What happens in the brains of mothers and children when they are solving a puzzle together – do their brain waves become synchronized to one another? And how is such neural synchrony influenced by mother-child behavior and thus relationship quality? We set out to study these questions in a collaborative effort between the University of Vienna (Austria) and the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig (Germany).
When we interact with others, we naturally get ‘in sync’ with our interaction partners. This phenomenon is known as bio-behavioral synchrony. Defined as time-locked processes of biology and behavior, bio-behavioral synchrony is nowadays understood to most prominently occur at four levels: (i) behavior – e.g. eye gaze, touch, verbalizations; (ii) physiology – e.g. heart rate, breathing frequency; (iii) endocrinology – e.g. secretion of cortisol or oxytocin; and (iv) neural activation – e.g. simultaneous de- and increases of brain activity. Through research pioneered by Ruth Feldman (Interdisciplinary Center (IDC) Herzlia), bio-behavioral synchrony was furthermore shown to be stronger within most intimate and close relationships – e.g. parent-child pairs & romantic partners – as compared to interactions with friends, acquaintances or strangers.
Although it has recently been shown in several studies using either electroencephalography (EEG) or functional near-infrared spectroscopy (fNIRS) that mother and child brain activity becomes synchronized during natural play, it remains largely unknown how neural synchrony relates to mother-child behavior and thus relationship quality. In other words, does the degree of bio-behavioral synchrony during social interaction not only differ as a function of relationship intimacy and closeness – and thus between different relationship categories -, but maybe even within categories as a function of inter-individual differences in relationship quality? And if so, could bio-behavioral synchrony more generally, and brain-to-brain synchrony more specifically, serve as a new measure for relationship quality? Preliminary data from a previous study we conducted in mother-child pairs at Stanford University by associating brain-to-brain synchrony during a computerized reaction time task with child attachment to the mother suggests it may.
In the present investigation, 42 dyads of mothers with their pre-school children (age 5-6 years) were assessed with fNIRS while they played a puzzle-solving task (tangram). They either got one set of puzzle blocks for both of them and had to re-create templates by cooperating with each other, or got one set of puzzle blocks each and had to solve the task independently of each other (while being separated by an opaque screen). There was an additional resting phase condition where both mother and child relaxed with their eyes closed. We measured brain activity at two sites over the dorsolateral prefrontal and temporal lateral cortex. These regions are known to be involved in executive functioning & complex decision making and the sharing of psychological states.
Our results revealed increased brain-to-brain synchrony during cooperative as compared to individual puzzle-solving (and rest) across both assessed brain areas, which accords with previous findings from our own and other groups.
Furthermore, we found that the degree of brain-to-brain synchrony during cooperation was higher the more puzzle templates the mother-child pairs were able to re-create. This shows that neural coupling is essential to social information exchange and underlines the role of neural synchronization for cooperative task performance.
Most importantly, however, we observed that the degree of brain-to-brain synchrony during cooperation varied as a function of mother-child behavior. The more reciprocal the mother-child interaction was during cooperation (i.e. the more responsive and contingent turntaking behavior was), the higher was the brain-to-brain synchrony. Similarly, the more autonomous the child was allowed to behave (i.e. the more the child was able to engage in the task instead of being led by the mother = high child agency), the higher was the brain-to-brain synchrony. Both above findings suggest that higher mother-child interaction quality associates with increased brain-to-brain synchrony particularly during cooperation.
Overall, our results shed light on cooperation as a function of brain-to-brain synchrony during mother-child interaction and point towards brain-to-brain synchrony being a neurobiological marker of mutual engagement and successful coordination in social interactions. We are continuing to investigate bio-behavioral synchrony and its association with relationship quality in parent-child dyads by also including father-child pairs and more specifically testing for inter-individual differences in attachment as part of our interdisciplinary and collaborative CARE Studies.
Nguyen, T., Kayhan, E., Schleihauf, H., Matthes, D., Vrtička, P., Hoehl, S. (2020; available online December 20th 2019). The effects of interaction quality on neural synchrony during mother-child problem solving. Cortex, Volume 124, Pages 235-249, OPEN ACCESS.
https://doi.org/10.1016/j.cortex.2019.11.020.
Dr Pascal Vrticka (PhD, FHEA) 
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