Social conditioned place preference in the captive ground squirrel (Ictidomys tridecemlineatus): Social reward as a natural phenotype

Structural alterations in the amygdala and impaired social incentive learning in a mouse model of a genetic variant associated with neurodevelopmental disorders

Copy number variants (CNVs) are robustly associated with psychiatric disorders and their dimensions and changes in brain structures and behavior. However, as CNVs contain many genes, the precise gene-phenotype relationship remains unclear. Although various volumetric alterations in the brains of 22q11.2 CNV carriers have been identified in humans and mouse models, it is unknown how the genes in the 22q11.2 region individually contribute to structural alterations and associated mental illnesses and their dimensions. Our previous studies have identified Tbx1, a T-box family transcription factor encoded in 22q11.2 CNV, as a driver gene for social interaction and communication, spatial and working memory, and cognitive flexibility. However, it remains unclear how TBX1 impacts the volumes of various brain regions and their functionally linked behavioral dimensions. In this study, we used volumetric magnetic resonance imaging analysis to comprehensively evaluate brain region volumes in congenic Tbx1 heterozygous mice. Our data show that the volumes of anterior and posterior portions of the amygdaloid complex and its surrounding cortical regions were reduced in Tbx1 heterozygous mice. Moreover, we examined the behavioral consequences of an altered volume of the amygdala. Tbx1 heterozygous mice were impaired for their ability to detect the incentive value of a social partner in a task that depends on the amygdala. Our findings identify the structural basis for a specific social dimension associated with loss-of-function variants of TBX1 and 22q11.2 CNV.

Structural alterations in the amygdala and impaired social incentive learning in a mouse model of a genetic variant associated with neurodevelopmental disorders

Copy number variants (CNVs) are robustly associated with psychiatric disorders and their dimensions and changes in brain structures and behavior. However, as CNVs contain many genes, the precise gene-phenotype relationship remains unclear. Although various volumetric alterations in the brains of 22q11.2 CNV carriers have been identified in humans and mouse models, it is unknown how the genes in the 22q11.2 region individually contribute to structural alterations and associated mental illnesses and their dimensions. Our previous studies have identified Tbx1 , a T-box family transcription factor encoded in 22q11.2 CNV, as a driver gene for social interaction and communication, spatial and working memory, and cognitive flexibility. However, it remains unclear how TBX1 impacts the volumes of various brain regions and their functionally linked behavioral dimensions. In this study, we used volumetric magnetic resonance imaging analysis to comprehensively evaluate brain region volumes in congenic Tbx1 heterozygous mice. Our data show that the volumes of anterior and posterior portions of the amygdaloid complex and its surrounding cortical regions were reduced in Tbx1 heterozygous mice. Moreover, we examined the behavioral consequences of an altered volume of the amygdala. Tbx1 heterozygous mice were impaired for their ability to detect the incentive value of a social partner in a task that depends on the amygdala. Our findings identify the structural basis for a specific social dimension associated with loss-of-function variants of TBX1 and 22q11.2 CNV.

Paternal Cocaine in Mice Alters Social Behavior and Brain Oxytocin Receptor Density in First Generation Offspring

It is well established that the damaging effects of drugs of abuse, such as cocaine, can extend beyond the user to their offspring. While most preclinical models of the generational effects of cocaine abuse have focused on maternal effects, we, and others, report distinct effects on offspring sired by fathers treated with cocaine prior to breeding. However, little is known about the effects of paternal cocaine use on first generation (F1) offspring's social behaviors. Here, we expand upon our model of oral self-administered paternal cocaine use to address the idea that paternal cocaine alters first generation offspring social behaviors through modulation of the oxytocin system. F1 cocaine-sired males displayed unaltered social recognition vs. non-cocaine sired controls but showed increased investigation times that were not related to altered olfaction. Paternal cocaine did not alter F1 male-aggression behavior or depression-like behaviors, but cocaine-sired males did display decreased anxiety-like behaviors. Female F1 behavior was similarly examined, but there were no effects of paternal cocaine. Cocaine-sired male mice also exhibited localized oxytocin receptor expression differences vs. controls in several brain regions regulating social behavior. These results provide evidence for effects of paternal cocaine exposure on social behaviors in male offspring with associated alterations in central oxytocin transmission.

A meta-analysis of sex differences in animal personality: no evidence for the greater male variability hypothesis

The notion that men are more variable than women has become embedded into scientific thinking. For mental traits like personality, greater male variability has been partly attributed to biology, underpinned by claims that there is generally greater variation among males than females in non-human animals due to stronger sexual selection on males. However, evidence for greater male variability is limited to morphological traits, and there is little information regarding sex differences in personality-like behaviours for non-human animals. Here, we meta-analysed sex differences in means and variances for over 2100 effects (204 studies) from 220 species (covering five broad taxonomic groups) across five personality traits: boldness, aggression, activity, sociality and exploration. We also tested if sexual size dimorphism, a proxy for sex-specific sexual selection, explains variation in the magnitude of sex differences in personality. We found no significant differences in personality between the sexes. In addition, sexual size dimorphism did not explain variation in the magnitude of the observed sex differences in the mean or variance in personality for any taxonomic group. In sum, we find no evidence for widespread sex differences in variability in non-human animal personality.

Large-scale functional brain networks for consciousness

The generation and maintenance of consciousness are fundamental but difficult subjects in the fields of psychology, philosophy, neuroscience, and medicine. However, recent developments in neuro-imaging techniques coupled with network analysis have greatly advanced our understanding of consciousness. The present review focuses on large-scale functional brain networks based on neuro-imaging data to explain the awareness (contents) and wakefulness of consciousness. Despite limitations, neuroimaging data suggests brain maps for important psychological and cognitive processes such as attention, language, self-referential, emotion, motivation, social behavior, and wakefulness. We considered a review of these advancements would provide new insights into research on the neural correlates of consciousness.

Correlates of maternal glucocorticoid levels in a socially flexible rodent

While it is generally accepted that social isolation has detrimental effects on social species, little is known about the importance of social interactions in less social species-particularly for wild reproductive females. We studied socially-flexible yellow-bellied marmots (Marmota flaviventer) and asked whether features of the social environment are associated with maternal fecal glucocorticoid metabolite (FGM) concentrations. Since changes in maternal baseline glucocorticoids may have positive or negative consequences for offspring fitness, we were also interested in estimating their relationship with measures of reproductive success. We fitted generalized linear mixed effects models to a dataset including maternal FGM measurements, social network metrics, maternal/alloparental care, and pup FGM and survival. Agonistic interactions were positively associated with maternal FGM levels, while mothers that engaged in relatively more affiliative interactions had reduced FGM levels when living in environments with low predator pressure. Pups associated with mothers exhibiting high FGM levels had low annual survival rates, received less maternal/alloparental care and had higher FGM levels. Interestingly, offspring from mothers with high FGM levels were more likely to survive the summer when born in small litters. In sum, social interactions likely influence and are influenced by glucocorticoid levels of facultatively social females. Potential benefits of social bonds may be context-specific, and agonistic interactions may be tightly correlated with fitness. Female marmots exhibiting high FGM levels had overall low reproductive success, which is predicted by the cort-fitness hypothesis. However, under adverse conditions, offspring summer survival can be maximized if pups are born in small litters.

Comparative role of reward in long-term peer and mate relationships in voles

This is a contribution to SI: SBN/ICN meeting. In social species, relationships may form between mates, parents and their offspring, and/or social peers. Prairie voles and meadow voles both form selective relationships for familiar same-sex peers, but differ in mating system, allowing comparison of the properties of peer and mate relationships. Prairie vole mate bonds are dopamine-dependent, unlike meadow vole peer relationships, indicating potential differences in the mechanisms and motivation supporting these relationships within and/or across species. We review the role of dopamine signaling in affiliative behavior, and assess the role of behavioral reward across relationship types. We compared the reinforcing properties of mate versus peer relationships within a species (prairie voles), and peer relationships across species (meadow and prairie voles). Social reinforcement was assessed using the socially conditioned place preference test. Animals were conditioned using randomly assigned, equally preferred beddings associated with social (CS+) and solitary (CS-) housing. Prairie vole mates, but not prairie or meadow vole peers, conditioned toward the social cue. A second study in peers used counter-conditioning to enhance the capacity to detect low-level conditioning. Time spent on CS+ bedding significantly decreased in meadow voles, and showed a non-significant increase in prairie voles. These data support the conclusion that mate relationships are rewarding for prairie voles. Despite selectivity of preferences for familiar individuals in partner preference tests, peer relationships in both species appear only weakly reinforcing or non-reinforcing. This suggests important differences in the pathways underlying these relationship types, even within species.

SHANK3 Downregulation in the Ventral Tegmental Area Accelerates the Extinction of Contextual Associations Induced by Juvenile Non-familiar Conspecific Interaction

Haploinsufficiency of the SHANK3 gene, encoding for a scaffolding protein located in the postsynaptic density of glutamatergic synapse, has been linked to forms of autism spectrum disorders (ASDs). It has been shown that SHANK3 controls the maturation of social reward circuits in the ventral tegmental area (VTA). Whether the impairments in associative learning observed in ASD relate to SHANK3 insufficiency restricted to the reward system is still an open question. Here, we first characterize a social-conditioned place preference (CPP) paradigm based on the direct and free interaction with a juvenile and non-familiar conspecific. In both group- and single-housed C57Bl6/j late adolescence male mice, this CPP protocol promotes the formation of social-induced contextual associations that undergo extinction. Interestingly, the downregulation of Shank3 expression in the VTA altered the habituation to a non-familiar conspecific during conditioning and accelerated the extinction of social-induced conditioned responses. Thus, inspired by the literature on drugs of abuse-induced contextual learning, we propose that acquisition and extinction of CPP might be used as behavioral assays to assess social-induced contextual association and “social-seeking” dysfunctions in animal models of psychiatric disorders.

Social Reward and Empathy as Proximal Contributions to Altruism: The Camaraderie Effect

Natural selection favors individuals to act in their own interests, implying that wild animals experience a competitive psychology. Animals in the wild also express helping behaviors, presumably at their own expense and suggestive of a more compassionate psychology. This apparent paradox can be partially explained by ultimate mechanisms that include kin selection, reciprocity, and multilevel selection, yet some theorists argue such ultimate explanations may not be sufficient and that an additional "stake in others" is necessary for altruism's evolution. We suggest this stake is the "camaraderie effect," a by-product of two highly adaptive psychological experiences: social motivation and empathy. Rodents can derive pleasure from access to others and this appetite for social rewards motivates individuals to live together, a valuable psychology when group living is adaptive. Rodents can also experience empathy, the generation of an affective state more appropriate to the situation of another compared to one's own. Empathy is not a compassionate feeling but it has useful predictive value. For instance, empathy allows an individual to feel an unperceived danger from social cues. Empathy of another's stance toward one's self would predict either social acceptance or ostracism and amplify one's physiological sensitivity to social isolation, including impaired immune responses and delayed wound healing. By contrast, altruistic behaviors would promote well-being in others and feelings of camaraderie from others, thereby improving one's own physiological well-being. Together, these affective states engender a stake in others necessary for the expression of altruistic behavior.

A Social Reinforcement Learning Hypothesis of Mutual Reward Preferences in Rats

Although the use of neuroimaging techniques has revealed much about the neural correlates of social decision making (SDM) in humans, it remains poorly understood how social stimuli are represented, and how social decisions are implemented at the neural level in humans and in other species. To address this issue, the establishment of novel animal paradigms allowing a broad spectrum of neurobiological causal manipulations and neurophysiological recordings provides an exciting tool to investigate the neural implementation of social valuation in the brain. Here, we discuss the potential of a rodent model, Rattus norvegicus, for the understanding of SDM and its neural underpinnings. Particularly, we consider recent data collected in a rodent prosocial choice task within a social reinforcement framework and discuss factors that could drive SDM in rodents.

The neurobiology of social play and its rewarding value in rats

In the young of many mammalian species, including humans, a vigorous and highly rewarding social activity is abundantly expressed, known as social play behaviour. Social play is thought to be important for the development of social, cognitive and emotional processes and their neural underpinnings, and it is disrupted in pediatric psychiatric disorders. Here, we summarize recent progress in our understanding of the brain mechanisms of social play behaviour, with a focus on its rewarding properties. Opioid, endocannabinoid, dopamine and noradrenaline systems play a prominent role in the modulation of social play. Of these, dopamine is particularly important for the motivational properties of social play. The nucleus accumbens has been identified as a key site for opioid and dopamine modulation of social play. Endocannabinoid influences on social play rely on the basolateral amygdala, whereas noradrenaline modulates social play through the basolateral amygdala, habenula and prefrontal cortex. In sum, social play behaviour is the result of coordinated activity in a network of corticolimbic structures, and its monoamine, opioid and endocannabinoid innervation.