Pandemic-era children show altered brain responses to facial expressions, new study finds

A large study published in Developmental Cognitive Neuroscience has found that children who were tested during the COVID-19 pandemic showed measurable differences in how their brains processed faces, especially emotional expressions. While some aspects of face perception remained stable, the research found that three-year-olds processed faces faster and, across all age groups, children had reduced neural responses to happy faces, suggesting changes in how familiar or attention-grabbing these expressions were.

The researchers were interested in whether the social restrictions introduced during the pandemic, such as reduced in-person interactions and widespread mask-wearing, may have shaped early brain development. Infants and toddlers learn a lot from observing faces, including how to recognize people and interpret their emotions. The team wanted to know whether a reduced variety of facial exposure might influence how children process faces, how quickly they do so, and whether they can distinguish between different emotional expressions.

“There have been several studies suggesting that input is crucial for the early development of processing emotional faces. This, however, has mainly been studied in extreme cases such as neglect, or in more indirect ways such a relating parental traits to children’s face processing,” explained study author Carlijn van den Boomen, an assistant professor at Helmholtz Institute Utrecht University.

“The policies taken to mitigate the effects of the COVID-19 pandemic included several things that affected the social interaction, and thus the input that children received. This was happening on a very large scale, as it likely affected almost all children in (Western) countries.”

“I was curious from a theoretical perspective, as never before could we study the effects of reduced variety of social input on such a large scale. Moreover, I found it important that this would be investigated, given that it affected so many children: policy makers and parents should know about the effects the policies had on children.”

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To investigate, the researchers used electroencephalography (EEG) to measure brain activity in over 900 children aged 5 months, 10 months, or 3 years. Some children were tested before the onset of the pandemic, while others were tested during the period when COVID-19-related government policies were in place, between March 2020 and April 2022. This allowed the researchers to compare brain responses in children who had typical social exposure to those whose early years were shaped by limited interactions and more frequent mask use in adults.

Children in the study passively viewed a series of images that included neutral faces, happy faces, fearful faces, and houses. EEG recordings focused on event-related potentials (ERPs), patterns of electrical activity that occur in response to specific stimuli. The researchers analyzed three well-known ERP components linked to face processing: the N290, P400, and Nc. These components reflect different aspects of visual and emotional processing, including how fast faces are recognized and how emotionally meaningful or familiar they are perceived to be.

When it came to how quickly the brain responded to faces, the researchers found no meaningful differences in 5- or 10-month-old infants between those tested before and during the pandemic. However, in three-year-olds, there was a notable difference. Children tested during the pandemic showed earlier N290 responses to faces than their pre-pandemic counterparts, indicating faster neural processing of facial information. This was specific to faces and not observed when children looked at images of houses.

The finding of faster face processing was somewhat unexpected. In typical development, the speed at which the brain processes faces increases with age and experience. However, some previous research in adults has shown that reduced facial information — such as when faces are masked — can lead to quicker processing.

In contrast, the ability to tell the difference between faces and non-facial objects, known as face categorization, appeared unaffected by the pandemic. Across all age groups, children tested before and during the pandemic showed similar patterns of brain activity when viewing faces versus houses. This suggests that this fundamental aspect of face processing is resilient and may not depend as strongly on a wide range of facial experiences.

However, the most striking differences emerged when the researchers examined how children responded to emotional expressions. Children tested before the pandemic showed distinct patterns of brain activity when viewing happy, fearful, and neutral faces. But among those tested during the pandemic, this differentiation was reduced or absent.

In both ten-month-olds and three-year-olds, brain responses to happy and fearful faces became less distinguishable, especially in the later ERP components, the P400 and Nc, which are thought to reflect attention or familiarity.

“Even though we expected effects of the policies on emotional face processing, it was surprising to see that these were so clear, and present in all tested age-groups,” van den Boomen told PsyPost. “Particularly the 3-year-olds likely did process emotional expressions before the pandemic (as they learned this in their first year, which was pre-pandemic). It was surprising, and as a parent somewhat unsettling, to find that even these children were so severely affected.”

These differences were particularly driven by a reduced neural response to happy faces. While children in the pre-pandemic group showed stronger brain responses to happy expressions, those tested during the pandemic had weaker responses. This pattern suggests that happy faces were either less familiar or attracted less attention in the post-pandemic group.

The researchers propose several possible explanations. One is that the variety of happy expressions that children saw may have decreased during the pandemic, due to both mask-wearing and the emotional toll experienced by caregivers.

If children saw fewer smiling faces, their brains may have become less attuned to recognizing and reacting to them. The brain’s emotional face processing system is known to be shaped by experience, especially during early development. Just as infants need to see a variety of faces to build a robust mental representation of them, they may also need a range of emotional expressions to learn how to distinguish them.

“This study shows how important social experience is for shaping the social brains of children,” van den Boomen explained. “The policies taken to mitigate the effects of the COVID-19 pandemic affected the social experience of young children. Consequently, brains of children tested during the pandemic did not differentiate between facial emotional expressions, while children tested before the pandemic did. Facial expressions of emotions are important cues in social and cognitive learning.”

“As such, the limited processing of such cues can have far-reaching consequences for the further development of children. This is important to know for policy makers, and for parents of and practitioners working with children that were 0-4 years old during the pandemic. Moreover, this insight could also benefit children born in non-pandemic times children, as they benefit from a variety of social experiences as well.”

The study does come with some limitations. While the researchers inferred that children tested during the pandemic had reduced facial input, they did not measure the exact nature or frequency of children’s social interactions. It’s possible that some families maintained relatively typical social environments, while others experienced more extreme isolation.

Other factors, such as parental stress, mental health, and daycare attendance, may also have influenced the outcomes. Additionally, while brain activity patterns were measured, the study did not assess behavioral responses, such as whether children could label or respond appropriately to different facial expressions.

“We hope to test long-term effects of the policies: hopefully, the social brains of children have caught up and (re)learned to differentiate between facial expressions after the pandemic,” van den Boomen said. “Furthermore, we’d like to test whether there are inter-individual differences in how much the policies affected emotional face processing of a child.”

“Please know that I support the policies taken during the pandemic,” she added. “I’d not like to contribute to criticism on these policies, but do find it important that the effects are known and limited by further policies (e.g. support for children with social problems).”

The study, “The effects of Covid-19 related policies on neurocognitive face processing in the first four years of life,” was authored by Carlijn van den Boomen, Anna C. Praat, Caroline M.M. Junge, and Chantal Kemner.