“Animal studies have shown the role of dopamine in bonding but this was the first scientific evidence that it is involved in human bonding,” said Northeastern University Professor Lisa Feldman Barrett, corresponding author of the study.
“That suggests that other animal research in this area could be directly applied to humans as well.”
For the study, Prof. Barrett and her colleagues from the United States and Israel recruited 19 mother-infant pairs.
“The infant brain is very different from the mature adult brain — it is not fully formed,” Prof. Barrett said.
“Infants are completely dependent on their caregivers. Whether they get enough to eat, the right kind of nutrients, whether they’re kept warm or cool enough, whether they’re hugged enough and get enough social attention, all these things are important to normal brain development.”
“Our study shows clearly that a biological process in one person’s brain, the mother’s, is linked to behavior that gives the child the social input that will help wire his or her brain normally.”
“That means parents’ ability to keep their infants cared for leads to optimal brain development, which over the years results in better adult health and greater productivity.”
To conduct the study, the team used a machine capable of performing two types of brain scans simultaneously: functional magnetic resonance imaging (fMRI) and positron emission tomography (PET).
The scientists focused on dopamine, a chemical that acts in various brain systems to spark the motivation necessary to work for a reward.
They tied the mothers’ level of dopamine to her degree of synchrony with her infant as well as to the strength of the connection within a brain network called the medial amygdala network that, within the social realm, supports social affiliation.
“We found that social affiliation is a potent stimulator of dopamine. This link implies that strong social relationships have the potential to improve your outcome if you have a disease, such as depression, where dopamine is compromised,” Prof. Barrett explained.
“We already know that people deal with illness better when they have a strong social network. What our study suggests is that caring for others, not just receiving caring, may have the ability to increase your dopamine levels.”
Before performing the scans, the authors videotaped the mothers at home interacting with their babies and applied measurements to the behaviors of both to ascertain their degree of synchrony. They also videotaped the infants playing on their own.
Once in the brain scanner, each mother viewed footage of her own baby at solitary play as well as an unfamiliar baby at play while the researchers measured dopamine levels, with PET, and tracked the strength of the medial amygdala network, with fMRI.
The mothers who were more synchronous with their own infants showed both an increased dopamine response when viewing their child at play and stronger connectivity within the medial amygdala network.
“Our data indicate that dopamine is involved in human bonding,” the researchers said.
“Compared with other mammals, humans have an unusually complex social life. The complexity of human bonding cannot be fully captured in nonhuman animal models, particularly in pathological bonding, such as that in autistic spectrum disorder or postpartum depression.”
“Thus, investigations of the neurochemistry of social bonding in humans, for which this study provides initial evidence, are warranted.”