Social stress and affiliative touch: A tale of two affective states.

Social interactions are an integral part in the life of social species. Humans and other species, such as rats and mice, thrive on positive social interactions, whereas stressful social encounters can be among the most negative and traumatizing experiences. These traumatic experiences have often been linked to psychopathology, with some individuals being more vulnerable than others in developing maladaptations. Here, we review literature regarding both positive and negative affective states linked with prosocial/affiliative and stressful social experiences, respectively. Of all positive social interactions, social touch is a particularly potent and evolutionarily conserved behavior associated with social buffering. We examine these topics from the standpoint of both human studies and fundamental research involving rodents, as rodents are among the most commonly used model organisms. As we explore the physiological mechanisms underlying social stress and affiliative touch, our review highlights that many common brain regions are engaged in both species examined. Moreover, a substantial overlap exists in the neural substrates involved during both positive and negative social interactions. This evidence denotes the need to refine our experimental approaches to further delineate the involvement of these areas in a cell- and projection-specific manner for positive and negative social interactions. We conclude that despite the well-known buffering effects of social touch for stress and anxiety, more interdisciplinary research is needed to establish somatosensorial approaches, such as touch-based interventions, as a standard avenue in the treatment of stress-related symptomatology. We argue that social/affiliative touch could, in fact, be one of the most effective "antidotes" in the aftermath of social stress.