New UI study shows diminished brain response to natural “reward” in drug abusing mothers.

While most mothers experience a “natural high” when they see their baby smile, a new study shows that the brain’s reward center appears to be turned off in mothers with drug addiction problems.

In the second of a multi–phase study looking at how addicted mothers process their babies’ facial expressions, University of Iowa researchers believe they may have also found a biological link between drug abuse in mothers and caregiving problems.

This could play into why addicted mothers sometimes abuse, neglect, or lose their children to foster care, says senior author Lane Strathearn, MD, PhD, professor, developmental and behavioral pediatrics in the UI Stead Family Department of Pediatrics and University of Iowa Stead Family Children’s Hospital.

“We wanted to understand what’s actually happening in a mother’s brain when she engages with her baby, when there are complicating drug addiction problems,” Strathearn says.

The study was recently published online in the journal Human Brain Mapping. Strathearn collaborated with Sohye Kim, PhD, assistant professor in the Department of Obstetrics and Gynecology at Baylor College of Medicine.

The five–year study, funded by the National Institute of Drug Abuse, used functional magnetic resonance imaging (fMRI) to examine brain activity in 36 mothers who used addictive substances during pregnancy. The brain scan allowed researchers to observe how the mother’s brain reward mechanisms responded when she looked at her baby’s face, compared to when she looked at the face of an unknown baby.

When addicted mothers saw their babies’ smiling faces, the reward regions in the brain were not activated. In fact, these mothers had a stronger reward response with the unknown baby than with their own babies.

Researchers compared this information to previous studies done on non–addicted mothers, which showed a powerful reward response to their smiling baby, which is thought to reinforce caregiving behavior.

“This is what you’d expect from a new mother interacting with her baby – you want her to be motivated to continue caring for her baby, despite feeling exhausted when her baby is crying. You want a brain response that’s going to help her to continue to provide the care that her baby needs,” Strathearn says.

However, addicted mothers don’t appear to be receiving this reinforcement. It is as if their reward system is turned off while looking at their own babies, Strathearn says.

“I think in one way it helps us to be empathetic toward women who struggle with addiction, to understand why they may have difficulties connecting with their own baby,” Strathearn says. “Also, I think it helps us to know where we need to focus our attention to help these mothers. Treatment should focus on the mother–infant relationship, not just the drug use.”

The research team is currently exploring how a mother’s own early life trauma may influence reward processing in the brain, and possibly predispose to drug addiction. An upcoming study, also funded by the National Institute of Drug Abuse, will administer the bonding hormone oxytocin to mothers to find whether this can enhance the brain’s reward response in addicted mothers.

“We want to try to better understand what’s behind this diminished reward response in these mothers. Is it the addictive drug that is physically changing the brain? Or could it be that their own history of trauma has affected how these reward systems have developed in their brain?” Strathearn says. “That’s where we’re heading next.”