The Effects of Intranasal Oxytocin on Neural and Behavioral Responses to Social Touch in the Form of Massage

Subcutaneous Oxytocin Injection Reduces Heat Pain: A Randomized-Controlled Trial

Oxytocin (OT) is a neuropeptide broadly implicated in social relationships and behavior. OT also exerts antinociceptive and pain-reducing effects in both humans and rodents. Recent research in rodents demonstrates that these effects can be peripheral and local. In human studies, intravenous OT has reduced visceral pain, and subcutaneous injection of OT has reduced postsurgical pain. However, the local effects of subcutaneous OT on experimental pain have not been studied. We conducted a 2-session crossover study during which healthy adults received a subcutaneous injection of synthetic OT (4 mcg/2 mL) or saline placebo (isotonic saline 2 mL), in a randomized and double-blinded manner. Eighteen participants completed full study procedures. We hypothesized that 10 minutes after injection, OT would reduce measures of acute mechanical pain, pressure pain, and heat pain perception. Subcutaneous OT significantly reduced ratings of heat pain intensity and unpleasantness (both P < .01), but did not alter mechanical pain, pressure pain, or heat pain threshold (all P > .05). Changes in heat pain were observed only on the injected arm and not on the contralateral arm, confirming a localized mechanism. These findings confirm the ability of OT in or near the skin to modulate nociceptive processes in cutaneous tissues in human adults, opening exciting avenues for further mechanistic research as well as potential clinical applications for acute pain. PERSPECTIVE: This randomized-controlled trial showed that a subcutaneous injection of OT could reduce perception of heat pain tested with a thermode. OT did not alter mechanical or pressure pain or thresholds for perceiving heat pain. These findings are relevant to scientists and clinicians seeking nonaddictive local drug treatments for pain.

Out of touch? How trauma shapes the experience of social touch - Neural and endocrine pathways

Trauma can shape the way an individual experiences the world and interacts with other people. Touch is a key component of social interactions, but surprisingly little is known about how trauma exposure influences the processing of social touch. In this review, we examine possible neurobiological pathways through which trauma can influence touch processing and lead to touch aversion and avoidance in trauma-exposed individuals. Emerging evidence indicates that trauma may affect sensory touch thresholds by modulating activity in the primary sensory cortex and posterior insula. Disturbances in multisensory integration and oxytocin reactivity combined with diminished reward-related and anxiolytic responses may induce a bias towards negative appraisal of touch contexts. Furthermore, hippocampus deactivation during social touch may reflect a dissociative state. These changes depend not only on the type and severity of the trauma but also on the features of the touch. We hypothesise that disrupted touch processing may impair social interactions and confer elevated risk for future stress-related disorders.

Role of medial prefrontal cortex and primary somatosensory cortex in self and other-directed vicarious social touch: a TMS study

Conflicting evidence points to the contribution of several key nodes of the 'social brain' to the processing of both discriminatory and affective qualities of interpersonal touch. Whether the primary somatosensory cortex (S1) and the medial prefrontal cortex (mPFC), two brain areas vital for tactile mirroring and affective mentalizing, play a functional role in shared representations of C-tactile (CT) targeted affective touch is still a matter of debate. Here, we used offline continuous theta-burst transcranial magnetic stimulation (cTBS) to mPFC, S1 and vertex (control) prior to participants providing ratings of vicarious touch pleasantness for self and others delivered across several body sites at CT-targeted velocities. We found that S1-cTBS led to a significant increase in touch ratings to the self, with this effect being positively associated to levels of interoceptive awareness. Conversely, mPFC-cTBS reduced pleasantness ratings for touch to another person. These effects were not specific for CT-optimal (slow) stroking velocities, but rather they applied to all types of social touch. Overall, our findings challenge the causal role of the S1 and mPFC in vicarious affective touch and suggest that self- vs other-directed vicarious touch responses might crucially depend on the specific involvement of key social networks in gentle tactile interactions.

Affective touch in the context of development, oxytocin signaling, and autism

Touch represents one of our most important senses throughout life and particularly in the context of our social and emotional experiences. In this review, we draw on research on touch processing from both animal models and humans. Firstly, we briefly describe the cutaneous touch receptors and neural processing of both affective and discriminative touch. We then outline how our sense of touch develops and summarize increasing evidence demonstrating how essential early tactile stimulation is for the development of brain and behavior, with a particular focus on effects of tactile stimulation in infant animals and pediatric massage and Kangaroo care in human infants. Next, the potential mechanisms whereby early tactile stimulation influences both brain and behavioral development are discussed, focusing on its ability to promote neural plasticity changes and brain interhemispheric communication, development of social behavior and bonding, and reward sensitivity through modulation of growth factor, oxytocin, and opioid signaling. Finally, we consider the implications of evidence for atypical responses to touch in neurodevelopmental disorders such as autism spectrum disorder and discuss existing evidence and future priorities for establishing potential beneficial effects of interventions using massage or pharmacological treatments targeting oxytocin or other neurochemical systems.

Oxytocin Reduces the Attractiveness of Silver-Tongued Men for Women During Mid-Cycle

In humans, the neuropeptide oxytocin promotes both attraction toward and bonds with romantic partners, although no studies have investigated whether this extends to the perceived attractiveness of flirtatious language. In a within-subject, randomized double-blind placebo-controlled behavior and functional magnetic resonance imaging (fMRI) paradigm (https://clinicaltrials.gov/show/NCT03144115), 75 women rated the attractiveness of either a male face alone or paired with a verbal compliment which varied in terms of topic (women or landscapes) and figurativeness (novel or conventional metaphors or literal expressions). Subjects were tested in fertile and luteal phases of their cycle and on both occasions received either 24 IU intranasal oxytocin or placebo. Results showed that, whereas under placebo women in the fertile phase rated the facial attractiveness of men producing novel metaphorical compliments higher than in their luteal phase, following oxytocin treatment they did not. Correspondingly, under oxytocin the faces of individuals producing novel metaphorical compliments evoked greater responses in brain regions involved in processing language (middle frontal gyrus) and cognitive and emotional conflict (posterior middle cingulate and dorsal anterior cingulate) but reduced functional connectivity between the dorsal anterior cingulate and right orbitofrontal and medial frontal gyri. Thus, sex hormones and oxytocin may have opposite effects in regulating mate selection in women during their fertile phase. Novel metaphorical compliments convey a greater sexual than bonding intention and thus while sex hormones at mid-cycle may promote attraction to individuals communicating sexual rather than bonding intent, oxytocin may bias attraction away from such individuals through increasing cognitive and emotional conflict responses toward them.

Early Postpartum Maternal and Newborn Responses to Auditory, Tactile, Visual, Vestibular, and Olfactory Stimuli

OBJECTIVE

To compare maternal psychological well-being, newborn behavior, and maternal and newborn salivary oxytocin (OT) and cortisol before and after two maternally administered multisensory behavioral interventions or an attention control group.

DESIGN

Randomized prospective clinical trial.

SETTING

U.S. Midwest community hospital.

PARTICIPANTS

Newborns and their mothers (n = 102 dyads) participated. Mothers gave birth vaginally at term gestation and had no physical or mental health diagnoses. Newborns with low Apgar scores, receipt of oxygen, suspected infection, or congenital anomalies were excluded.

METHODS

Dyads were randomly assigned to the auditory, tactile, visual, and vestibular (ATVV) intervention, the ATVV with odor from a baby lotion (ATVVO), or the attention control (AC) Group. Maternal psychological well-being, newborn behavior, and endocrine responses (salivary cortisol and OT) were measured before and after the intervention.

RESULTS

Newborns in the ATVV and ATVVO groups exhibited increases in potent engagement behaviors (p < .0001 and p = .001, respectively). Newborns in the AC group exhibited a decrease in potent engagement (p = .013) and an increase in potent disengagement (p = .029). Mothers in the ATVVO group exhibited an increase in OT (p = .01) and the largest change in OT (p = .02) compared to mothers in the ATVV and AC groups. We noted no change in maternal psychological well-being or newborn endocrine responses.

CONCLUSION

Inclusion of an odor via lotion with a behavioral intervention (ATVV) influenced maternal OT more than the behavioral intervention alone. Newborns were behaviorally responsive to the interventions; however, endocrine measures were not associated with intervention changes.

The role of the amygdala in processing social and affective touch

The amygdala plays a central role in emotion and social behavior, yet its role in processing social and affective touch is not well established. Longitudinal studies reveal that touch-deprived infants show later in life exaggerated emotional reactivity related to structural and functional changes in the amygdala and other brain structures. The internal organization and connectivity of the amygdala is well-suited to process the sensory features of tactile stimuli and also the socio-cognitive dimensions of the received touch. The convergent processing of bottom-up and top-down pathways that carry information about touch results in the elaboration of context appropriate autonomic responses. Indeed, the positive value of affective touch in humans and social grooming in non-human primates is correlated with vagal tone and the release of oxytocin and endogenous opioids. Grooming, the non-human primate equivalent of affective touch in humans, reduces vigilance, that depends on the amygdala. During touch-induced vagal tone and low vigilance, neural activity in the amygdala is substantially different from activity corresponding to the attentive processing of tactile stimuli. Under these circumstances neurons no longer respond phasically to each touch stimulus, rather they signal a sustained functional state in which the amygdala appears decoupled from monitoring the external environment.

Neural Functions of Hypothalamic Oxytocin and its Regulation

Oxytocin (OT), a nonapeptide, has a variety of functions. Despite extensive studies on OT over past decades, our understanding of its neural functions and their regulation remains incomplete. OT is mainly produced in OT neurons in the supraoptic nucleus (SON), paraventricular nucleus (PVN) and accessory nuclei between the SON and PVN. OT exerts neuromodulatory effects in the brain and spinal cord. While magnocellular OT neurons in the SON and PVN mainly innervate the pituitary and forebrain regions, and parvocellular OT neurons in the PVN innervate brainstem and spinal cord, the two sets of OT neurons have close interactions histologically and functionally. OT expression occurs at early life to promote mental and physical development, while its subsequent decrease in expression in later life stage accompanies aging and diseases. Adaptive changes in this OT system, however, take place under different conditions and upon the maturation of OT release machinery. OT can modulate social recognition and behaviors, learning and memory, emotion, reward, and other higher brain functions. OT also regulates eating and drinking, sleep and wakefulness, nociception and analgesia, sexual behavior, parturition, lactation and other instinctive behaviors. OT regulates the autonomic nervous system, and somatic and specialized senses. Notably, OT can have different modulatory effects on the same function under different conditions. Such divergence may derive from different neural connections, OT receptor gene dimorphism and methylation, and complex interactions with other hormones. In this review, brain functions of OT and their underlying neural mechanisms as well as the perspectives of their clinical usage are presented.

Oxytocin facilitates socially directed attention

Socially directed gaze following is an important component of social interaction and communication, allowing us to attend mutually with others to objects or people so that we can share their experience and also learn from them. This type of joint social attention is impaired in disorders such as autism. Previous research has demonstrated that the neuropeptide oxytocin can facilitate attention toward social cues, although to date no study in humans has investigated its influence on socially directed gaze or on associations of the latter with autistic and empathic traits. In a within-subject, randomized, placebo-controlled trial we used eye-tracking to investigate the effects of intranasal oxytocin (24 IU) on socially directed gaze toward one of two objects in 40 adult male subjects. Subjects viewed videos of an actor and actress directing their gaze toward one of two objects by either moving only their eyes, moving both their eyes and head, or moving their eyes and head and pointing with a finger. Results showed that OXT increased the proportion of time subjects viewed the object the actor or actress were looking/pointing at across all three conditions, although unexpectedly we found no associations with trait autism or empathy under either placebo or OXT treatments. These findings demonstrate that OXT can facilitate socially directed gaze following to promote mutual attention toward objects which may be potentially beneficial therapeutically in disorders with impaired social communication and interaction.