Maternal care during early development is necessary for the acquisition of a calming response to back stroking

In many mammals, early postnatal interactions between caregivers and offspring involve rich physical contact, including stroking, holding, and grooming. Offspring typically remain calm and close to the caregiver during such stimulation. Although these behaviors are widely believed to support emotional regulation and bonding during infancy, the underlying biological mechanisms and the role of prior experience in eliciting the calming response remain poorly understood. Here, we demonstrate that back stroking induces a conserved calming response in both human infants and mouse pups, characterized by reductions in spontaneous movement and heart rate. In mouse pups, stroking further facilitated sleep onset, increased EEG delta power, and attenuated stress-induced corticosterone elevations. These sleep-promoting and stress-buffering effects were absent in artificially reared pups deprived of postnatal maternal contact, underscoring the importance of early tactile experience. Transcriptomic analysis revealed downregulation of the voltage-gated calcium channel subunit gene Cacna1b in the hypothalamus of artificially reared pups. Moreover, targeted knockdown of hypothalamic Cacna1b in maternally reared pups abolished stroking-induced reductions in movement and heart rate, as well as the increase in delta power. This study identifies a conserved, experience-dependent calming response to affiliative tactile input, biologically embedded through plasticity, that supports physiological regulation and stress resilience during early development. While the developmental plasticity of discriminative tactile sensation has long been recognized, our results highlight that affiliative tactile sensation similarly depends on early experience to organize neural mechanisms regulating internal states.