The neurobiology of pair bonding

The Influence of an Attachment-Related Stimulus on Oxytocin Reactivity in Poly-Drug Users Undergoing Maintenance Therapy Compared to Healthy Controls

BACKGROUND

Substance use disorders (SUDs) have been described as a dysfunctional way to compensate for deficiencies in that person's underlying attachment system. Furthermore, the neuropeptide oxytocin (OT), which is a critical component of the neurobiology of the attachment system, has been shown to effectively reduce addictive behavior and therefore has been discussed as a potential medication in SUD treatment. This study investigates variation in peripheral OT plasma levels as a function of exposure to an attachment-related stimulus in SUD patients compared to healthy controls (HCs).

METHODS

A total sample of 48 men, 24 inpatients in maintenance treatment who were diagnosed with poly-drug use disorder (PUD) and 24 HC, was investigated. A 15-min exposure to the Adult Attachment Projective Picture System (AAP) was used as an attachment-related stimulus and coded for attachment status. Blood samples before and after the AAP-assessment were taken and assayed for OT levels. Variation in baselines level of OT was examined in relation to the Alcohol, Smoking and Substance Involvement Screening Test (ASSIST), the Adult Attachment-Scale (AAS), and the Brief Symptom Inventory (BSI).

RESULTS

Following the AAP stimulus controls showed no significant difference in OT levels elevation from baseline compared to the PUD group's OT levels. Furthermore, in the PUD group only OT-baseline-levels may be negatively associated with the AAS subscale "Comfort with Closeness" and "Anxiety" and lifetime substance use.

DISCUSSION

Our results suggest that peripheral OT levels in poly-drug users undergoing maintenance treatment are not significantly different in responsiveness to an attachment related stimulus compared to HC. With regard to non-significant tendencies observed in this study which hint toward decreased OT-reactivity in the PUD group, further research is needed to explore this hypothesis with increased statistical power.

Social Games and Genic Selection Drive Mammalian Mating System Evolution and Speciation

Mating system theory based on economics of resource defense has been applied to describe social system diversity across taxa. Such models are generally successful but fail to account for stable mating systems across different environments or shifts in mating system without a change in ecological conditions. We propose an alternative approach to resource defense theory based on frequency-dependent competition among genetically determined alternative behavioral strategies characterizing many social systems (polygyny, monogamy, sneak). We modeled payoffs for competition, neighborhood choice, and paternal care to determine evolutionary transitions among mating systems. Our model predicts four stable outcomes driven by the balance between cooperative and agonistic behaviors: promiscuity (two or three strategies), polygyny, and monogamy. Phylogenetic analysis of 288 rodent species supports assumptions of our model and is consistent with patterns of evolutionarily stable states and mating system transitions. Support for model assumptions include that monogamy and polygyny evolve from promiscuity and that paternal care and monogamy are coadapted in rodents. As predicted by our model, monogamy and polygyny occur in sister taxa among rodents more often than by chance. Transitions to monogamy also favor higher speciation rates in subsequent lineages, relative to polygynous sister lineages. Taken together, our results suggest that genetically based neighborhood choice behavior and paternal care can drive transitions in mating system evolution. While our genic mating system theory could complement resource-based theory, it can explain mating system transitions regardless of resource distribution and provides alternative explanations, such as evolutionary inertia, when resource ecology and mating systems do not match.

The effect of individual and food characteristics on food retrieval and food sharing in captive Guinea baboons (Papio papio)

Access to food is of major importance to the fitness and survival of every individual, particularly in group-living animals, in which individual characteristics and food distribution can affect food intake. Additionally, several species of primates are known to share food under certain conditions. Such unresisted transfer of food from one individual to another appears to be adaptive, for instance as a tool to maintain and reinforce social bonds. In this study, we aimed to test how food retrieval and food sharing varies depending on the social relationship between individuals, and on the characteristics of the food. In six different test conditions, we provided a captive group of Guinea baboons (Papio papio, N = 23) with multiple food items, differing in quality, quantity, density, monopolizability, and effort required to obtain it. We further used behavioral observations to assess individual relationships and possible variations in grooming exchanges linked to food sharing events. Out of 424 events in which food items were retrieved by the subjects, we detected no instances of active food sharing and only 17 of passive food sharing. The way food was retrieved was affected by individual and food characteristics (i.e., quantity, quality, and monopolizability of food): Males and central individuals (i.e., those connected to many partners, and/or having partners with many connections in the social network) were more likely to retrieve food during test conditions. In particular, events of passive food sharing mostly happened when the quality of food was low, and between individuals belonging to the same community (i.e., having close relationships). No other food characteristics affected the probability to share food, and the occurrence of food sharing had no immediate effect on grooming exchanges. Overall, our findings suggest that food sharing is relatively rare in Guinea baboons unless the food has a low quality and individuals form close social bonds.

Endocrine Regulations in Human-Dog Coexistence through Domestication

Endocrine system regulation is important for the maintenance of homeostasis; it controls hormonal functions in complex physiology and behavior and adaptations to social environments. Evidence indicates that for more than 35 000 years, dogs (Canis familiaris) have been domesticated through living with humans. For example, they have acquired human-like social skills, such as eye gazing and pointing gestures. These unique behaviors are, at least partially, regulated by hormones and are thought to have been genetically altered throughout domestication. Glucocorticoids affect social tolerance, while oxytocin facilitates social coordination and familiarity between individuals. We review historical and recent literature to facilitate an understanding of the roles of glucocorticoid and oxytocin functions in the human-canine coexistence dynamic established during domestication.

Leu8 and Pro8 oxytocin agonism differs across human, macaque, and marmoset vasopressin 1a receptors

Oxytocin (OXT) is an important neuromodulator of social behaviors via activation of both oxytocin receptors (OXTR) and vasopressin (AVP) 1a receptors (AVPR1a). Marmosets are neotropical primates with a modified OXT ligand (Pro⁸-OXT), and this ligand shows significant coevolution with traits including social monogamy and litter size. Pro⁸-OXT produces more potent and efficacious responses at primate OXTR and stronger behavioral effects than the consensus mammalian OXT ligand (Leu⁸-OXT). Here, we tested whether OXT/AVP ligands show differential levels of crosstalk at primate AVPR1a. We measured binding affinities and Ca²⁺ signaling responses of AVP, Pro⁸-OXT and Leu⁸-OXT at human, macaque, and marmoset AVPR1a. We found that AVP binds with higher affinity than OXT across AVPR1a, and marmoset AVPR1a show a 10-fold lower OXT binding affinity compared to human and macaque AVPR1a. Both Leu⁸-OXT and Pro⁸-OXT produce a less efficacious response than AVP at human AVPR1a and higher efficacious response than AVP at marmoset AVPR1a. These data suggest that OXT might partially antagonize endogenous human AVPR1a signaling and enhance marmoset AVPR1a signaling. These findings aid in further understanding inconsistencies observed following systemic intranasal administration of OXT and provide important insights into taxon-specific differences in nonapeptide ligand/receptor coevolution and behavior.

Effect of Canine Oxytocin Receptor Gene Polymorphism on the Successful Training of Drug Detection Dogs

Drug detection dogs can be trained to locate various prohibited drugs with targeted odors, and they play an important role in the interdiction of drug smuggling in human society. Recent studies provide the interesting hypothesis that the oxytocin system serves as a biological basis for co-evolution between dogs and humans. Here, we offer the new possibility that genetic variation of the canine oxytocin receptor (OXTR) gene may regulate the success of a dog's training to become a drug detection dog. A total of 340 Labrador Retriever dogs that were trained to be drug detection dogs in Japan were analyzed. We genotyped an exonic SNP (rs8679682) in the OXTR gene and compared the training success rate of dogs with different genotypes. We also asked dog trainers in the training facility to evaluate subjective personality assessment scores for each dog and examined how each dog's training success was related to those scores. A significant effect of the OXTR genotype on the success of the dogs' training was found, with a higher proportion of dogs carrying the C allele (T/C and C/C genotypes) being successful candidates than dogs carrying the T/T genotype. Dog personality scores of Training Focus (Factor 1) were positively correlated with an increased likelihood that a dog would successfully complete training. Although the molecular mechanism of the OXTR gene and its functional pathway related to dog behavior remains unknown, our findings suggest that canine OXTR gene variants may regulate individual differences between dogs in their responsiveness to training for drug detection.

The inflammatory event of birth: How oxytocin signaling may guide the development of the brain and gastrointestinal system

The role of oxytocin (OT) as a neuropeptide that modulates social behavior has been extensively studied and reviewed, but beyond these functions, OT's adaptive functions at birth are quite numerous, as OT coordinates many physiological processes in the mother and fetus to ensure a successful delivery. In this review we explore in detail the potential adaptive roles of oxytocin as an anti-inflammatory, protective molecule at birth for the developing fetal brain and gastrointestinal system based on evidence that birth is a potent inflammatory/immune event. We discuss data with relevance for a number of neurodevelopmental disorders, as well as the emerging role of the gut-brain axis for health and disease. Finally, we discuss the potential relevance of sex differences in OT signaling present at birth in the increased male vulnerability to neurodevelopmental disabilities.

Circuits for social learning: A unified model and application to Autism Spectrum Disorder

Early life social experiences shape neural pathways in infants to develop lifelong social skills. This review presents the first unified circuit-based model of social learning that can be applied to early life social development, drawing together unique human developmental milestones, sensitive learning periods, and behavioral and neural scaffolds. Circuit domains for social learning are identified governing Activation, Integration, Discrimination, Response and Reward (AIDRR) to sculpt and drive human social learning. This unified model can be used to identify social delays earlier in development. We propose social impairments observed in Autism Spectrum Disorder are underpinned by early mistimed sensitive periods in brain development and alterations in amygdala development to disrupt the AIDRR circuits. This model directs how interventions can target neural circuits for social development and be applied early in life. To illustrate, the role of oxytocin and its use as an intervention is explored. The AIDRR model shifts focus away from delivering broad treatments based only on diagnostic classifications, to specifying and targeting the relevant circuits, at the right time of development, to optimize social learning.

Evaluating the stability of individual variation in social and nonsocial behavioural types using prairie voles (Microtus ochrogaster)

Prairie voles (Microtus ochrogaster) exhibit remarkable individual variation in social behaviour, suggesting differences in behavioural types. To date, however, there has been little assessment of whether these behavioural types are stable across test sessions, nor to what extent internal states and external contexts (domains) drive individual differences. Here we examined the individual consistency of social (huddling) and non-social (distance moved) behaviour across repeated, long-duration tests, in same-sex cagemate (SS-CM), same-sex stranger (SS-S), opposite-sex stranger (OS-S), and standard partner preference test (PPT) contexts. The SS-CM and SS-S tests were repeated multiple times (SS-CM 1-2; SS-S 1-5) to assess state-dependent variation. A second cohort was used to determine the replicability of findings. Overall, there was a general lack of stability in huddling behavior. It was inconsistent across repeated sessions of the same test type and between types of tests, suggesting a strong contribution of state-dependent variation. Non-social behaviour was more consistent and appeared more domain-dependent and less state-dependent than huddling. Translational and comparative studies of individual variation would likely benefit from testing across multiple contexts and employing repetitive testing paradigms to account for state-dependent variation.

Trust Games and Beyond

Trust is fundamental for the stability of human society. A large part of the experimental literature relies on the Trust Game as the workhorse to measure individual differences in trust and trustworthiness. In this review we highlight the difficulties and limitations of this popular paradigm, as well as the relations to alternative instruments ranging from survey measures to neurochemical manipulations and neuroimaging.

It takes two! Exploring sex differences in parenting neurobiology and behaviour

Parents lay the foundation for their children's socio-emotional experiences by sensitively responding to their needs. The hormonal and neurobiological changes that occur during the transition to parenthood importantly contribute to the parents' caregiving behaviour toward their children. Much research has emphasised the relationship between the mother, who is most often the primary caregiver, and her infant, with less focus on the role of fathers in child development. However, recent accounts have suggested that fathers also play an important role in promoting the health, development and psychosocial wellbeing of their children. Evidence from the behavioural literature has indicated that there are significant differences between typical mother-infant versus father-infant interactions. The current review aims to outline differences between maternal and paternal caregiving by discussing the differences in their biological mechanisms. First, we focus on the different hormones that are correlated with sensitive parenting behaviours in mothers and fathers. Next, we discuss the differences between neural bases of motherhood and fatherhood. Lastly, we discuss ways in which parental hormones, parental brain and parental exposure to infant cues interact to shape parental caregiving behaviour. In summary, this review highlights the distinct but complementary nature of maternal and paternal caregiving.

The neural mechanisms and circuitry of the pair bond

Love is one of our most powerful emotions, inspiring some of the greatest art, literature and conquests of human history. Although aspects of love are surely unique to our species, human romantic relationships are displays of a mating system characterized by pair bonding, likely built on ancient foundational neural mechanisms governing individual recognition, social reward, territorial behaviour and maternal nurturing. Studies in monogamous prairie voles and mice have revealed precise neural mechanisms regulating processes essential for the pair bond. Here, we discuss current viewpoints on the biology underlying pair bond formation, its maintenance and associated behaviours from neural and evolutionary perspectives.

Generic Homo sapiens and Unique Mus musculus: Establishing the Typicality of the Modeled and the Model Species

The question of how complex human abilities evolved, such as language or face recognition, has been pursued by means of multiple strategies. Highly specialized non-human species have been examined analytically for formal similarities, close phylogenetic relatives have been examined for continuity, and simpler species have been analyzed for the broadest view of functional organization. All these strategies require empirical evidence of what is variable and predictable in both the modeled and the model species. Turning to humans, allometric analyses of the evolution of brain mass and brain components often return the interesting, but disappointing answer that volumetric organization of the human brain is highly predictable seen in its phylogenetic context. Reconciling this insight with unique human behavior, or any species-typical behavior, represents a serious challenge. Allometric analyses of the order and duration of mammalian neural development show that, while basic neural development in humans is allometrically predictable, conforming to adult neural architecture, some life history features deviate, notably that weaning is unusually early. Finally, unusual deviations in the retina and central auditory system in the laboratory mouse, which is widely assumed to be “generic,” as well as severe deviations from expected brain allometry in some mouse strains, underline the need for a deeper understanding of phylogenetic variability even in those systems believed to be best understood.

Sociability and pair-bonding in gerbils: a comparative experimental study

In a study of gerbils with contrasting social and mating systems (group-living monogamous Mongolian gerbil Meriones unguiculatus, solitary nonterritorial promiscuous midday jird M. meridianus, and solitary territorial promiscuous pale gerbil Gerbillus perpallidus), we employed partner preference tests (PPTs) to assess among-species variation in sociability and pair-bonding patterns and tested whether the nature of contact between individuals: direct contact (DC) versus nondirect contact (NDC) affected our results. We measured male preferences as the time: 1) spent alone, 2) with familiar (partner), and 3) unfamiliar (stranger) female in the 3-chambered apparatus. Gerbil species differed strongly in sociability and male partner preferences. The time spent alone was a reliable indicator of species sociability independent of the nature of contact, whereas the pattern and level of between-species differences in male partner preferences depended on contact type: DC PPTs, unlike NDC-tests, discriminated well between monogamous and promiscuous species. In the DC-tests, stranger-directed aggression and stranger avoidance were observed both in the highly social monogamous M. unguiculatus and the solitary territorial promiscuous G. perpallidus, but not in the nonterritorial promiscuous M. meridianus. In M. unguiculatus, stranger avoidance in the DC-tests increased the time spent with the partner, thus providing evidence of a partner preference that was not found in the NDC-tests, whereas in G. perpallidus, stranger avoidance increased the time spent alone. This first comparative experimental study of partner preferences in gerbils provides new insights into the interspecific variation in gerbil sociality and mating systems and sheds light on behavioral mechanisms underlying social fidelity and pair-bonding.

The influence of oxytocin and vasopressin on men's judgments of social dominance and trustworthiness: An fMRI study of neutral faces

Cues signaling trust and dominance are crucial for social life. Previous studies on the effects of oxytocin (OT) nasal sprays on trustworthiness evaluations have been inconsistent and its influence on dominance is unknown. Vasopressin (AVP) may also influence social cue perception, but even fewer investigations have evaluated this possibility. We evaluated the effects of intranasal OT and AVP compared to placebo control during three double-blinded functional magnetic resonance imaging sessions. Twenty males received a pseudo-randomized order of nasal spray conditions and rated the trustworthiness and dominance of neutral faces. OT increased facial dominance ratings compared to placebo. Neuroimaging results revealed an inverse relationship between brain activation and face ratings for OT compared to placebo in regions involved in processing emotional expressions. Specifically, the right superior temporal gyrus was attenuated as ratings increased and the left precuneus selectively diminished with increasing dominance ratings. Additionally, OT increased functional connectivity between frontoparietal regions and the right amygdala for faces rated as highly dominant, but OT increased connectivity between the fusiform gyrus, hippocampus, and bilateral ventral tegmental area (VTA) for faces perceived as highly trustworthy. Overall, OT increased the perception of dominance but did not influence trustworthiness judgments. However, we observed regional neural effects for OT that differed between judgments of trustworthiness and dominance. AVP attenuated left temporoparietal junction activity as face ratings increased, a result consistent with AVP influencing mentalization. AVP also led to increased left amygdala and right VTA connectivity with the putamen, which is consistent with cue-driven, habitual responses.

Emotional Contagion From Humans to Dogs Is Facilitated by Duration of Ownership

Emotional contagion is a primitive form of empathy that does not need higher psychological functions. Recent studies reported that emotional contagion exists not only between humans but also among various animal species. The dog (Canis familiaris) is a unique animal and the oldest domesticated species. Dogs have coexisted with humans for more than 30,000 years and are woven into human society as partners bonding with humans. Dogs have acquired human-like communication skills and, likely as a result of the domestication process, the ability to read human emotions; therefore, it is feasible that there may be emotional contagion between human and dogs. However, the higher time-resolution of measurement of emotional contagion between them is yet to be conducted. We assessed the emotional reactions of dogs and humans by heart rate variability (HRV), which reflects emotion, under a psychological stress condition on the owners. The correlation coefficients of heart beat (R-R) intervals (RRI), the standard deviations of all RR intervals (SDNN), and the square root of the mean of the sum of the square of differences between adjacent RR intervals (RMSSD) between dogs and owners were positively correlated with the duration of dog ownership. Dogs’ sex also influenced the correlation coefficients of the RRI, SDNN, and RMSSD in the control condition; female showed stronger values. These results suggest that emotional contagion from owner to dog can occur especially in females and the time sharing the same environment is the key factor in inducing the efficacy of emotional contagion.

Evolution of Pallial Areas and Networks Involved in Sociality: Comparison Between Mammals and Sauropsids

Birds are extremely interesting animals for studying the neurobiological basis of cognition and its evolution. They include species that are highly social and show high cognitive capabilities. Moreover, birds rely more on visual and auditory cues than on olfaction for social behavior and cognition, just like primates. In primates, there are two major brain networks associated to sociality: (1) one related to perception and decision-making, involving the pallial amygdala (with the basolateral complex as a major component), the temporal and temporoparietal neocortex, and the orbitofrontal cortex; (2) another one related to affiliation, including the medial extended amygdala, the ventromedial prefrontal and anterior cingulate cortices, the ventromedial striatum (largely nucleus accumbens), and the ventromedial hypothalamus. In this account, we used an evolutionary developmental neurobiology approach, in combination with published comparative connectivity and functional data, to identify areas and functional networks in the sauropsidian brain comparable to those of mammals that are related to decision-making and affiliation. Both in mammals and sauropsids, there is an important interaction between these networks by way of cross projections between areas of both systems.

Sexually dimorphic oxytocin receptor-expressing neurons in the preoptic area of the mouse brain

Oxytocin is involved in the regulation of social behaviors including parental behaviors in a variety of species. Oxytocin triggers social behaviors by binding to oxytocin receptors (OXTRs) in various parts of the brain. OXTRs are present in the preoptic area (POA) where hormone-sensitive sexually dimorphic nuclei exist. The present study was conducted to examine whether sex differences exist in the distribution of neurons expressing OXTRs in the POA. Using OXTR-Venus (an enhanced variant of yellow fluorescent protein) mice, the distribution of OXTR-Venus cells in the POA was compared between sexes. The total number of OXTR-Venus cells in the medial POA (MPOA) was significantly greater in females than in males. No detectable OXTR-Venus cells were observed in the anteroventral periventricular nucleus (AVPV) within the MPOA in most of the brain sections from males. We further examined the total number of OXTR-Venus cells in the AVPV and the rest of the MPOA between the sexes. The total number of OXTR-Venus cells in the AVPV in females (615 ± 43) was significantly greater than that in males (14 ± 2), whereas the total number of OXTR-Venus cells in the rest of the MPOA did not differ significantly between the sexes. Thus, the sexually dimorphic expression of OXTR-Venus specifically occurred in the AVPV, but not in the rest of the MPOA. We also examined whether the expression of OXTR in the AVPV is driven by the female gonadal hormone, estrogen. Immunocytochemistry and single-cell RT-PCR revealed the presence of the estrogen receptor α in OXTR-Venus cells in the female AVPV. Moreover, ovariectomy resulted in the absence of OXTR-Venus expression in the AVPV, whereas estrogen replacement therapy restored OXTR-Venus expression. These results demonstrate that the expression of OXTR in the AVPV is primarily female specific and estrogen dependent. The presence of the sexually dimorphic expression of OXTR in the AVPV suggests the involvement of OXTR neurons in the AVPV in the regulation of female-specific behavior and/or physiology.

Association of Polymorphism of Arginine-Vasopressin Receptor 1A (AVPR1a) Gene With Trust and Reciprocity

Oxytocin (OXT) is known to play an important role in trust, whereas the involvement of other peptide hormones has not been evaluated. In this study, we focused on microsatellite polymorphisms in the intron of the arginine-vasopressin receptor 1a (AVPR1a) gene and examined whether the association between the repeat lengths in the intron of AVPR1a is associated with trust and reciprocity in humans. Four-hundred and thirty-three participants played the trust game, answered the attitudinal trust question, and their buccal cells were collected. Results showed that men with a short form of AVPR1a tend to send more money to the opponent, even if there is a possibility of being betrayed by the opponent. Additionally, people with a short form of AVPR1a tended to return money to the opponent who trusts them. However, attitudinal trust was not associated with AVPR1a. These results indicate that arginine-vasopressin receptor 1a plays an important role in trust and reciprocal behaviors.

Endogenous oxytocin response to film scenes of attachment and loss is pronounced in schizophrenia

Background

Oxytocin (OXT) is critically involved in the regulation of attachment and interpersonal function. In this study, emotional children’s movies were used to stimulate OXT secretion in patients with schizophrenia and healthy controls (HCs). Furthermore, associations of OXT levels with measures of attachment style (Psychosis Attachment Measure), childhood adversity (Childhood Trauma Questionnaire) and symptom severity [Positive and Negative Syndrome Scale (PANSS)] were considered.

Methods

In 35 patients with schizophrenia and 35 matched HCs, radioimmunoassay with sample extraction was used to determine OXT plasma levels before and after viewing of movie scenes portraying emotional bonding and loss and compared to a non-emotional condition.

Results

Statistical analysis indicated lower baseline OXT levels in female patients than in all other groups. OXT reactivity during emotional movies was significantly higher in patients when compared to HCs. OXT reactivity during the control movie related to PANSS `general psychopathology’. No significant associations appeared between baseline or induced OXT levels and other PANSS subscales, attachment style or childhood adversity in patients.

Conclusions

Our findings suggest differences of baseline OXT and a higher OXT reactivity toward strong emotional stimuli in patients with schizophrenia, suggesting a role of OXT as a gender- and context-dependent modulator of socio-emotional function.

Pattern of fos activation in the ventral tegmental area (VTA) of male prairie vole's (Microtus ochrogaster) in response to infant-related stimuli

Prairie voles are socially monogamous mammals that form pair bonds and display paternal care. This study was focused on the male prairie vole's neuronal responses to infant-related odors. Using the fos protein as a measure of neuronal activation, we examined the brain responses of males to infant-related odors. Prior to testing, the subjects had cohabited for two weeks with either a male sibling (Male-Cohabited) or an unrelated female (Female-Cohabited). Given that paternal behavior of male prairie voles is enhanced after two-weeks of cohabitation with a mate, we hypothesized that fos activation in brain regions involved in caring must be increased in response to infants or their odors but not in response to water or sub-adult odors. To test this hypothesis, we analyzed the pattern of fos expression in the ventral tegmental area (VTA) and the bed nucleus of the stria terminals (BNST) two hours after Male-Cohabited and Female-Cohabited males were exposed to either two live infants or to odors of infants, sub-adults or water. Results showed differences in fos expression within the VTA between Male-Cohabited and Female-Cohabited subjects that were exposed to infants and infant odors. The type of cohabitation had no effect on fos expression within the BNST, but the pattern of fos activation in this region differed by the type of odor to which the subjects were exposed. Together, the data indicate that female sensory cues during post-mating cohabitation may be processed within the VTA to direct the male prairie vole's responses towards infants.

A Data Structure for Real-Time Aggregation Queries of Big Brain Networks

Recent advances in neuro-imaging allowed big brain-initiatives and consortia to create vast resources of brain data that can be mined by researchers for their individual projects. Exploring the relationship between genes, brain circuitry, and behavior is one of the key elements of neuroscience research. This requires fusion of spatial connectivity data at varying scales, such as whole brain correlated gene expression, structural and functional connectivity. With ever-increasing resolution, these tend to exceed the past state-of-the art in size and complexity by several orders of magnitude. Since current analytical workflows in neuroscience involve time-consuming manual data-aggregation, incorporating efficient techniques for handling big connectivity data is a necessity. We propose a novel data structure enabling the interactive exploration of heterogeneous neurobiological connectivity data with billions of edges. Based on this data structure we realized Aggregation Queries, i.e. the aggregated connectivity from, to or between brain areas allows experts to compare the multimodal networks residing at different scales, or levels of hierarchically organized anatomical atlases. Executed on-demand on volumetric gene expression and connectivity data, they allow an interactive dissection of networks in real-time and based on their spatial context. The data structure is optimized in order to be accessible directly from the hard disk, since connectivity of large-scale networks typically exceeds the memory size of current consumer level PCs. This allows experts to embed and explore their own experimental data in the framework of public data resources without the need for their own large-scale infrastructure. Our data structure outperforms state-of-the-art graph engines in retrieving connectivity of arbitrary user defined local brain areas. We demonstrate the feasibility of our approach by analyzing fear-related functional neuroanatomy in mice. Further, we show its versatility by comparing multimodal brain networks linked to autism. Importantly, we achieve cross-species congruence in retrieving human psychiatric traits networks, which facilitates the selection of neural substrates to be further studied in mouse models.

Nicotinamide as Independent Variable for Intelligence, Fertility, and Health: Origin of Human Creative Explosions?

Meat and nicotinamide acquisition was a defining force during the 2-million-year evolution of the big brains necessary for, anatomically modern, Homo sapiens to survive. Our next move was down the food chain during the Mesolithic 'broad spectrum', then horticultural, followed by the Neolithic agricultural revolutions and progressively lower average 'doses' of nicotinamide. We speculate that a fertility crisis and population bottleneck around 40 000 years ago, at the time of the Last Glacial Maximum, was overcome by Homo (but not the Neanderthals) by concerted dietary change plus profertility genes and intense sexual selection culminating in behaviourally modern Homo sapiens. Increased reliance on the 'de novo' synthesis of nicotinamide from tryptophan conditioned the immune system to welcome symbionts, such as TB (that excrete nicotinamide), and to increase tolerance of the foetus and thereby fertility. The trade-offs during the warmer Holocene were physical and mental stunting and more infectious diseases and population booms and busts. Higher nicotinamide exposure could be responsible for recent demographic and epidemiological transitions to lower fertility and higher longevity, but with more degenerative and auto-immune disease.

Evolution of affiliation: patterns of convergence from genomes to behaviour

Affiliative behaviours have evolved many times across animals. Research on the mechanisms underlying affiliative behaviour demonstrates remarkable convergence across species spanning wide evolutionary distances. Shared mechanisms have been identified with genomic approaches analysing genetic variants and gene expression differences as well as neuroendocrine and molecular approaches exploring the role of hormones and signalling molecules. We review the genomic and neural basis of pair bonding and parental care across diverse taxa to shed light on mechanistic patterns that underpin the convergent evolution of affiliative behaviour. We emphasize that mechanisms underlying convergence in complex phenotypes like affiliation should be evaluated on a continuum, where signatures of convergence may vary across levels of biological organization. In particular, additional comparative studies within and across major vertebrate lineages will be essential in resolving when and why shared neural substrates are repeatedly targeted in the independent evolution of affiliation, and how similar mechanisms are evolutionarily tuned to give rise to species-specific variations in behaviour. This article is part of the theme issue 'Convergent evolution in the genomics era: new insights and directions'.

Role of basal ganglia neurocircuitry in the pathology of psychiatric disorders

Over the last few decades, advances in human and animal-based techniques have greatly enhanced our understanding of the neural mechanisms underlying psychiatric disorders. Many of these studies have indicated connectivity between and alterations within basal ganglia structures to be particularly pertinent to the development of symptoms associated with several of these disorders. Here we summarize the connectivity, molecular composition, and function of sites within basal ganglia neurocircuits. Then we review the current literature from both human and animal studies concerning altered basal ganglia function in five common psychiatric disorders: obsessive-compulsive disorder, substance-related and addiction disorders, major depressive disorder, generalized anxiety disorder, and schizophrenia. Finally, we present a model based upon the findings of these studies that highlights the striatum as a particularly attractive target for restoring normal function to basal ganglia neurocircuits altered within psychiatric disorder patients.

The neural and genetic correlates of satisfying sexual activity in heterosexual pair-bonds

INTRODUCTION

In humans, satisfying sexual activity within a pair-bond plays a significant role in relationship quality and maintenance, beyond reproduction. However, the neural and genetic correlates for this basic species-supporting function, in response to a pair-bonded partner, are unknown.

METHODS

We examined the neural correlates of oxytocin- (Oxtr rs53576) and vasopressin- (Avpr1a rs3) receptor genotypes with sexual satisfaction and frequency, among a group of individuals in pair-bonds (M relationship length = 4.1 years). Participants were scanned twice (with functional MRI), about 1-year apart, while viewing face images of their spouse and a familiar, neutral acquaintance.

RESULTS

Sex satisfaction scores showed significant interactions with Oxtr and Avpr variants associated with social behaviors in a broad network of regions involved in reward and motivation (ventral tegmental area, substantia nigra [SN], and caudate), social bonding (ventral pallidum), emotion and memory (amygdala/hippocampus), hormone control (hypothalamus); and somatosensory and self-other processing (SII, frontal, and temporal lobe). Sexual frequency interactions also showed activations in the SN and paraventricular hypothalamus for Avpr, and the prefrontal cortex for Oxtr.

CONCLUSIONS

Satisfying sexual activity in pair-bonds is associated with activation of subcortical structures that support basic motivational and physiological processes; as well as cortical regions that mediate complex thinking, empathy, and self-other processes highlighting the multifaceted role of sex in pair-bonds. Oxtr and Avpr gene variants may further amplify both basic and complex neural processes for pair-bond conservation and well-being.

Isotocin increases female avoidance of males in a coercive mating system: Assessing the social salience hypothesis of oxytocin in a fish species

The nonapeptide oxytocin (and its fish homolog isotocin (IT)) is an evolutionarily-conserved hormone associated with social behaviors across most vertebrate taxa. Oxytocin has traditionally been regarded as a prosocial hormone, but studies on social cognition in mammalian models suggest it may play a more nuanced role in modulating social discrimination based on social salience and stimulus valence. Here we test IT and its role in regulating female social decision-making and anxiety behaviors in a live-bearing fish with a male coercive mating system. Gambusia affinis males engage in a forced mating strategy, with frequent harassment and attempted copulatory thrusts directed towards unwilling females. Exogenous IT produced anxiolytic responses in female G. affinis that altered exploration (time in center of tank) but not time in dark vs. light regions of the tank. Exogenous IT also produced context-specific changes in social tendency: IT-treated G. affinis females spent less time associating with males while association time with conspecific females was not altered. Further, while overall activity levels were not changed by IT treatment, the amount of social behaviors IT-treated females directed towards males, but not females, was reduced. Our results support the social salience hypothesis of oxytocin action in a teleost and suggest that oxytocin's critical input into social cognitive processing is conserved across vertebrate taxa.

The negative effects of social bond disruption are partially ameliorated by sertraline administration in prairie voles

Negative social experiences influence both depression and cardiovascular dysfunction. Many individuals who experience negative mood states or cardiovascular conditions have limited social support. Therefore, investigation of drug treatments that may protect against the consequences of social stress will aid in designing effective treatment strategies. The current study used an animal model to evaluate the protective effect of sertraline administration on behavioral and cardiovascular consequences of social stress. Specifically, male prairie voles (Microtus ochrogaster), which are socially monogamous rodents that share several behavioral and physiological characteristics with humans, were isolated from a socially-bonded female partner, and treated with sertraline (16 mg/kg/day, ip) or vehicle during isolation. Unexpectedly, sertraline did not protect against depression-relevant behaviors, and it was associated with increased short- and long-term heart rate responses. However, sertraline administration improved heart rate variability recovery following a behavioral stressor, including increased parasympathetic regulation, and altered long-term neuronal activity in brain regions that modulate autonomic control and stress reactivity. These results indicate that sertraline may partially protect against the consequences of social stressors, and suggest a mechanism through which sertraline may beneficially influence neurobiological control of cardiac function.

Sexual dimorphism of oxytocin and vasopressin in social cognition and behavior

The neuropeptides oxytocin (OT) and vasopressin (VP) are hormones that are known to mediate social behavior and cognition, but their influence may be sex-dependent. This paper aims to provide a comprehensive review of the sex-related influence of OT and VP on social cognition, focusing on partner preference and sexual orientation, trust and relevant behaviors, memory modulation, and emotion regulation. Most studies have suggested that OT facilitates familiar-partner preference in both sexes, with females being more significant, increased trust in others, especially for male, enhanced memory in either sex, and reduced anxious emotion in males. However, VP-regulated social cognition has been less studied. Other relevant studies have indicated that VP facilitated familiar-partner preference, improved memory, induced empathy formation, increased positive-emotion recognition, and induced anxiety without any sex difference. However, there was a male preponderance among studies, and results were often too complex to draw firm conclusions. Clarifying the interplay between OT/VP and sex hormones in the regulation of social cognition is necessary for further applications.

Dopamine receptor manipulation does not alter patterns of partner preference in long-term marmoset pairs

The relationship between socially monogamous mates is dynamic and regulated by neurobiological influences. Research in rodent models has indicated a key role for the neurotransmitter dopamine (DA) and its receptors (DAR) in mediating the formation and maintenance of monogamous bonds. DAR activation was pharmacologically manipulated in marmosets housed in long-term pairs. Marmosets exposed to DAR manipulation were tested in a partner preference test under two social conditions: one in which their mate could visually observe their interactions with an opposite-sex individual, and one in which their pair mate could not visually observe these interactions. Marmosets displayed a spatial preference for the mate compared to an unfamiliar conspecific, however, they displayed a sexual preference for an unfamiliar conspecific over their mate. D1R manipulation had no impact on marmoset partner preference. However, activation of D2Rs reduced the time marmosets spent in contact with either stimulus animal, indicating a decrease in social interest, but did not reduce time spent in proximity to the stimulus animals nor number of sexual solicitations. Additionally, social context (visibility of the mate) did not influence marmoset behavior. These findings suggest that D2Rs may be involved in regulating generalized, but not partner-specific, social interest in marmoset monkeys.

Epigenetic Regulation of the Social Brain

Social behavior, a highly adaptive and crucial component of mammalian life, is regulated by particularly sensitive regulatory brain mechanisms. Substantial evidence implicates classical epigenetic mechanisms including histone modifications, DNA methylation, and nucleosome remodeling as well as nonclassical mechanisms mediated by noncoding RNA in the regulation of social behavior. These mechanisms collectively form the 'epigenetic network' that orchestrates genomic integration of salient and transient social experiences. Consequently, its dysregulation has been linked to behavioral deficits and psychopathologies. This review focuses on the role of the epigenetic network in regulating the enduring effects of social experiences during early-life, adolescence, and adulthood. We discuss research in animal models, primarily rodents, and associations between dysregulation of epigenetic mechanisms and human psychopathologies, specifically autism spectrum disorder (ASD) and schizophrenia.

Complementary Neural Circuits for Divergent Effects of Oxytocin: Social Approach Versus Social Anxiety

Oxytocin (OT) is widely known for promoting social interactions, but there is growing appreciation that it can sometimes induce avoidance of social contexts. The social salience hypothesis posed an innovative solution to these apparently opposing actions by proposing that OT enhances the salience of both positive and negative social interactions. The mesolimbic dopamine system was put forth as a likely system to evaluate social salience owing to its well-described role in motivation. Evidence from several sources supports the premise that OT acting within the nucleus accumbens and ventral tegmental area facilitates social reward and approach behavior. However, in aversive social contexts, additional pathways play critical roles in mediating the effects of OT. Recent data indicate that OT acts in the bed nucleus of the stria terminalis to induce avoidance of potentially dangerous social contexts. Here, we review evidence for neural circuits mediating the effects of OT in appetitive and aversive social contexts. Specifically, we propose that distinct but potentially overlapping circuits mediate OT-dependent social approach or social avoidance. We conclude that a broader and more inclusive consideration of neural circuits of social approach and avoidance is needed as the field continues to evaluate the potential of OT-based therapeutics.

Committed for the long haul: Do nonapeptides regulate long-term pair maintenance in zebra finches?

The nonapeptides (oxytocin, vasopressin, and their non-mammalian homologs) regulate a number of social behaviors across vertebrates including monogamous pair bonds in mammals. Recent work on zebra finches has shown an important role for these neurohormones in establishing avian pair bonds as well. However, studies on the role of nonapeptides in maintaining pair bonds after pair formation are lacking. The goal of the present study was to investigate the effects of an oxytocin receptor antagonist (OTA) on pair maintenance behaviors in the monogamous zebra finch. I injected established zebra finch pairs over three days with either 5 μg of an OTA or a vehicle control, and separated the partners for one hour, after which partners were reunited and their reunion recorded on video for 30 min. Videos were then coded to measure singing, affiliative (allopreening, clumping, following), and aggressive (pecking) behaviors. These behaviors were also measured both on the day before injections to establish a pre-treatment level and two days after the last injection. Control and antagonist treated birds did not differ in the amount of time spent clumping or the frequency of pecking across the experiment. However, both male and female zebra finches that received OTA significantly reduced the amount of time spent following their partner. Females given the OTA treatment reduced allopreening and males given the OTA treatment reduced the frequency of singing bouts directed at their partners relative to controls. These results suggest that the nonapeptides play a role in regulating some, but not all, pair maintenance behaviors in experienced zebra finches.

Increased anxiety and decreased sociability induced by paternal deprivation involve the PVN-PrL OTergic pathway

Early adverse experiences often have devastating consequences. However, whether preweaning paternal deprivation (PD) affects emotional and social behaviors and their underlying neural mechanisms remain unexplored. Using monogamous mandarin voles, we found that PD increased anxiety-like behavior and attenuated social preference in adulthood. PD also decreased the number of oxytocin (OT)-positive neurons projecting from the paraventricular nucleus (PVN) and reduced the levels of the medial prefrontal cortex OT receptor protein in females and of the OT receptor and V1a receptor proteins in males. Intra-prelimbic cortical OT injections reversed the PD-induced changes in anxiety-like behavior and social preferences. Optogenetic activation of the prelimbic cortex OT terminals from PVN OT neurons reversed the PD-induced changes in emotion and social preference behaviors, whereas optogenetic inhibition was anxiogenic and impaired social preference in naive voles. These findings demonstrate that PD increases anxiety-like behavior and attenuates social preferences through the involvement of PVN OT neuron projections to the prelimbic cortex.

Parental care early in life is essential for normal development of the brain in humans and some other animals. It also lays the ground work for healthy behaviors later in life. Many studies have looked at the importance of a mother’s care, but less attention has been paid to the role played by fathers. Research shows that children who grow up without a father are at risk of emotional and behavioral problems later in life. But it is not clear how missing a father’s care affects brain development.

Oxytocin, a chemical produced by a part of the brain called the paraventricular nucleus, plays a key role in parental bonding. Another part of the brain called the prelimbic cortex regulates many emotions and many complex behaviors. Studying animals, like the mandarin vole, that form strong bonds with both parents is one way to learn more about how the loss of paternal care affects oxytocin or emotional and behavioral health.

Now, He et al. show that mandarin voles raised without a father are more anxious and socialize less with other voles than those raised with a father. The voles deprived of paternal care also have fewer oxytocin-producing cells in the paraventricular nucleus and fewer receptors for oxytocin in the prelimbic cortex. Injecting oxytocin into the prelimbic cortex eliminated the anxious and antisocial behavior seen in the voles lacking paternal care. Using a technique called optogenetics to restore the release of oxytocin in the prelimbic cortex reduced anxious behavior and restored normal social interactions. Using the same approach to interfere with communication between the paraventricular nucleus and prelimbic cortex in voles raised with a father also triggered anxious and antisocial behavior.

The experiments reveal that fathers play an important role in brain and behavioral development in mandarin voles. He et al. show that a lack of paternal care leads to deficits in oxytocin and a poor communication between the paraventricular nucleus and prelimbic cortex that contribute to emotional and social abnormalities in the voles. More studies are needed to determine father’s care has similar effects in humans. But if this relationship is confirmed, it might lead scientists to develop new strategies for treating psychiatric disorders in people deprived of paternal care.

Oxytocin receptor knockout prairie voles generated by CRISPR/Cas9 editing show reduced preference for social novelty and exaggerated repetitive behaviors

Behavioral neuroendocrinology has benefited tremendously from the use of a wide range of model organisms that are ideally suited for particular questions. However, in recent years the ability to manipulate the genomes of laboratory strains of mice has led to rapid advances in our understanding of the role of specific genes, circuits and neural populations in regulating behavior. While genome manipulation in mice has been a boon for behavioral neuroscience, the intensive focus on the mouse restricts the diversity in behavioral questions that can be investigated using state-of-the-art techniques. The CRISPR/Cas9 system has great potential for efficiently generating mutants in non-traditional animal models and consequently to reinvigorate comparative behavioral neuroendocrinology. Here we describe the efficient generation of oxytocin receptor (Oxtr) mutant prairie voles (Microtus ochrogaster) using the CRISPR/Cas9 system, and describe initial behavioral phenotyping focusing on behaviors relevant to autism. Oxtr mutant male voles show no disruption in pup ultrasonic vocalization, anxiety as measured by the open field test, alloparental behavior, or sociability in the three chamber test. Mutants did however show a modest elevation in repetitive behavior in the marble burying test, and an impairment in preference for social novelty. The ability to efficiently generate targeted mutations in the prairie vole genome will greatly expand the utility of this model organism for discovering the genetic and circuit mechanisms underlying complex social behaviors, and serves as a proof of principle for expanding this approach to other non-traditional model organisms.

Cumulative Risk of the Oxytocin Receptor Gene Interacts with Prenatal Exposure to Oxytocin Receptor Antagonist to Predict Children's Social Communication Development

Compelling evidence for the far-reaching role of oxytocin (OT) in social cognition and affiliative behaviors set the basis for examining the association between genetic variation in the OT receptor (OXTR) gene and risk for autism spectrum disorder (ASD). In the current study, gene-environment interaction between OXTR and prenatal exposure to either OT or OXTR antagonist (OXTRA) in predicting early social communication development was examined. One hundred and fifty-three children (age: M = 4.32, SD = 1.07) were assigned to four groups based on prenatal history: children whose mothers prenatally received OXTRA and Nifedipine to delay preterm labor (n = 27); children whose mothers received Nifedipine only to delay preterm labor (n = 35); children whose mothers received OT for labor augmentation (n = 56), and a no intervention group (n = 35). Participants completed a developmental assessment of intelligence quotient (IQ), adaptive behavior, and social communication abilities. DNA was extracted via buccal swab. A genetic risk score was calculated based on four OXTR single nucleotide polymorphisms (rs53576, rs237887, rs1042778, and rs2254298) previously reported to be associated with ASD symptomatology. OXTRrisk-allele dosage was associated with more severe autism diagnostics observation schedule (ADOS) scores only in the OXTRA group. In contrast, in the Nifedipine, OT, and no intervention groups, OXTRrisk-allele dosage was not associated with children's ADOS scores. These findings highlight the importance of both genetic and environmental pathways of OT in signaling early social development and raise the need for further research in this field. Autism Res 2019, 12: 1087-1100. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: In the current study, we examined if the association between prenatal exposure to an oxytocin receptor antagonist (OXTRA) and autism spectrum disorder (ASD) related impairments are dependent on an individual's genetic background for the oxytocin receptor gene (OXTR). Children who carried a greater number of risk alleles for the OXTR gene and whose mothers received OXTRA to delay preterm labor showed more ASD-related impairments. The results highlight the importance of both genetic and environmental pathways of oxytocin in shaping early social development.

Sex-Related Differences in Plasma Oxytocin Levels in Humans

Background:

Increasing evidence supports a key role of Oxytocin (OT) as a modulator of social relationships in mammals.

Objective:

The aim of the present study was to investigate possible sex-related differences in plasma OT levels in human beings.

Methods:

Forty-five healthy men and 45 women (mean age: 34.9 ± 6.2 years), were included in the study. Plasma preparation, peptide extraction and OT radioimmunoassay were carried out according to standardized methods.

Results:

The results showed that OT plasma levels (pg / ml, mean ± SD) were significantly higher in women than in men (4.53 ± 1.18 vs 1.53 ± 1.19, p ˂ 0.001).

Conclusions:

The present finding demonstrates sex-related differences in plasma OT levels in humans. It is tempting to hypothesize that such differences might be related to behaviours, attitudes, as well as susceptibility to stress response, resilience and social emotions specific of women and men.

Neural mechanisms of social homeostasis

Social connections are vital to survival throughout the animal kingdom and are dynamic across the life span. There are debilitating consequences of social isolation and loneliness, and social support is increasingly a primary consideration in health care, disease prevention, and recovery. Considering social connection as an "innate need," it is hypothesized that evolutionarily conserved neural systems underlie the maintenance of social connections: alerting the individual to their absence and coordinating effector mechanisms to restore social contact. This is reminiscent of a homeostatic system designed to maintain social connection. Here, we explore the identity of neural systems regulating "social homeostasis." We review findings from rodent studies evaluating the rapid response to social deficit (in the form of acute social isolation) and propose that parallel, overlapping circuits are engaged to adapt to the vulnerabilities of isolation and restore social connection. By considering the neural systems regulating other homeostatic needs, such as energy and fluid balance, we discuss the potential attributes of social homeostatic circuitry. We reason that uncovering the identity of these circuits/mechanisms will facilitate our understanding of how loneliness perpetuates long-term disease states, which we speculate may result from sustained recruitment of social homeostatic circuits.

D2 dopamine receptor activation induces female preference for male song in the monogamous zebra finch

The evolutionary conservation of neural mechanisms for forming and maintaining pair bonds is unclear. Oxytocin, vasopressin and dopamine (DA) transmitter systems have been shown to be important in pair-bond formation and maintenance in several vertebrate species. We examined the role of dopamine in formation of song preference in zebra finches, a monogamous bird. Male courtship song is an honest signal of sexual fitness; thus, we measured female song preference to evaluate the role of DA in mate selection and pair-bond formation, using an operant conditioning paradigm. We found that DA acting through the D2 receptor, but not the D1 receptor, can induce a song preference in unpaired female finches and that blocking the D2 receptor abolished song preference in paired females. These results suggest that similar neural mechanisms for pair-bond formation are evolutionarily conserved in rodents and birds.

Insular function in autism: Update and future directions in neuroimaging and interventions

The insular cortex, hidden within the lateral sulcus of the human brain, participates in a range of cognitive, affective, and sensory functions. Autism spectrum disorder (ASD), a neurodevelopmental condition affecting all of these functional domains, has increasingly been linked with atypical activation and connectivity of the insular cortices. Here we review the latest research linking atypical insular function to a range of behaviors characteristic of ASD, with an emphasis on neuroimaging findings in the domains of social cognition and executive function. We summarize some of the recent work linking the insula to interventions in autism, including oxytocin-based pharmacological treatments and music therapy. We suggest that future directions likely to yield significant insights into insular pathology in ASD include the analysis of the dynamics of this brain region. We also conclude that more basic research is necessary on the use of oxytocin pharmacotherapy, and larger studies addressing participant heterogeneity are needed on the use of music therapy in ASD. Long-term studies are needed to ascertain sustained effects of these interventions.

Evolutionary diversity as a catalyst for biological discovery

The tremendous diversity of animal behaviors has inspired generations of scientists from an array of biological disciplines. To complement investigations of ecological and evolutionary factors contributing to behavioral evolution, modern sequencing, gene editing, computational and neuroscience tools now provide a means to discover the proximate mechanisms upon which natural selection acts to generate behavioral diversity. Social behaviors are motivated behaviors that can differ tremendously between closely related species, suggesting phylogenetic plasticity in their underlying biological mechanisms. In addition, convergent evolution has repeatedly given rise to similar forms of social behavior and mating systems in distantly related species. Social behavioral divergence and convergence provides an entry point for understanding the neurogenetic mechanisms contributing to behavioral diversity. We argue that the greatest strides in discovering mechanisms contributing to social behavioral diversity will be achieved through integration of interdisciplinary comparative approaches with modern tools in diverse species systems. We review recent advances and future potential for discovering mechanisms underlying social behavioral variation; highlighting patterns of social behavioral evolution, oxytocin and vasopressin neuropeptide systems, genetic/transcriptional "toolkits," modern experimental tools, and alternative species systems, with particular emphasis on Microtine rodents and Lake Malawi cichlid fishes.

A computational perspective on social attachment

Humans depend on social relationships for survival and wellbeing throughout life. Yet, individuals differ markedly in their ability to form and maintain healthy social relationships. Here we use a simple mathematical model to formalize the contention that a person's attachment style is determined by what they learn from relationships early in life. For the sake of argument, we therefore discount individual differences in the innate personality or attachment style of a child, assuming instead that all children are simply born with an equivalent, generic, hardwired desire and instinct for social proximity, and a capacity to learn. In line with the evidence, this innate endowment incorporates both simple bonding instincts and a capacity for cognitively sophisticated beliefs and generalizations. Under this assumption, we then explore how distinct attachment styles might emerge through interaction with the child's early caregivers. Our central question is, how an apparently adaptive capacity to learn can yield enduring maladaptive attachment styles that generalize to new relationships. We believe extensions of our model will ultimately help clarify the complex interacting mechanisms - both acquired and innate - that underpin individual differences in attachment styles. While our model is relatively abstract, we also attempt some connection to known biological mechanisms of attachment.