New research has shown that babies of mothers experiencing postnatal anxiety have more difficulty processing both happy faces and fearful faces, highlighting the importance of mother-infant interactions in the development of emotional processing.

The first year of life is a critical period for development of the neural circuitry that enables us to process other people's emotional expressions, which is why the researchers focused on infants 5, 7 and 12 months old, said Lindsay C. Bowman, an assistant professor of psychology at the University of California, Davis, and the lead author of the study published May 16 in The Journal of Child Psychology and Psychiatry. 

"We wanted to look at this early window in the first year of life to see if these effects of maternal anxiety are present in the infant's developing brain," she told The Academic Times. "If they are, that has potentially big consequences for how we think about educating new parents and what information we could give them when they're leaving the hospital."

Researchers have previously estimated that between 15% and 40% of new mothers experience postnatal maternal anxiety. The phenomenon has been linked with emotional problems for children, though the strength of the relationship remains unclear. 

"This is incredibly relevant because it's such a common thing, especially for new moms," Bowman said. "These aren't obscure things we're measuring that are rare but interesting; this is a pretty pervasive phenomenon. We're finding that something as common as maternal anxiety has these real impacts on the patterns of neural responses to emotional faces." 

Studies have also shown that mothers with postnatal anxiety are less emotionally responsive to their babies and talk to them in muted tones. 

"In order for us to think there may be some effect on the infants' developing brain, we would need to first know that there's something different about moms with anxiety," Bowman explained. "They have a reduced emotional tone and have a flatter affect — so, generally, reduced intensity and variability of emotions — and also respond differently to their babies. When babies are doing these little bids for attention, cooing at things, moms who are highly anxious tend not to respond in contingent ways."

Bowman and her colleagues recruited 142 pairs of mothers and infants to participate in their experiment. The infants sat on their mothers' laps and viewed a mix of emotionally expressive faces — specifically, women showing their versions of angry, happy and fearful expressions — while the researchers measured the infants' neural responses with an electroencephalogram, which detects electrical activity in the brain through electrodes placed on the scalp. The mothers were blindfolded during the experiment so that their responses to the images did not influence their baby's responses. 

"Of course, every baby had a slightly different brain response," Bowman said. "What we wanted to know is if the differences in the ways those babies' brains responded could be explained by the differences we can detect in the moms' report of their anxiety." 

The researchers found that the babies of mothers who reported higher levels of anxiety showed different neural responses to fearful and happy faces — but not to angry faces, which "may be salient to infants regardless of maternal anxiety status," the authors noted. Most critically, one pattern of brain activity known as the negative central component, which occurs after viewing an event of interest, was amplified in the babies of anxious mothers when viewing fearful and happy faces, suggesting they were struggling to process those expressions. 

"Moms who are anxious are probably not showing various expressions as intensely as other moms — there's that reduced emotional tone, that flat affect, that lack of contingent response to the baby's own expressions," Bowman said. "That means that when you show a baby these really big expressions — here's what a big, fearful face looks like — the baby's brain is like, 'Hey, what? I don't normally see that, so I have to devote additional neural resources to process this face that, in my world, is unfamiliar.'"

The findings are limited, in that the anxiety levels of the mothers who participated in the study were self-reported and not directly observed. The next step of Bowman's research will seek to confirm that the differences in babies' neural responses to emotional faces are related to less emotional expression from their mothers through the direct observation of infant-mother interactions, she said. The ongoing project will also explore whether these brain responses are observable after the first year of life by testing toddlers. 

Although longitudinal research would be required to establish whether these early neural responses to maternal anxiety could influence the child's behaviors in adolescence and adulthood, Bowman suspects that early experiences with emotional processing reverberate for a lifetime. 

"What happens early in life sets the stage for what happens later in adulthood," she said. "If we want to understand the downstream consequences for children who later develop anxiety or have aberrations of attention to emotional stimuli in their world, it's useful to look back at the first year of life, as the infant is learning about their world." 

The study, "Infants' neural responses to emotional faces are related to maternal anxiety," published May 16 in The Journal of Child Psychology and Psychiatry, was authored by Lindsay C. Bowman, University of California, Davis; Sarah A. McCormick, University of Massachusetts; Finola Kane-Grade, Boston Children's Hospital; Wanze Xie and Michelle Bosquet Enlow, Boston Children's Hospital and Harvard Medical School; and Charles A. Nelson, Boston Children's Hospital, Harvard Medical School and Harvard Graduate School of Education.