Touching the social robot PARO reduces pain perception and salivary oxytocin levels

Scientific Reports volume  10, Article number: 9814 (2020 ) Cite this article

Human-human social touch improves mood and alleviates pain. No studies have so far tested the effect of human-robot emotional touch on experimentally induced pain ratings, on mood and on oxytocin levels in healthy young adults. Here, we assessed the effect of touching the robot PARO on pain perception, on mood and on salivary oxytocin levels, in 83 young adults. We measured their perceived pain, happiness state, and salivary oxytocin. For the 63 participants in the PARO group, pain was assessed in three conditions: Baseline, Touch (touching PARO) and No-Touch (PARO present). The control group (20 participants) underwent the same measurements without ever encountering PARO. There was a decrease in pain ratings and in oxytocin levels and an increase in happiness ratings compared to baseline only in the PARO group. The Touch condition yielded a larger decrease in pain ratings compared to No-Touch. These effects correlated with the participants’ positive perceptions of the interaction with PARO. Participants with higher perceived ability to communicate with PARO experienced a greater hypoalgesic effect when touching PARO. We show that human-robot social touch is effective in reducing pain ratings, improving mood and - surprisingly - reducing salivary oxytocin levels in adults.

Social interaction is one of the most basic survival needs of humans1. Both in childhood2,3,4,5 and in older ages6,7,8, the impact of social connections on health seems to be crucial. For example, poor social relationships and social isolation were associated with high incidence of general morbidity9,10, stress disorders11,12 and chronic pain11,13,14. Close relationships, however, were found to be a protective factor against stress and pain disorders15,16,17,18. Close interpersonal relationships often involve emotional touch, which may act as a mediating factor in the effect of social relationships on pain relief. Emotional touch is defined as a pleasant touch between two humans19. Emotional touch may include active touching (i.e. stroking another person), passive touching (being touched by another person) or dyadic touching (i.e. hand holding)20,21. Indeed, several studies have found that handholding22 and hugging23 reduce the physiological and psychological response to stress among men and women. It was suggested that empathic abilities of both the person touching and the person touched play a fundamental role in this effect24. Emotional touch also stimulates the hypothalamic-pituitary system to secrete oxytocin20,25, a hormone that has been characterized as having a central role in mediating feelings of love, social attachment and communication in both animals and humans26,27,28,29. In an animal study, there was an increase in pain thresholds following petting, as well as following injection of oxytocin. In both situations (petting or injection of oxytocin), the effect on the pain threshold disappeared with the administration of an oxytocin antagonist30. Similarly, in humans, Kreuder et al.31, recently demonstrated that administration of nasal oxytocin enhances the pain-relieving effects of social support in romantic couples. In addition, it was found that being touched by another person32 and handholding with a spouse33,34 induce a reduction in pain ratings among women. The level of the analgesic effect when holding a partner’s hand was associated with the toucher’s empathic tendencies33. These studies suggest that emotional touch may lead to decreased sensitivity to pain that may be associated with the release of oxytocin. How, then, can the beneficial effect of emotional touch on the perception of pain be provided to individuals who do not have access to it? One way to fill this need may be through a social robot. A social robot may take on a human-like35,36 or a pet-like appearance, or move like one e.g37,38.. It is designed to create social relationships with people39 for either entertainment40, education41, or for therapeutic purposes42,43. Shibata44 developed a seal-like robot named PARO designed to elicit a feeling of social connection. Interaction with PARO was found to improve mood45,46, and to reduce stress and anxiety of older people, and of individuals with dementia45,46,47, as well as to improve the mood of pediatric patients48. In one study, participants interacted with PARO for the duration of one year, during which the effects on mood were maintained46. In addition, interaction with PARO49 and with a humanoid robot50 was found to reduce stress, anxiety and pain levels during medical procedures (chemotherapy among women and vaccination among children, respectively). However, a recent review concluded that better methodology and measures are needed to draw conclusions about the effect of human-robot social interactions on pain51. Indeed, no controlled studies specifically examined the effect of the robot’s touch as opposed to the robot’s presence, without any physical contact, on the perception of pain. In addition, no controlled studies have examined the effect of human-robot social interaction on either oxytocin secretion or on experimentally induced pain ratings.

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