Oxytocin release patterns and effects, with a focus on touch, social interaction, and closeness.

Clinical evidence indicates that tactile stimulation of the skin, such as stroking or gentle touch, elicits a range of beneficial physiological and psychological responses, such as increased social interaction, wellbeing, calm, restorative and growth promoting effects, as well as reduced fear, pain, and stress levels. These effects are mediated by activation of cutaneous sensory nerves, which relay signals to central regulatory systems. During this process, several neuropeptides and hormones are released, one of which is oxytocin produced in the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus. Oxytocin in turn stimulates social interaction, induces wellbeing and calm, and promotes growth and restorative processes in part via vagal activation of the endocrine system of the gastrointestinal tract and by inhibiting the activity within the hypothalamic pituitary adrenal (HPA)-axis and the sympathetic nervous system. It is proposed that cutaneous nerves are typically activated during social interaction through a two-step process. Gentle touch activates a two-neuron pathway involving tachykinin 1-neurons originating from the periaqueductal gray (PAG) and thereafter projecting to the SON and PVN. This activation triggers the release of oxytocin from neurons in the SON and PVN, which by activating oxytocin receptors promotes social interaction and rewarding mechanisms. Subsequent behaviors such as holding and caressing, trigger a second pool of cutaneous afferents, that respond to higher mechanical pressure than those triggered by gentle touch. We propose that these fibers are associated with oxytocin linked calming effects and with enhanced metabolic, restorative and growth promoting benefits, e.g., via vagal activation of the endocrine system of the gastrointestinal tract. In addition, anxiety, stress, pain and inflammation levels are decreased via oxytocinergic mechanisms in the brain. It is also possible that oxytocin released in response to cutaneous afferents exerts long-term effects by increasing oxytocin production and enhancing the function of oxytocin receptors. These two types of oxytocin-associated effect patterns may be activated, to varying degrees, in clinical practices involving skin-to-skin contact between individuals in certain therapeutic or caregiving contexts, such as skin-to-skin contact between infant and parent after birth or in the more long-term perspective during kangaroo care. Consequently, lack of social contact and closeness leads to reduced capacity for social interaction, increased stress levels, impaired health and even retarded growth at young age. Birth and breast-feeding, but not touch or closeness, are associated with a pulsatile release of oxytocin into the circulation. In addition, oxytocin linked pathways in the brain will be activated in response to birth and breastfeeding just as in response to touch and closeness. The release and effects of oxytocin will depend on the intensity and location of the cutaneous stimulation and of the oxytocin release pattern induced. Given the potential for different effects in response to distinct types of cutaneous stimulation manual therapies could be designed for targeted effects, such as reducing stress, relieving pain, boosting calm, or even promoting growth in early life. The aim of this narrative review was to explore the potential roles of central oxytocin, including its release and associated effects, in response to different types of sensory stimulation. In addition, we examine how oxytocin may contribute to social interaction and to clinical practices involving touch or close physical contact.