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 thought to support emotional regulation and bonding during infancy, the underlying mechanisms and the role of prior experience remain unclear. Here, we demonstrate that back stroking induces a conserved calming response in both human infants and mouse pups, characterized by reduced 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, knockdown of hypothalamic Cacna1b in maternally reared pups abolished stroking-induced calming and sleep-promoting effects. 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. Our results highlight that affiliative tactile sensation, like discriminative tactile sensation, depends on early experience to organize neural mechanisms regulating internal states.