Effects of oxytocin on human social approach measured using intimacy equilibriums

Neuroimaging and behavioral evidence of sex-specific effects of oxytocin on human sociality

Although the social role of oxytocin came to light due to sex-specific interactions such as mother-offspring bonding, current understanding of sex differences in the effects of oxytocin on human sociality is limited because of the predominance of all-male samples. With the increasing inclusion of females in intranasal oxytocin research, it is now possible to explore such patterns. Neuroimaging studies reveal relatively consistent sex-differential effects of oxytocin on the activation of brain regions associated with processing social stimuli - particularly the amygdala. Findings from behavioral research are varied but suggest that oxytocin more often facilitates social cognition and positive social interactions in males, with context-dependent effects in each sex. We discuss potential biological and psychological mechanisms underlying the reported sex differences, and conclude with considerations for future research and clinical applications of oxytocin.

Closeness-inducing discussions with a romantic partner increase cortisol and testosterone

Despite progress in understanding the social neuroendocrinology of close relationship processes, most work has focused on negative experiences, such as relationship conflict or stress. As a result, much less is known about the neuroendocrine implications of positive, emotionally intimate relationship experiences. In the current study, we randomly assigned 105 dating or married couples to a 30-minute semi-structured discussion task that was designed to elicit either high or low levels of closeness. Participants provided pre- and post-task saliva samples (to assess cortisol and testosterone) and post-task reports of self-disclosure, closeness, attraction, positive and negative affect, and stress. Participants found the discussion conditions comparably positive and enjoyable, but those in the high-closeness condition reported that they disclosed marginally more and felt marginally closer to their partners than those in the low-closeness condition. Participants also showed larger increases in cortisol and testosterone during the high (versus low) closeness discussion, and self-reported disclosure mediated these increases in cortisol and testosterone. Self-reported closeness and other theoretically plausible mediators, such as sexual attraction and excitement, did not mediate changes in either hormone. Taken together, the current findings contribute to our understanding of neuroendocrine changes associated with emotionally intimate relationship experiences. We consider possible explanations for the hormone changes we observed and offer directions for future research on the neuroendocrine implications of close relationship experiences.

Intranasal oxytocin decreases self-oriented learning

RATIONALE

Oxytocin has been found to play an important role in human social cognition and social interaction. Over the last two decades, surge studies have been conducted to investigate how oxytocin impacts other-oriented processes, such as trust and generosity (Zak et al. in PLoS ONE 2(11):e1128, 2007); however, the examination of the effect of oxytocin on self-related processes was relatively inadequate. Appropriate and efficient social interactions require both self- and other-related information processing. Recent studies have found that intranasal oxytocin (IN-OT) influences the self-related process, although the results have been mixed. The computational process underlying the effects of IN-OT on self-processing remains unknown.

OBJECTIVES

We aim to investigate the effect of IN-OT on self-oriented learning across different contexts (self-other independent vs. self-other dependent) and uncover the process by which IN-OT affects dynamic behavior changes.

METHODS

We performed two double-blind, placebo-controlled studies and used reinforcement learning theory to integrate action and related feedback for participants' behaviors.

RESULTS

In study 1, IN-OT decreased self-oriented reward learning when self-oriented learning and prosocial (other-oriented) learning were assessed separately. These effects were partially due to the OT-related increase in choice variability during self-oriented learning. In study 2, IN-OT also decreased learning performance during self-oriented reward learning when self-related and other-related rewards were present together. These effects occurred at an early stage of the learning process and could be moderated by the participants' social value orientation. Our findings show that OT attenuates the process of self-oriented learning and provides an underlying computational process.

CONCLUSIONS

Our findings shed new light on the dynamics of IN-OT's effects on human self-oriented learning processes. For future studies on OT effects on self-oriented learning, individual factors such as social value orientation should be taken into consideration in research development and analysis.

Relevance of number and physiological status of conspecifics in preventing stress-induced decreases in newly proliferated cells and neuroblasts

RATIONALE AND OBJECTIVE

The presence of three conspecifics prevents stress-induced decreases in newly proliferated cells and neuroblasts in mouse dentate gyrus (DG). In this study, we sought to determine how many conspecifics are required to exert these protective effects against stress. In addition, we manipulated the physiological status of those conspecifics in the context of their stress-buffering effects and used airborne oxytocin exposure as a substitute for the presence of conspecifics.

MATERIALS AND METHODS

Bromodeoxyuridine staining was used to indicate the newly proliferated cells and co-staining with doublecortin to reveal the proliferative neuroblasts.

RESULTS

Presentation of three intact and lipopolysaccharide-treated conspecifics prevented the stress-induced decreases in the number of newly proliferated cells and neuroblasts in DG. Presentation of one saline- or oxytocin (OT)-treated conspecific did not exert observable stress-buffering effects. In contrast, airborne oxytocin prevented the stress-induced decreases in DG cell proliferation and early neurogenesis, while pretreatment with L-371,257, a selective OT receptor antagonist, abolished the buffering effects of OT.

CONCLUSIONS

Physical interaction with the conspecifics and conspecifics' sickness, at best, play a minor role in mediating the buffering effects against stress-induced decreases in DG cell proliferation or early neurogenesis. Moreover, stress-buffering effects are negligible with the presence of only one conspecific. Finally, airborne OT produced stress-buffering effects possibly via its stimulation of OT receptors. Oxytocin merits further study as a substitute for the stress-buffering effects of companions.

Oxytocin attenuates social and non-social avoidance: Re-thinking the social specificity of Oxytocin

Re-examining decades of the social construal of Oxytocin, the General Approach-Avoidance Hypothesis of Oxytocin (GAAO) predicts that Oxytocin will modulate responding to emotionally-evocative and personally-relevant social and non-social stimuli due to its action on the neural substrate of approach and avoidance motivation. We report the first critical experimental test of GAAO predictions by means of a double-blind intra-nasal administration of Oxytocin vs. placebo in 90 healthy adults (N=90, 50% women). As predicted, we found that among men and women for whom negative emotion (anxious arousal) is motivationally-relevant, intra-nasal administration of Oxytocin reduced behavioral avoidance of emotionally-evocative negatively-valenced social and non-social stimuli, but not closely matched emotionally-neutral stimuli. Findings cannot be explained by extant social theories of Oxytocin. We discuss the implications of the present findings for basic and translational clinical Oxytocin research.

The role of oxytocin in modulating interpersonal space: A pharmacological fMRI study

Interpersonal space is a nonverbal indicator of affiliation and closeness. In this study we investigated the effects of oxytocin (OT), a neuropeptide known for its social role in humans, on interpersonal space. In a double blind placebo controlled study we measured the effect of intranasal OT on the personal distance preferences of different familiar (friend) and unfamiliar (stranger) protagonists. Behavioral results showed that participants preferred to be closer to a friend than to a stranger. Intranasal OT was associated with an overall distancing effect, but this effect was significant for the stranger and not for the friend. The imaging results showed interactions between treatment (OT, placebo) and protagonist (friend, stranger) in regions that mediate social behavior including the dorsomedial prefrontal cortex (dmPFC), a region associated with the mentalizing system. Specifically, OT increased activity in the dmPFC when a friend approached the participants but not when a stranger approached. The results indicate that the effect of OT on interpersonal space greatly depends on the participant's relationship with the protagonist. This supports the social salience theory, according to which OT increases the salience of social cues depending on the context.

A general approach-avoidance hypothesis of oxytocin: accounting for social and non-social effects of oxytocin

BACKGROUND

We critically reexamine extant theory and empirical study of Oxytocin. We question whether OT is, in fact, a "social neuropeptide" as argued in dominant theories of OT.

METHOD

We critically review human and animal research on the social and non-social effects of Oxytocin, including behavioral, psychophysiological, neurobiological, and neuroimaging studies.

RESULTS

We find that extant (social) theories of Oxytocin do not account for well-documented non-social effects of Oxytocin. Furthermore, we find a range of evidence that social and non-social effects of Oxytocin may be mediated by core approach-avoidance motivational processes.

CONCLUSIONS

We propose a General Approach-avoidance Hypothesis of Oxytocin (GAAO). We argue that the GAAO may provide a parsimonious account of established social and non-social effects of Oxytocin. We thus re-conceptualize the basic function(s) and mechanism(s) of action of Oxytocin. Finally, we highlight implications of the GAAO for basic and clinical research in humans

Hormones as "difference makers" in cognitive and socioemotional aging processes

Aging is associated with well-recognized alterations in brain function, some of which are reflected in cognitive decline. While less appreciated, there is also considerable evidence of socioemotional changes later in life, some of which are beneficial. In this review, we examine age-related changes and individual differences in four neuroendocrine systems-cortisol, estrogen, testosterone, and oxytocin-as "difference makers" in these processes. This suite of interrelated hormonal systems actively coordinates regulatory processes in brain and behavior throughout development, and their level and function fluctuate during the aging process. Despite these facts, their specific impact in cognitive and socioemotional aging has received relatively limited study. It is known that chronically elevated levels of the stress hormone cortisol exert neurotoxic effects on the aging brain with negative impacts on cognition and socioemotional functioning. In contrast, the sex hormones estrogen and testosterone appear to have neuroprotective effects in cognitive aging, but may decrease prosociality. Higher levels of the neuropeptide oxytocin benefit socioemotional functioning, but little is known about the effects of oxytocin on cognition or about age-related changes in the oxytocin system. In this paper, we will review the role of these hormones in the context of cognitive and socioemotional aging. In particular, we address the aforementioned gap in the literature by: (1) examining both singular actions and interrelations of these four hormonal systems; (2) exploring their correlations and causal relationships with aspects of cognitive and socioemotional aging; and (3) considering multilevel internal and external influences on these hormone systems within the framework of explanatory pluralism. We conclude with a discussion of promising future research directions.

Social bonding: regulation by neuropeptides

Affiliative social relationships (e.g., among spouses, family members, and friends) play an essential role in human society. These relationships affect psychological, physiological, and behavioral functions. As positive and enduring bonds are critical for the overall well-being of humans, it is not surprising that considerable effort has been made to study the neurobiological mechanisms that underlie social bonding behaviors. The present review details the involvement of the nonapeptides, oxytocin (OT), and arginine vasopressin (AVP), in the regulation of social bonding in mammals including humans. In particular, we will discuss the role of OT and AVP in the formation of social bonds between partners of a mating pair as well as between parents and their offspring. Furthermore, the role of OT and AVP in the formation of interpersonal bonding involving trust is also discussed.

Oxytocin facilitates social approach behavior in women

In challenging environments including both numerous threats and scarce resources, the survival of an organism depends on its ability to quickly escape from dangers and to seize opportunities to gain rewards. The phylogenetically ancient neurohormonal oxytocin (OXT) system has been shown to influence both approach and avoidance (AA) behavior in men, but evidence for comparable effects in women is still lacking. We thus conducted a series of pharmacological behavioral experiments in a randomized double-blind study involving 76 healthy heterosexual women treated with either OXT (24 IU) or placebo intranasally. In Experiment 1, we tested how OXT influenced the social distance subjects maintained between themselves and either a female or male experimenter. In Experiment 2, we applied a reaction time based AA task. In Experiment 3 we investigated effects on peri-personal space by measuring the lateral attentional bias in a line bisection task. We found that OXT specifically decreased the distance maintained between subjects and the male but not the female experimenter and also accelerated approach toward pleasant social stimuli in the AA task. However, OXT did not influence the size of peri-personal space, suggesting that it does not alter perception of personal space per se, but rather that a social element is necessary for OXT's effects on AA behavior to become evident. Taken together, our results point to an evolutionarily adaptive mechanism by which OXT in women selectively promotes approach behavior in positive social contexts.

Oxytocin receptor gene polymorphisms are associated with human directed social behavior in dogs (Canis familiaris)

The oxytocin system has a crucial role in human sociality; several results prove that polymorphisms of the oxytocin receptor gene are related to complex social behaviors in humans. Dogs' parallel evolution with humans and their adaptation to the human environment has made them a useful species to model human social interactions. Previous research indicates that dogs are eligible models for behavioral genetic research, as well. Based on these previous findings, our research investigated associations between human directed social behaviors and two newly described (-212AG, 19131AG) and one known (rs8679684) single nucleotide polymorphisms (SNPs) in the regulatory regions (5' and 3' UTR) of the oxytocin receptor gene in German Shepherd (N = 104) and Border Collie (N = 103) dogs. Dogs' behavior traits have been estimated in a newly developed test series consisting of five episodes: Greeting by a stranger, Separation from the owner, Problem solving, Threatening approach, Hiding of the owner. Buccal samples were collected and DNA was isolated using standard protocols. SNPs in the 3' and 5' UTR regions were analyzed by polymerase chain reaction based techniques followed by subsequent electrophoresis analysis. The gene-behavior association analysis suggests that oxytocin receptor gene polymorphisms have an impact in both breeds on (i) proximity seeking towards an unfamiliar person, as well as their owner, and on (ii) how friendly dogs behave towards strangers, although the mediating molecular regulatory mechanisms are yet unknown. Based on these results, we conclude that similarly to humans, the social behavior of dogs towards humans is influenced by the oxytocin system.

Deconstructing sociality, social evolution and relevant nonapeptide functions

Although behavioral neuroendocrinologists often discuss "sociality" as a unitary variable, the term encompasses a wide diversity of behaviors that do not evolve in a linked fashion across species. Thus grouping, monogamy, paternal care, cooperative breeding/alloparental care, and various other forms of social contact are evolutionarily labile and evolve in an almost cafeteria-like fashion, indicating that relevant neural mechanisms are at least partially dissociable. This poses a challenge for the study of the nonapeptides (vasopressin, oxytocin, and homologous neuropeptides), because nonapeptides are known to modulate all of these aspects of sociality in one species or another. Hence, we may expect substantial diversity in the behavioral functions of nonapeptides across species, and indeed this is the case. Further compounding this complexity is the fact that the pleiotropic contributions of nonapeptides to social behavior are matched by pleiotropic contributions to physiology. Given these considerations, single "model systems" approaches to nonapeptide function will likely not have strong predictive validity for humans or other species. Rather, if we are to achieve predictive validity, we must sample a wide diversity of species in an attempt to derive general principles. In the present review, I discuss what is known about functional evolution of nonapeptide systems, and critically evaluate general assumptions about bonding and other functions that are based on the model systems approach. From this analysis I attempt to summarize what can and cannot be generalized across species, and highlight critical gaps in our knowledge about the functional evolution of nonapeptide systems as it relates to dimensions of sociality.

Helping oxytocin deliver: considerations in the development of oxytocin-based therapeutics for brain disorders

Concerns regarding a drought in psychopharmacology have risen from many quarters. From one perspective, the wellspring of bedrock medications for anxiety disorders, depression, and schizophrenia was serendipitously discovered over 30 year ago, the swell of pharmaceutical investment in drug discovery has receded, and the pipeline's flow of medications with unique mechanisms of action (i.e., glutamatergic agents, CRF antagonists) has slowed to a trickle. Might oxytocin (OT)-based therapeutics be an oasis? Though a large basic science literature and a slowly increasing number of studies in human diseases support this hope, the bulk of extant OT studies in humans are single-dose studies on normals, and do not directly relate to improvements in human brain-based diseases. Instead, these studies have left us with a field pregnant with therapeutic possibilities, but barren of definitive treatments. In this clinically oriented review, we discuss the extant OT literature with an eye toward helping OT deliver on its promise as a therapeutic agent. To this end, we identify 10 key questions that we believe future OT research should address. From this overview, several conclusions are clear: (1) the OT system represents an extremely promising target for novel CNS drug development; (2) there is a pressing need for rigorous, randomized controlled clinical trials targeting actual patients; and (3) in order to inform the design and execution of these vital trials, we need further translational studies addressing the questions posed in this review. Looking forward, we extend a cautious hope that the next decade of OT research will birth OT-targeted treatments that can truly deliver on this system's therapeutic potential.

A direct examination of the effect of intranasal administration of oxytocin on approach-avoidance motor responses to emotional stimuli

Oxytocin has been shown to promote a host of social behaviors in humans but the exact mechanisms by which it exerts its effects are unspecified. One prominent theory suggests that oxytocin increases approach and decreases avoidance to social stimuli. Another dominant theory posits that oxytocin increases the salience of social stimuli. Herein, we report a direct test of these hypotheses. In a double-blind, placebo-controlled study we examined approach-avoidance motor responses to social and non-social emotional stimuli. One hundred and twenty participants self-administered either 24 IU oxytocin or placebo and moved a lever toward or away from pictures of faces depicting emotional expressions or from natural scenes appearing before them on a computer screen. Lever movements toward stimuli decreased and movements away increased stimuli size producing the illusion that stimuli moved away from or approached participants. Reaction time data were recorded. The task produced the effects that were anticipated on the basis of the approach-avoidance literature in relation to emotional stimuli, yet the anticipated speeded approach and slowed avoidance responses to emotional faces by the oxytocin group were not observed. Interestingly, the oxytocin treatment group was faster to approach and avoid faces depicting disgust relative to the placebo group, suggesting a salience of disgust for the former group. Results also showed that within the oxytocin group women's reaction times to all emotional faces were faster than those of men, suggesting sex specific effects of oxytocin. The present findings provide the first direct evidence that intranasal oxytocin administration does not enhance approach/avoidance to social stimuli and does not exert a stronger effect on social vs. non-social stimuli in the context of processing of emotional expressions and scenes. Instead, our data suggest that oxytocin administration increases the salience of certain social stimuli and point to a possible role for oxytocin in behavioral prophylaxis.

Sex, receptors, and attachment: a review of individual factors influencing response to oxytocin

As discussed in the larger review in this special issue (MacDonald and Feifel), intranasal oxytocin (OT) is demonstrating a growing potential as a therapeutic agent in psychiatry. Importantly, research suggests that a variety of individual factors may influence a person's response to OT. In this mini-review, I provide a review of three: (1) sex and hormonal status; (2) genetic variation in aspects of the OT system (i.e., OT receptors); and (3) attachment history. Each of these factors will be important to monitor as we strive to develop a richer understanding of OT's role in human development, brain-based disease, and the potential for individualized, OT-targeted treatments.