments, or depriving mothers of nesting materials. MRIs showed diminished brain structures and less activation in the reward and prefrontal cortex areas of the rats’ brains. The rat mothers with such high levels of stress were shown to have more anxiety and displayed less motivation to take care of their offspring.

Similar patterns can be seen in humans. After accounting for poverty and its associated stressors, Kim looked at first-time mothers’ brains through an MRI machine as they listened to recordings of their infants crying. Common sources of stress included lack of money and food insecurity, crowded and substandard housing, violence in the community, and marital problems. Mothers of color, particularly Black mothers, disproportionately face high levels stress. Research has found that the stress of being a Black woman in American society causes accelerated biological aging, with Black women on average 7.5 years biologically “older” than white women in their 40s and 50s. Such findings have serious implications for pregnancy and childbirth.

In Kim’s research, mothers with more stressors exhibited dampened neural responses to infant cries in the prefrontal cortex, a region of the brain that plays a key role in evaluating emotional and social information from infant cues as well as regulating their own emotions. Another study demonstrated that mothers with more stress had weaker responses in the amygdala — the brain’s emotion center — while looking at photos of infant faces with positive expressions, and heightened activation for negative expressions.

“Most people have at least one or two stressors in their lives,” said Kim. “But when mothers are experiencing multiple major stressors at the same time, it can be really overwhelming. It puts them at greater risk for postpartum depression and negative mother-infant relationships.”

The stress also makes moms less likely to interact with their babies in ways that are crucial for building young brains. Not only are babies unable to learn the skills they need for healthy brain development, the lack of interaction can trigger a stress response in babies that floods their brains with potentially harmful stress hormones. Over time, such “toxic stress” can have lasting repercussions on a child’s health and development.

Clinicians and researchers are looking for ways to capitalize on this critical period of brain development, for both the mother and the child. Dr. Elissa Epel, a researcher at UCSF, designed an eight-week program at the University of San Francisco’s Center for Health and Community to help low-income, pregnant, and overweight women to reduce stress and stress eating in their lives. The program, MAMAS (Maternal Adiposity, Metabolism, and Stress) Mindful Training, showed significant reductions in perceived stress and depression symptoms during pregnancy. Other programs targeting the postpartum period focus on attachment and the mother-infant relationship.

Minding the Baby, modeled on the well-known Nurse-Family Partnership program, for example provided home visits to high-risk families from pregnancy up to the child’s second birthday. These visits, conducted by nurse practitioners and social workers, foster parenting skills, support mom’s ability to reflect and read baby’s cues, and promote mother-infant relationships. Families enrolled in the program were more likely to be on track with immunization schedules in the baby’s first year of life, less likely to be referred to child protective services, and infants were much more likely to be securely attached with their mothers as measured by the aptly-named “strange situation procedure,” or how infants react to a series of incidents in which the infant is left with a stranger, then reunited with their caregiver.

“The perinatal period serves as a window of opportunity and vulnerability, when the mother’s brain is influenced by stress and pathology, but is also receptive to interventions and positive experiences,” Kim said. “We treat our mothers like candy wrappers, taking good care of them during pregnancy. What happens once the candy is out of the wrapper?”

Elissa Lee | Columnist

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