Respiratory Sinus Arrhythmia (RSA), a pivotal metric of cardiac vagal tone, eloquently encapsulates the rhythmic interplay between respiration and heart rate variability, serving as an insightful proxy for the parasympathetic nervous system's regulatory prowess over the organism's comportment. Notably, RSA is heralded as a biomarker of an individual's proficiency in emotion regulation, with a higher baseline vagal tone being synonymous with enhanced regulatory capabilities and a more harmonious social engagement (Porges, 2003). The polyvagal theory concept of the "vagal brake," which delineates the variability in vagal tone in response to environmental stressors, further illuminates the system's resilience and its ability to marshal resources to navigate the vicissitudes of the environment. Intriguingly, the neonatal period's baseline vagal tone is a harbinger of maternal and paternal affectionate interactions, such as touch and affect synchrony at 3 months, underscoring the infant's innate disposition towards social engagement and emotion modulation as catalysts for parental tactile behaviors (Feldman & Eidelman, 2007). This biological predilection for social connectivity is also mirrored in the developmental trajectory of vagal tone in preterm infants, which bears a significant correlation with the quality of mother-infant synchrony at the 3-month milestone (Feldman, 2006). 

The nuanced study on simulated maternal deprivation, employing the still-face paradigm with and without the intervention of touch, sheds light on the modulatory effect of maternal touch on infantile vagal tone during phases of baseline, reactivity, and recovery. Analogous to cortisol dynamics, the introduction of maternal touch during still-face episodes markedly attenuates the fluctuations in vagal tone, thereby hastening the autonomic system's return to baseline equilibrium. 

Results

This evidence underscores the profound utility of touch as a medium for fostering adaptability and resilience stimulating also the vagal tone, further entrenching its role as a cornerstone in the edifice of emotional and physiological regulation ("The Handbook of Touch: Neuroscience, Behavioral, and Health Perspectives," Springer Publishing Company).

Through this lens, the tapestry of human touch emerges not merely as a conduit for emotional exchange but as a vital instrument in the orchestration of adaptive responses, highlighting its indispensable value in the human experience.