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Biological basis of togetherness in mother-infant dyads

One of the reasons why I chose to pursue my research career into the field of developmental psychobiology was the same question that Louis Sander beautifully reported to be his major drive and curiosity on human nature: How are we supposed to be able to be separated (individuals) and - at the very same time - connected to each other (dyadic systems)? Most certainly, this is also one of the native questions at the dawn of infant research in the early '70s of the 21st century. As many researchers began to be fascinated and seduced by Louis Sander call to curiosity in this field, the notion that our biology - in some secret way - predisposes us to be together-with and still separated-from each other gradually gained its credibility on the scene of developmental science. Some years after introducing myself to this field of scientific investigations, I finally managed to study this topic from a specific perspective.

In a brand new paper published on Psychoneuroendocrinology, we have documented how 3-month-old preterm and full-term infant dyadically regulate together with their mothers their reciprocal neuroendocrine systems (i.e., hypothalamic-pituitary-adrenal, HPA axis) during stressful conditions. Partly due to the early experience of reiterated pain-related stress during the hospitalization in the Neonatal Intensive Care Unit (NICU), preterm infants are at risk of developing a down-regulated HPA axis (i.e., dampened salivary cortisol reactivity to stressful conditions), a pattern of neuroendocrine functioning which is common in organisms exposed to chronic stress exposures. Nonetheless, we know little about the co-regulation of the HPA axis in mother-infant dyads after preterm birth.

So, the question is: are preterm infants and their mothers less, more or equally able of dyads of full-term infants in regulating their HPA axis in a coordinated and attuned way? And - most importantly - is there a unique way to co-regulate neuroendocrine stress systems in a mother-infant dyad (Bernard et al., 2017)? In this study, dyads of preterm and full-term infants and their mothers took part in a well-established procedure for stress regulation assessment in infants, i.e., the Still-Face procedure. During this paradigm, the mothers are instructued to show a still face to their infant for a very brief period, thus resulting in an age-appropriate state of stress that allows to assess both biological and neuroendocrine stress reactivity in infants (Provenzi et al., 2016). Furthermore, we employed two different metrics of HPA axis co-regulation: one that is meant to depict the ongoing regulation across multiple time-points (i.e., in-time synchrony) and one that capture the within-dyad correlation of salivary cortisol concentration in each specific time-point (i.e., in-moment coupling).

Findings revealed that both dyads of preterm and full-term infants and their mothers showed evidence of some kind of co-regulation of their HPA axis across the Still-Face procedure. Notwithstanding, while dyads of full-term infants showed a sort of complimentary regulation of the HPA axis, with infants increases corresponding to maternal decreases and viceversa, in dyads of preterm infants a less reciprocal pattern emerged, with significant in-time synchrony, but non-significant in-moment coupling.

[...] Indeed, the in-moment coupling and the in-time synchrony measures contributed to depict a complex pattern of coordination of HPA axis activity between healthy FT infants and their mothers while facing a socio-emotional stress exposure. [...] Furthermore, the overlying and less dynamic pattern of HPA axis coordination observed in VPT infants might suggest either an adjustment to the early NICU hospitalization and/or a risk factor for further infant and child socio-emotional development later in life [...] (Provenzi et al., 2018)

So far, it is not possible to conclude on the adaptive or maladaptive value of different ways of co-regulating neuroendocrine stress response in mother-infant dyads. And probably, the questions of adaptation is not the correct one. What is certain, is that the early history of NICU hospitalization appears to be enough to modify the way through which our biology predisposed us to togetherness at the biological level. This kind of dyadically-characterized and biological-based "regulation knowledge" contributes to what can be cosidered the footprint of our past experiences on our future developmental trajectories. These findings indirectly highlight the relevance of investing in early intervention and family-centered protective care in the NICU. Taking care of preterm infants and their mothers - and let them be together since the very beginning of infant's post-natal life - should be considered a key goal of NICU care.


More details on this study can be found in the original paper:

Provenzi L, Giusti L, Fumagalli M, Frigerio S, Morandi F, Borgatti R, Mosca F, Montirosso R (2018) The dual nature of hypothalamic-pituitary-adrenal axis regulation in dyads of very preterm infants and their mothers. Psychoneuroendocrinology, in press.

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