Tiny shifts, major ripples: Unravelling micro-mechanisms in the building of mother-infant attachment and psychophysiological regulation.

Parental nurturing touch plays a crucial role in early infant development by activating C-Tactile afferents, which trigger neurobiological pathways essential for parent-infant bonding and the building of attachment. This process is said to regulate the infant's parasympathetic nervous system, fostering emotional and physiological connection with the caregiver. Research has consistently shown that CT-mediated touch enhances infant parasympathetic tone, yet no clear patterns of mutual co-regulation between parent and infant have been reported. Here, we replicated our previous study design to test the impact of three minutes of maternal stroking touch on mother-infant cardiorespiratory regulation, using no-touch pre- and post-stroking baselines. To control for potential confounds, we standardised the infant's holding position, used active baselines (i.e., active group) instead of resting baselines (i.e., resting group) to account for maternal metabolic activity, and compared stroking with and without massaging oil in the active group. Electrocardiogram (ECG) and respiration were measured in 30 mother-infant dyads (active group) and 24 mother-infant dyads (resting group) (infants aged 5-14 weeks) to calculate RRI-intervals (RRI), respiration frequency (fR), and Respiratory Sinus Arrhythmia (RSA). Surprisingly, no significant changes in mother and infant cardiorespiratory measures were observed in the active contrary to the resting group and the use of massaging oil had no notable impact in the active group. We suggest that these lack of changes show that subtle experimental manipulations have an influence on maternal-infant co-regulation, emphasising the importance of using research designs that respect the individualised ecological environment of parent-infant interactions and the role of micro-processes and multisensory integration in shaping regulatory attachment dynamics.