Bilingual mothers and children synchronize brain activity equally in both languages during play

When a mother plays with her young child in a language she learned as an adult rather than the one she grew up speaking, something might seem to be lost - a naturalness, a fluency, an emotional register that feels slightly off-key. Many bilingual parents report this sense of emotional distance when using their non-native language with their children. The question of whether that perceived distance corresponds to any measurable difference in the brain-to-brain connection between parent and child has now been addressed in a small but carefully designed study published in Frontiers in Cognition.

The answer, at least for the 15 mother-child pairs studied, is no.

Researchers at the University of Nottingham, led by Dr. Efstratia Papoutselou and Professor Douglas Hartley, recruited families in the UK where children between three and four years old had been raised bilingually. English was not the mothers first language, but all had achieved C1 or C2 proficiency - the highest levels defined by the Common European Framework of Reference for Languages, indicating near-native or native-equivalent command.

Measuring brain synchrony with fNIRS

Each mother-child pair visited the research clinic and sat at a table with toys. Both wore a cap fitted with fNIRS (functional near-infrared spectroscopy) sensors - a non-invasive imaging technology that measures changes in blood oxygenation across the brain surface as a proxy for neural activity. Both participants were measured simultaneously, allowing the researchers to track the degree to which the neural activity of mother and child fluctuated in tandem - a measure known as interbrain synchrony.

The pairs were assigned to three conditions in randomized order: playing together freely in the mother native language, playing together exclusively in English, and playing silently and independently with a screen separating them. The silent, independent play condition served as a baseline for comparison.

Synchrony was strongest in the prefrontal cortex - a brain region involved in decision-making, planning, reasoning, and emotional regulation. It was weaker in the temporo-parietal junction regions, which regulate social cognition and attention. Synchrony was significantly stronger during interactive play than during silent, independent play across both language conditions, confirming that the social interaction itself drives the neural alignment.

No difference between languages

The critical comparison - native language play versus English play - showed no statistically significant difference in interbrain synchrony. Mothers and children synchronized their neural activity just as effectively when communicating in English as when using the language the mothers had grown up speaking.

"Here we show that the brains of bilingual moms and their kids stay just as in sync through neural synchrony irrespective of whether they play in the mom native language or in an acquired second language," said Dr. Papoutselou. "This is an important finding because it suggests that using a second language does not disrupt the brain-to-brain connection that supports bonding and communication."

The finding is perhaps unexpected given that even highly proficient second-language speakers tend to speak their acquired language more slowly, with more pauses and self-corrections, particularly in emotionally charged contexts. Previous research has found that bilingual speakers often report a sense of emotional distancing when using their non-native language. The neural synchrony data suggests this subjective experience does not translate into a measurable impairment of parent-child brain coordination during interactive play.

Limitations of a small pilot study

The most significant limitation of this research is its sample size. Fifteen mother-child pairs is a small number for drawing broad conclusions, and the study focused specifically on a narrow demographic: bilingual families in the UK where English was the acquired second language, with children in a specific developmental window of three to four years. The mothers were all highly proficient English speakers (C1 or C2), meaning the findings may not extend to parents with lower proficiency whose second-language fluency is more impaired and whose speech patterns in that language might be more disrupted.

The fNIRS method measures blood oxygenation changes at the brain surface and cannot reliably capture activity in deeper brain structures. It is also sensitive to head movement - a particular challenge in studies with young children. The naturalistic play paradigm was designed to minimize artificiality, but lab settings inevitably differ from home environments where language use patterns develop organically.

Despite these constraints, the study contributes a novel data point to the neuroscience of bilingualism and parent-child interaction. "Bilingualism is sometimes seen as a challenge but can give real advantages in life," said Professor Hartley. "Our research shows that growing up with more than one language can also support healthy communication and learning."