In search of the neurobiological substrates for social playfulness in mammalian brains

The Incentive-Sensitization Theory of Addiction 30 Years On

The incentive-sensitization theory (IST) of addiction was first published in 1993, proposing that (a) brain mesolimbic dopamine systems mediate incentive motivation ("wanting") for addictive drugs and other rewards, but not their hedonic impact (liking) when consumed; and (b) some individuals are vulnerable to drug-induced long-lasting sensitization of mesolimbic systems, which selectively amplifies their "wanting" for drugs without increasing their liking of the same drugs. Here we describe the origins of IST and evaluate its status 30 years on. We compare IST to other theories of addiction, including opponent-process theories, habit theories of addiction, and prefrontal cortical dysfunction theories of impaired impulse control. We also address critiques of IST that have been raised over the years, such as whether craving is important in addiction and whether addiction can ever be characterized as compulsive. Finally, we discuss several contemporary phenomena, including the potential role of incentive sensitization in behavioral addictions, the emergence of addiction-like dopamine dysregulation syndrome in medicated Parkinson's patients, the role of attentional capture and approach tendencies, and the role of uncertainty in incentive motivation.

To Play or Not to Play? Effects of Playmate Familiarity and Social Isolation on Social Play Engagement in Three Laboratory Rat Strains

Social play is a motivating and rewarding behavior displayed by juveniles of many mammalian species, including humans and rats. Social play is vital to the development of social skills. Autistic children show less social play engagement which may contribute to their impairments in social skills. There is limited knowledge about what external conditions may positively or negatively influence social play engagement in humans or other animals. Therefore, we determined how two common external conditions, playmate familiarity and social isolation, modulate social play levels and social play defense tactics in juveniles of three common laboratory rat strains: Long-Evans, Sprague-Dawley, and Wistar. Males and females were socially isolated for either 2h or 48h prior to social play testing and were then exposed to either a familiar (cage mate) or novel playmate, creating four testing conditions: 2h-Familiar, 48h-Familiar, 2h-Novel, and 48h-Novel. Both playmate familiarity and social isolation length influenced social play behavior levels and tactics in juvenile rats, but did so differently for each of the three rat strains. Long-Evans played most with a familiar playmate, irrespective of time isolated, Sprague-Dawley played most in the 48h-Familiar condition, and Wistar played the least in the 2h-Familiar condition, but Wistar played more with a novel playmate than Long-Evans and Sprague-Dawley. Analysis of social play tactics by the playmates in response to nape attacks by the experimental rats revealed strain differences with novel playmates. Here, Sprague-Dawley and Wistar defended more nape attacks than Long-Evans. Sprague-Dawley evaded these attacks, thereby shortening body contact. In contrast, Wistar turned to face their playmate attacker and showed more complete rotations, thereby extending body contact and wrestling longer. Role reversals, which increase social play reciprocity and reflect the quality of social play, were higher in Long-Evans and Sprague-Dawley with familiar playmates. Role reversals decreased for Sprague-Dawley but increased for Wistar after 48h isolation. The effects of playmate familiarity or social isolation length on social play levels and tactics were similar across sex for all three strains. In conclusion, we showed that two common external factors (playmate familiarity and social isolation length) that largely vary across social play studies have a major impact on the level and quality of social play in the three rat strains. Strain differences indicate higher level and quality of social play with familiar playmates in Long-Evans, with familiar playmates after short isolation in Sprague-Dawley, and with novel playmates after longer isolation for Wistar. Future research could determine whether strain differences in neuronal mechanisms underlie these condition-induced variations in social play engagement. Our findings are also informative in suggesting that external conditions like playmate familiarity and social isolation length could influence social play levels and social play quality in typical and atypical children.

Social play behavior is driven by glycine-dependent mechanisms

Social play is pervasive in juvenile mammals, yet it is poorly understood in terms of its underlying brain mechanisms. Specifically, we do not know why young animals are most playful and why most adults cease to social play. Here, we analyze the synaptic mechanisms underlying social play. We found that blocking the rat periaqueductal gray (PAG) interfered with social play. Furthermore, an age-related decrease of neural firing in the PAG is associated with a decrease in synaptic release of glycine. Most importantly, modulation of glycine concentration-apparently acting on the glycinergic binding site of the N-methyl-D-aspartate (NMDA) receptor-not only strongly modulates social play but can also reverse the age-related decline in social play. In conclusion, we demonstrate that social play critically depends on the neurotransmitter glycine within the PAG.

Partnered dance evokes greater intrinsic motivation than home exercise as therapeutic activity for chemotherapy-induced deficits: secondary results of a randomized, controlled clinical trial

Introduction

Dance has been proposed to support superior intrinsic motivation over non-dance forms of therapeutic physical activity. However, this hypothesis has yet to be evaluated empirically, particularly among populations living with neuropathology such as survivors of cancer with neurologic complications from chemotherapy treatment. Questions about motivation are relevant to clinical outcomes because motivation mediates neuroplasticity. We conducted this secondary analysis of a randomized-controlled study to begin to investigate the relationships between personal motivation and neurophysiologic effects of dance-based intervention for healthy aging among populations with neurologic complications of cancer.

Methods

We measured motivation using the Intrinsic Motivation Inventory, a validated patient-reported outcome from the psychological approach of Self Determination Theory. We assessed intrinsic motivation, extrinsic motivation, and satisfaction with intervention within a randomized controlled trial of dance versus exercise designed to alleviate symptoms of chemotherapy-induced impairment. Fifty-two survivors of breast cancer with chemotherapy-induced neuropathy diagnosis and associated sensorimotor functional deficits were randomized (1:1) to 8 weeks of partnered dance or home exercise, performed biweekly (NCT05114005; R21-AG068831).

Results

While satisfaction did not differ between interventions, intrinsic motivation was higher among participants randomized to dance than those randomized to exercise (p < 0.0001 at all timepoints: 2 weeks, 4 weeks, 6 weeks, and 8 weeks of intervention), as was extrinsic motivation at 2 weeks (p = 0.04) and 8 weeks (p = 0.01).

Discussion

These data provide evidence that social dance is more motivating than the type of home exercise generally recommended as therapeutic physical activity. The results inform directions for future study of the effect of dance-based therapeutics on embodied agency, neuroplastic changes, and clinically-relevant neuropathic improvement.

Playfulness and adolescence: mentalization and neuropsychoanalysis perspective

The article attempts at conceptualizing the basic principles of how adolescents develop, getting out of childhood and proceeding to enter young adulthood. The age period of adolescence is marked with intense emotional states, lines of thinking, beliefs and transitions that caregivers often face challenges making sense of or mirroring. Combining mentalization-based approaches with neuropsychoanalytic findings about how basic emotional systems governing playful behavior work can shed additional light into the communication channels and specificities therapists might consider when engaging in such endeavor.

Neonatal treatment with para-chlorophenylalanine (pCPA) induces adolescent hyperactivity associated with changes in the paraventricular nucleus Crh and Trh expressions

Disruption of the brain serotoninergic (5-HT) system during development induces long-lasting changes in molecular profile, cytoarchitecture, and function of neurons, impacting behavioral regulation throughout life. In male and female rats, we investigate the effect of neonatal tryptophan hydroxylase (TPH) inhibition by using para-chlorophenylalanine (pCPA) on the expression of 5-HTergic system components and neuropeptides related to adolescent social play behavior regulation. We observed sex-dependent 5-HT levels decrease after pCPA-treatment in the dorsal raphe nucleus (DRN) at 17 and 35 days. Neonatal pCPA-treatment increased playing, social and locomotory behaviors assessed in adolescent rats of both sexes. The pCPA-treated rats demonstrated decreased Crh (17 days) and increased Trh (35 days) expression in the hypothalamic paraventricular nucleus (PVN). There was sex dimorphism in Htr2c (17 days) and VGF (35 days) in the prefrontal cortex, with the females expressing higher levels of it than males. Our results indicate that neonatal pCPA-treatment results in a long-lasting and sex-dependent DRN 5-HT synthesis changes, decreased Crh, and increased Trh expression in the PVN, resulting in a hyperactivity-like phenotype during adolescence. The present work demonstrates that the impairment of TPH function leads to neurobehavioral disorders related to hyperactivity and impulsivity, such as attention deficit hyperactivity disorder (ADHD).

Resource choice during ontogeny enhances both the short- and longer-term welfare of laying hen pullets

We hypothesised that resource choice during early life contributes to both current and longer-term beneficial effects on animal welfare. We investigated this hypothesis in a longitudinal cross-over experiment with laying hen pullets (Gallus gallus domesticus) reared in pens with one or four litter and perch types, respectively (n = 8 pens/treatment, all providing ample and identical litter and perch space). After 4 weeks (chick period), half the pens were modified to provide the opposite treatment (juvenile period). After 11 more weeks, all groups were moved to novel, identical laying pens (adult period; Week 16-27). In support of our hypothesis, the opportunity to choose between multiple litter and perch variants was associated with higher levels of positively-valenced behaviours, including play as chicks and dustbathing as juveniles and adults, and lower levels of negatively-valenced behaviours, including feather pecking as chicks and juveniles and aggressive pecking as adults. Resource choice in the juvenile period also led to better juvenile and adult plumage condition, and greater growth as adults. We conclude that the opportunity to choose among different litter and perch types, instead of having only one type of each, had both short- and longer-term positive effects on the birds' affective states and physical condition.

MTK, Orlowski SK. Effects of Environmental Enrichments on Welfare and Hepatic Metabolic Regulation of Broiler Chickens

The aims of this study were to find suitable environmental enrichment (EE) and evaluate the combined effect of two EEs, variable light intensity (VL) lighting program and EH, on mental health and hepatic metabolic regulation in commercial broilers. To find the advantageous EEs for broilers, three different EEs (board, hut, and ramp) were tested in trial 1. EEs were placed and the engagement of birds to EEs, dustbathing behavior, and daily physical activity were observed. Birds treated with huts showed higher engagement than the board- or ramp-treated birds (p < 0.05). The results of dustbathing behavior and daily physical activity indicated that the environmental hut (EH) is the most favorable enrichment for broilers. In the second trial, to test the effect of EHs on mental health and hepatic metabolic conditions, the brain and liver were sampled from the four treatment birds (20 lx_Con, 20 lx_Hut, VL_Con and VL_Hut) on day 42. The lower expression of TPH2 (tryptophan hydroxylase 2) of VL_Hut birds than those of VL_Con and 20 lx_Hut treated birds suggests the combining effect of EHs with the VL lighting program on the central serotonergic homeostasis of broilers. Reduced expressions of TH (tyrosine hydroxylase), GR (glucocorticoid receptor), BDNF (brain-derived neurotrophic factor) of VL_Hut treated birds compared to those of VL_Con and 20 lx_Hut birds suggest lower stress, stress susceptibility, and chronic social stress in VL_Hut treated birds. The expression of CPT1A (carnitine palmitoyl transferase 1) increased over three-fold in the liver of VL_Con birds compared to 20 lx_Con birds (p < 0.05). EHs treatment in VL birds (VL_Hut) significantly decreased CPT1A but not in 20 lx birds (20 lx_Hut). The expression of ACCα (acetyl-CoA carboxylase alpha) was significantly decreased in VL_Con birds compared to 20 lx_Con birds. There was no significant difference in the hepatic FBPase (fructose-1,6-bisphosphatase), GR, and 11β-HSD1 (11 β-hydroxysteroid dehydrogenease-1) expression between 20 lx_Con and VL_Con birds, but EHs significantly stimulated GR in 20 lx_Hut birds, and stimulated FBPase and 11β-HSD1 expression in the VL_Hut birds compared to 20 lx_Con birds, suggesting that the VL lighting program reduced fatty acid synthesis and increased fatty acid β-oxidation in the broilers' liver and VL_Hut improved the hepatic de novo glucose production. Taken together, the results suggest that the stimulated voluntary activity by EHs in the light-enriched broiler house improved mental health and hepatic metabolic function of broilers and may indicate that the improved hepatic metabolic function contributes to efficient nutritional support for broilers.

Autogenous cerebral processes: an invitation to look at the brain from inside out

While external stimulation can reliably trigger neuronal activity, cerebral processes can operate independently from the environment. In this study, we conceptualize autogenous cerebral processes (ACPs) as intrinsic operations of the brain that exist on multiple scales and can influence or shape stimulus responses, behavior, homeostasis, and the physiological state of an organism. We further propose that the field should consider exploring to what extent perception, arousal, behavior, or movement, as well as other cognitive functions previously investigated mainly regarding their stimulus-response dynamics, are ACP-driven.

Play and tickling responses map to the lateral columns of the rat periaqueductal gray

The persistence of play after decortication points to a subcortical mechanism of play control. We found that global blockade of the rat periaqueductal gray with either muscimol or lidocaine interfered with ticklishness and play. We recorded vocalizations and neural activity from the periaqueductal gray of young, playful rats during interspecific touch, play, and tickling. Rats vocalized weakly to touch and more strongly to play and tickling. Periaqueductal gray units showed diverse but strong modulation to tickling and play. Hierarchical clustering based on neuronal responses to play and tickling revealed functional clusters mapping to different periaqueductal gray columns. Specifically, we observed play-neutral/tickling-inhibited and tickling/play-neutral units in dorsolateral and dorsomedial periaqueductal gray columns. In contrast, strongly play/tickling-excited units mapped to the lateral columns and were suppressed by anxiogenic conditions. Optogenetic inactivation of lateral periaqueductal columns disrupted ticklishness and play. We conclude that the lateral periaqueductal gray columns are decisive for play and laughter.

Joyful by nature: approaches to investigate the evolution and function of joy in non-human animals

The nature and evolution of positive emotion is a major question remaining unanswered in science and philosophy. The study of feelings and emotions in humans and animals is dominated by discussion of affective states that have negative valence. Given the clinical and social significance of negative affect, such as depression, it is unsurprising that these emotions have received more attention from scientists. Compared to negative emotions, such as fear that leads to fleeing or avoidance, positive emotions are less likely to result in specific, identifiable, behaviours being expressed by an animal. This makes it particularly challenging to quantify and study positive affect. However, bursts of intense positive emotion (joy) are more likely to be accompanied by externally visible markers, like vocalisations or movement patterns, which make it more amenable to scientific study and more resilient to concerns about anthropomorphism. We define joy as intense, brief, and event-driven (i.e. a response to something), which permits investigation into how animals react to a variety of situations that would provoke joy in humans. This means that behavioural correlates of joy are measurable, either through newly discovered 'laughter' vocalisations, increases in play behaviour, or reactions to cognitive bias tests that can be used across species. There are a range of potential situations that cause joy in humans that have not been studied in other animals, such as whether animals feel joy on sunny days, when they accomplish a difficult feat, or when they are reunited with a familiar companion after a prolonged absence. Observations of species-specific calls and play behaviour can be combined with biometric markers and reactions to ambiguous stimuli in order to enable comparisons of affect between phylogenetically distant taxonomic groups. Identifying positive affect is also important for animal welfare because knowledge of positive emotional states would allow us to monitor animal well-being better. Additionally, measuring if phylogenetically and ecologically distant animals play more, laugh more, or act more optimistically after certain kinds of experiences will also provide insight into the mechanisms underlying the evolution of joy and other positive emotions, and potentially even into the evolution of consciousness.

Brief Form of the Affective Neuroscience Personality Scales: Preliminary Psychometric Properties in a European Portuguese Community Sample

Personality theory based on affective neuroscience research suggests the presence of seven affective neurobiological systems. These dimensions have been identified using psychometric instruments such as the Affective Neuroscience Personality Scales (ANPS) and its brief version known as the Brief Affective Neuroscience Personality Scales (BANPS). Despite being a psychometric valid instrument, the BANPS was not adapted to European Portuguese. This study describes a psychometric analysis of the BANPS in a Portuguese population sample. A European Portuguese-speaking sample was recruited (N = 355, Mage = 27.31, DP = 12.75). Confirmatory factor analysis (CFA) was used to confirm the BANPS factorial structure. Pearson correlations were used to explore convergent validity with self-reports for psychological distress and psychopathology. Six factor model was confirmed with adequate goodness-of-fit indices (χ2(449) = 808,9841, TLI = .90, CFI = .92, RMSEA = .048 (.042-.053). Non-agreeable affective systems (anger, fear, distress), correlated positively with psychological distress and symptomology, while play and care systems correlated negatively. Seek and care subscales showed the weakest psychometric properties. The original factor structure was confirmed, suggesting the BANPS may be a valid measure to assess affective behavioral traits in the Portuguese population. Further studies in clinical populations may improve the psychometric data of the BANPS.

Noradrenergic modulation of play in Sprague-Dawley and F344 rats

RATIONALE

For many mammals, engaging in social play behavior as a juvenile is important for cognitive, social, and emotional health as an adult. A playful phenotype reflects a dynamic interplay between genetic framework and experiences that operate on hard-wired brain systems so the relative lack of play in an otherwise playful species may be useful for identifying neural substrates that modulate play behavior. The inbred F344 rat has been identified as a strain that is consistently less playful than other strains commonly used in behavioral research. Norepinephrine (NE) acting on alpha-2 receptors has an inhibitory effect on play and F344 rats differ from a number of other strains in NE functioning. As such, the F344 rat may be particularly useful for gaining insight into NE involvement in play.

OBJECTIVE

The objective of this study was to determine whether the F344 rat is differentially sensitive to compounds that affect NE functioning and that are known to affect play behavior.

METHODS

Using pouncing and pinning to quantify play, the effects of the NE reuptake inhibitor atomoxetine, the NE alpha-2 receptor agonist guanfacine, and the NE alpha-2 receptor antagonist RX821002 on play behavior were assessed in juvenile Sprague-Dawley (SD) and F344 rats.

RESULTS

Atomoxetine and guanfacine reduced play in both SD and F344 rats. RX821002 increased pinning to a comparable extent in both strains but F344 rats were more sensitive to the play-enhancing effects of RX821002 on pounces.

CONCLUSIONS

Strain differences in NE alpha-2 receptor dynamics may contribute to the lower levels of play in F344 rats.

The German version of the brief affective neuroscience personality scales including a LUST scale (BANPS-GL)

Objectives

This study presents the German version of the Brief Affective Neuroscience Personality Scales (BANPS), which includes an additional subscale for the dimension LUST. The BANPS represents a shortened version of the Affective Neuroscience Personality Scales (ANPS), a self-report instrument to assess individual dispositions toward primary emotional systems as proposed by Jaak Panksepp.

Methods

In a large sample (N = 926), the reliability and various facets of validity of the German translation of the BANPS were examined together with the newly included LUST scale. The BANPS-GL was related to the Big Five Inventory (BFI) and Sexual Sensation Seeking Scale (SSSS) and analyzed via confirmatory factor analysis (CFA).

Results

Overall, the BANPS-GL exhibited reliabilities ranging from McDonald's ω = 0.70 (CARE) to α = 0.86 (SADNESS) and plausible correlations with external criteria. For CFA a correlated 7-factor model demonstrated good fit [TLI = 0.95; RMSEA = 0.04 (90% CI: 0.04, 0.05); SRMR = 0.06]. A similar fit was demonstrated for a 2-higher-factor model [TLI = 0.93; RMSEA = 0.05 (90% CI: 0.05, 0.06); SRMR = 0.07].

Conclusion

In broad agreement with the results of the original English version, the BANPS-GL showed good reliability and acceptable factorial validity, and overall improved the psychometric properties of the original long form. Finally, the inclusion of the dimension LUST allows for a complete coverage of the primary emotion dispositions as originally conceptualized by Panksepp.

Liposaccharide-induced sustained mild inflammation fragments social behavior and alters basolateral amygdala activity

RATIONALE

Conditions with sustained low-grade inflammation have high comorbidity with depression and anxiety and are associated with social withdrawal. The basolateral amygdala (BLA) is critical for affective and social behaviors and is sensitive to inflammatory challenges. Large systemic doses of lipopolysaccharide (LPS) initiate peripheral inflammation, increase BLA neuronal activity, and disrupt social and affective measures in rodents. However, LPS doses commonly used in behavioral studies are high enough to evoke sickness syndrome, which can confound interpretation of amygdala-associated behaviors.

OBJECTIVES AND METHODS

The objectives of this study were to find a LPS dose that triggers mild peripheral inflammation but not observable sickness syndrome in adult male rats, to test the effects of sustained mild inflammation on BLA and social behaviors. To accomplish this, we administered single doses of LPS (0-100 μg/kg, intraperitoneally) and measured open field behavior, or repeated LPS (5 μg/kg, 3 consecutive days), and measured BLA neuronal firing, social interaction, and elevated plus maze behavior.

RESULTS

Repeated low-dose LPS decreased BLA neuron firing rate but increased the total number of active BLA neurons. Repeated low-dose LPS also caused early disengagement during social bouts and less anogenital investigation and an overall pattern of heightened social caution associated with reduced gain of social familiarity over the course of a social session.

CONCLUSIONS

These results provide evidence for parallel shifts in social interaction and amygdala activity caused by prolonged mild inflammation. This effect of inflammation may contribute to social symptoms associated with comorbid depression and chronic inflammatory conditions.

Play fighting and the development of the social brain: The rat's tale

The benefits gained by young animals engaging in play fighting have been a subject of conjecture for over a hundred years. Progress in understanding the behavioral development of play fighting and the underlying neurobiology of laboratory rats has produced a coherent model that sheds light on this matter. Depriving rats of typical peer-peer play experience during the juvenile period leads to adults with socio-cognitive deficiencies and these are correlated with physiological and anatomical changes to the neurons of the prefrontal cortex, especially the medial prefrontal cortex. Detailed analysis of juvenile peer play has shown that using the abilities needed to ensure that play fighting is reciprocal is critical for attaining these benefits. Therefore, unlike that which was posited by many earlier hypotheses, play fighting does not train specific motor actions, but rather, improves a skill set that can be applied in many different social and non-social contexts. There are still gaps in the rat model that need to be understood, but the model is well-enough developed to provide a framework for broader comparative studies of mammals from diverse lineages that engage in play fighting.

Enhancing their quality of life: environmental enrichment for poultry

Providing environmental enrichments that increase environmental complexity can benefit poultry welfare. This Poultry Science Association symposium paper is structured around four themes on 1) poultry preferences and affective states 2) species-specific behavior, including play behavior and the relationship between behavior, activity level and walking ability, 3) environmental enrichment and its relationship with indicators of welfare, and 4) a case study focusing on the application of enrichments in commercial broiler chicken production. For effective enrichment strategies, the birds' perspective matters most, and we need to consider individual variation, social dynamics, and previous experience when assessing these strategies. Play behavior can be a valuable indicator of positive affect, and while we do not yet know how much play would be optimal, absence of play suggests a welfare deficit. Activity levels and behavior can be improved by environmental modifications and prior research has shown that the activity level of broilers can be increased, at least temporarily, by increasing the environmental complexity. However, more research on impacts of enrichments on birds' resilience, on birds in commercial conditions, and on slow(er)-growing strains is needed. Finally, incorporating farmers' expertise can greatly benefit enrichment design and implementation on commercial farms.

Perceived Functions of Playfulness in Adult English as a Foreign Language Learners: An Exploratory Study

Influenced by the flowering of positive psychology in the field of foreign language acquisition research in recent years, the present study aimed to explore the perceived functions of playfulness, as a personality construct, among English as a foreign language (EFL) learners. To this aim, an initial sample of 38 EFL learners were selected randomly from the private language institutes of Mashhad, the second largest city in Iran. They were interviewed about any perceived functions of playfulness in the EFL learning context. A qualitative content analysis of the collected data led to the extraction of four categories: Fun and laughter, creativity, mastery orientation, and cultivating relationships. A further in-depth analysis of the categories and comparison with the functions of adult playfulness in psychology (primarily Proyer's 2014 and 2017 works of research) revealed that these four categories can be subsumed under two of the four structural components of adult playfulness; namely, other-directed playfulness and intellectual playfulness. The ability of EFL learners to turn language learning situations, tasks, and environment into enjoyable ones via their playfulness can have implications for the quality of their interpersonal interactions in class and eventually their language proficiency. The findings of this study can pave the way for the translation of the adult playfulness construct from developmental and personality psychology and family relations into the second language acquisition (SLA) domain and its conceptualization in future research in this domain.

Measuring Play Fighting in Rats: A Multilayered Approach

Rough-and-tumble play or play fighting is an important experience in the juvenile period of many species of mammals, as it facilitates the development of social skills, and for some species, play fighting is retained into adulthood as a tool for assessing and managing social relationships. Laboratory rats have been a model species for studying the neurobiology of play fighting and its key developmental and social functions. However, play fighting interactions are complex, involving competition and cooperation; therefore, no single measure to quantify this behavior is able to capture all its facets. Therefore, in this paper, we present a multilayered framework for scoring all the relevant facets of play that can be affected by experimental manipulations and the logic of how to match what is measured with the question being asked. © 2022 Wiley Periodicals LLC.

Towards an expanded neuroscientific understanding of social play

Play has been recognized as a complex and diverse set of behaviors that has been difficult to define. Play can range from rough and tumble play among rats to a human child playing a computer game. Play has been understood to exist in multiple forms such as social, object, and locomotor (Burghardt, 2005). In this article we review the literatures on the neural basis of social play, on heart rate variability, on behavioral switching and set-shifting, on prepulse inhibition of the acoustic startle reflex, and on learning at the level of the basal ganglia. Each of these neuronal pathways, aside from heart rate variability, is rooted in the parafascicular nucleus of the thalamus, an important neural substrate for social play. We argue that social play optimally balances a number of opposing neural pathways by engaging systems involved in safety versus danger (heart rate variability), automatized reactions versus learned reactions to new stimuli (behavioral switching and set-shifting), and gating relevant versus less relevant stimuli (prepulse inhibition of the acoustic startle reflex). The idea that play, in addition to its role in interpersonal adaptation to social life, may have a central role in optimizing flexibility and creativity in individual response to novelty has been explored by previous authors (Huizinga, 1955; Spinka et al., 2001; Pellegrini et al., 2007; Pellis and Pellis, 2017). In this paper we explore the possible underlying neural basis for this function of play, having to do with balancing various neural networks, and in doing so propose an expanded understanding of the nature and function of social play.

Early postnatal hypothyroidism reduces juvenile play behavior, but prenatal hypothyroidism compensates for these effects

Perinatal hypothyroidism causes long-lasting effects on behavior, including hyperactivity, cognitive delays/deficits, and a reduction in anxiety. Although there is some evidence that hypothyroidism during fetal development in humans has been associated with later autism spectrum disorder diagnosis or autism-like traits, the relationships between early thyroid hormones and social behaviors are largely unknown. Previously, we found that a moderate dose of the hypothyroid-inducing drug methimazole during embryonic and postnatal development dramatically increased juvenile play in male and female rats. The goal of the current study was to determine the extent to which thyroid hormones act in prenatal or postnatal development to organize later social behaviors. Subjects were exposed to methimazole in the drinking water during prenatal (embryonic day 12 to birth), postnatal (birth to postnatal day 23), or pre- and postnatal development; control animals received regular drinking water throughout the experiment. They were tested for play behavior as juveniles (P30-32). We found an interaction between pre- and postnatal methimazole administration such that postnatal hypothyroidism decreased some play behaviors, whereas sustained pre- and postnatal hypothyroidism restored play to control levels. The effects were similar in males and females. To our knowledge, this is the first report of an interaction between pre- and postnatal hypothyroidism on later behavior. The complexity of the timing of these effects may help explain why epidemiological studies have not consistently found a relationship between gestational hypothyroidism and later behavior.

EXAMINING THE IMPACT OF NEUROIMMUNE DYSREGULATION ON SOCIAL BEHAVIOR OF MALE AND FEMALE JUVENILE RATS

Many individuals diagnosed with neuropsychiatric disorders, such as autism, attention-deficit/hyperactivity disorder, schizophrenia, and social anxiety disorder, all share a common dimension of aberrant social behavior. Epidemiological data indicate that adverse environmental factors contribute to the risk for neurodevelopmental disorders, including those associated with aberrant social behavior. Early-life exposure to infectious pathogens is one of those adverse environmental factors, suggesting that activation of the immune system during early development may contribute to disease pathology associated with altered social behavior. In the current project, we examined the impact of neonatal infection, with or without juvenile immune activation, on the expression of juvenile social behavior and on the expression of inflammatory cytokines and microglial signaling molecules in the juvenile rat brain. The outcomes of these experiments revealed that neonatal infection significantly decreased juvenile social interaction, but significantly increased juvenile play behavior in male and female rats. Moreover, neonatal infection alone, juvenile immune activation alone, and neonatal infection plus juvenile immune activation all significantly impaired social recognition in juvenile male rats. Juvenile female rats (including controls) failed to demonstrate social recognition as measured in our three-chamber social recognition test. Taken together, the behavioral and molecular data presented here support the sensitivity of the developing brain to immune activation, particularly in the expression of age-appropriate social behaviors. These data warrant the design of additional studies to examine the mechanistic relationship between early-life immune activation and aberrant social behavior to develop novel as well as modify existing therapeutic targets and preventative measures to help those who display aberrant social behavior.

Testing the Associations Between Adult Playfulness and Sensation Seeking: A SEM Analysis of Librarians and Police Officers

Playfulness is an understudied personality trait in adults. We examined the relationships between facets of adult playfulness and sensation seeking (SS) in distant vocational groups, namely, librarians (N = 339) and police officers (N = 399). First, manifest and latent group comparisons (measurement invariance [MI] analysis) showed that police officers were higher in SS than librarians, while we found no group differences for playfulness. Second, structural equation modeling (SEM) analyses showed that playfulness was widely positively related to SS, and findings were replicated across groups. However, the effects were of small to moderate size, and playfulness and SS shared between 4 and 22% variance. Our findings indicate that playfulness is not redundant with SS. Our study extends the understanding of adult playfulness by clarifying its overlap and distinctiveness from SS.

The neuroscience of positive emotions and affect: Implications for cultivating happiness and wellbeing

This review paper provides an integrative account regarding neurophysiological correlates of positive emotions and affect that cumulatively contribute to the scaffolding for happiness and wellbeing in humans and other animals. This paper reviews the associations among neurotransmitters, hormones, brain networks, and cognitive functions in the context of positive emotions and affect. Consideration of lifespan developmental perspectives are incorporated, and we also examine the impact of healthy social relationships and environmental contexts on the modulation of positive emotions and affect. The neurophysiological processes that implement positive emotions are dynamic and modifiable, and meditative practices as well as flow states that change patterns of brain function and ultimately support wellbeing are also discussed. This review is part of "The Human Affectome Project" (http://neuroqualia.org/background.php), and in order to advance a primary aim of the Human Affectome Project, we also reviewed relevant linguistic dimensions and terminology that characterizes positive emotions and wellbeing. These linguistic dimensions are discussed within the context of the neuroscience literature with the overarching goal of generating novel recommendations for advancing neuroscience research on positive emotions and wellbeing.

Synaptic Pruning in Schizophrenia: Does Minocycline Modulate Psychosocial Brain Development?

Recent studies suggest that the tetracycline antibiotic minocycline, or its cousins, hold therapeutic potential for affective and psychotic disorders. This is proposed on the basis of a direct effect on microglia-mediated frontocortical synaptic pruning (FSP) during adolescence, perhaps in genetically susceptible individuals harboring risk alleles in the complement component cascade that is involved in this normal process of CNS circuit refinement. In reviewing this field, it is argued that minocycline is actually probing and modulating a deeply evolved and intricate system wherein psychosocial stimuli sculpt the circuitry of the "social brain" underlying adult behavior and personality. Furthermore, this system can generate psychiatric morbidity that is not dependent on genetic variation. This view has important ramifications for understanding "pathologies" of human social behavior and cognition as well as providing long-sought potential mechanistic links between social experience and susceptibility to mental and physical disease.

Individual differences in social play behaviour predict alcohol intake and control over alcohol seeking in rats

RATIONALE

Social play behaviour is a rewarding social activity displayed by young mammals, thought to be important for the development of brain and behaviour. Indeed, disruptions of social play behaviour in rodents have been associated with cognitive deficits and augmented sensitivity to self-administration of substances of abuse, including alcohol, later in life. However, the relation between social development and loss of control over substance use, a key characteristic of substance use disorders including alcohol use disorder (AUD), has not been investigated. Moreover, it remains unknown how inherent differences in playfulness relate to differences in the sensitivity to substance use and AUD.

OBJECTIVE

The objective of this study is to determine how individual differences in juvenile social play behaviour predict alcohol intake and loss of control over alcohol seeking.

METHODS

Juvenile male Lister hooded rats were characterized for their tendency to engage in social play behaviour. Subsequently, alcohol consumption and conditioned suppression of alcohol seeking were assessed in the tertiles of rats that showed the most and least social play.

RESULTS

The rats that engaged most in social play behaviour consumed more alcohol than their less playful counterparts. However, whereas the most playful rats showed intact conditioned suppression of alcohol seeking, the least playful rats showed no such suppression.

CONCLUSION

Individual levels of playfulness predict the sensitivity to alcohol-directed behaviour. Highly playful rats are more prone to alcohol intake, yet show greater control over alcohol seeking. These findings increase our understanding of the relationship between social development and vulnerability to AUD.

Brain circuits at risk in psychiatric diseases and pharmacological pathways

The multiple brain circuits involved in psychiatric diseases may appear daunting, but we prefer to concentrate on a select few, with a particular sensitivity to stress and neurodevelopmental issues, with a clear pharmacotherapy. This review is structured around 1. the key circuits, their role in health and disease, and the neurotransmitters maintaining them, 2. The influence of upbringing, stress, chronobiology, inflammation and infection, 3. The genetic and epigenetic influence on these circuits, particularly regarding copy number variants and neuronal plasticity, 4. The use and abuse of pharmacological agents with the particular risks of stress and chronobiology at critical periods. A major emphasis is placed on the links between hippocampus, prefrontal cortex and amygdala/periaqueductal grey which control specific aspects of cognition, mood, pain and even violence. Some of the research findings were from the innovative medicine initiative (IMI) NEWMEDS, a 22M€ academic/industrial consortium on the brain circuits critical for psychiatric disease.

Comparison of neurotransmitter levels, physiological conditions, and emotional behavior between isolation-housed rats with group-housed rats

Brain monoaminergic neurotransmitters, such as dopamine (DA), serotonin (5-HT), and noradrenaline (NA), play crucial roles in neuronal and physiological functions, including social behaviors. Isolation housing may induce behavioral and neurochemical abnormalities in rats, although its influence on neurotransmitter levels remains obscure. This study investigated the influence of isolation- or group-housing on core body temperature (T_core ), locomotor activity (ACT), emotional behavior, and neurotransmitter levels in male Wistar rats. Behavioral changes were monitored using the open field test (OFT) and social interaction test (SIT). After 4 weeks, brain tissues were collected to quantify 5-HT, DA, and NA concentrations. Body weight and basal T_core during both the light and dark phase were higher in isolation-housed than in group-housed rats, although no significant difference was seen in ACT. No significant differences were observed during the OFT. Isolation-housed rats showed increased line crossing and decreased social behavior during the SIT. Isolation-housed rats exhibited decreased levels of 5-HT in the caudate putamen and amygdala, and elevated and decreased NA levels in the paraventricular hypothalamic nucleus and hippocampus, respectively. However, DA levels were unaffected. Thus, housing environments may affect brain areas that regulate various neuronal and physiological functions, such as memory, stress responses, and emotional behavior.

II. Antidepressants and sexual behavior: Acute fluoxetine, but not ketamine, disrupts paced mating behavior in sexually experienced female rats

Female sexual dysfunction is both a symptom of depression and exacerbated by treatments for depression. Ketamine, a novel treatment for depression, has been shown to enhance, whereas fluoxetine has been shown to impair sexual motivation. Sexual experience leads to more robust partner preference and paced mating behavior in female rats. Whether acute ketamine and fluoxetine similarly affect sexual motivation and mating behavior in sexually experienced female rats is unknown. Sexually experienced female rats received 10 mg/kg i.p. of ketamine or saline vehicle (Experiment 1) or 10 mg/kg i.p. of fluoxetine or water vehicle (Experiment 2) 30 min before a 10-min no-contact partner preference test followed immediately by a 15-intromission paced mating test. Partner preference and paced mating behavior did not differ between ketamine- and saline-treated rats. In contrast, rats treated with fluoxetine spent significantly less time with either stimulus animal and were less active during the partner preference test than water-treated rats. Additionally, contact-return latency to ejaculation was significantly longer in fluoxetine-treated rats and they spent less time with the male during paced mating in comparison to water-treated rats. Thus, even with sexual experience, fluoxetine disrupts sexual function whereas ketamine has no detrimental effects on sexual behavior in female rats. A growing body of evidence suggests that ketamine is an encouraging new approach to treat depression particularly because it is not associated with sexual dysfunction.

Can the frequency of defensive posture adoption influence the expression of active behavior of adult rats?

During the youth, rats spend a long time in play fighting (PF), and asymmetries are observed in terms of the frequency of adoption of the supine posture. This study investigated the effects of asymmetry in adopting supine posture during PF on the time spent in locomotor activity-related contextual behaviors during youth and adulthood. Male Wistar rats were divided into three groups according to the number of times of their adoption of a defensive supine (S) posture: low (LS, n = 10), intermediary (IS, n = 10) and high (HS, n = 10). Rats aged 21-62 days were placed in voluntary physical active cages (VPAC) with running wheels. The time spent in social play (SP), play fighting (PF), voluntary physical activity (VPA), spontaneous physical activity (SPA) and resting (Rest) were recorded daily. During adulthood (63-92 days of age), rats were placed individually in the VPAC, with daily quantification of VPA. The average time spent in PF was not different among the groups, but was age-dependent. LS and IS rats spent more time in VPA than the HS rats, between days 49-62 (intragroup analyses) and 72-78 (individual analyses) days of age. However, LS and IS animals spent less time in SPA than HS rats from 42-48 days of age. In conclusion, the expressions of VPA and SPA are influenced by the asymmetries in adoption of the supine posture of members within a social group, remaining even after the separation of the social groups.

Methamphetamine exposure during the first, but not the second half of prenatal development, affects social play behavior

Methamphetamine (MA), as a psychostimulant drug that crosses the placental barrier, may disrupt the development of social play. The present study aims to examine the effect of prenatal MA (5 mg/kg) exposure during the first (gestational day (GD) 1-11) or second (GD 12-22) halves of prenatal development of rats on social play behavior. To investigate an acute effect of MA on social play in adulthood, juvenile rats were exposed to a dose of 1 mg/kg MA or saline on the test day and tested for social play for 15 min. Prenatal exposure to MA during GD 1-11 increased social play behavior during 5-10 min interval of the test in males but not females. Prenatal MA during GD 12-22 did not influence social play in males nor females. However, social play occurred to a greater extent in GD 12-22 groups compared with GD 1-11. Acute exposure to MA eliminated playful behavior in all groups and decreased social exploration in GD 1-11. Our results suggest that manipulation of prenatal development during the first half of the gestational period has a greater impact on social play behavior than during the second half.

How strain differences could help decipher the neurobiology of mammalian playfulness: What the less playful Fischer 344 rat can tell us about play

Play is common among the young of many mammalian species. How that play is exhibited results from a dynamic interplay between genetic framework and experiential influences that, in turn, operate on hard-wired brain systems. One approach towards understanding how genes and environment interact with brain substrates to yield a particular playful phenotype is to take advantage of inbred strains of rats that come with a known genetic identity and assess the effects of varying early social experiences and targeted neurobiological interventions on rats of these strains. This paper primarily summarizes research utilizing the F344 inbred strain, a rat that consistently plays less than most other strains.

Effect of a social peer on risky decision making in male Sprague Dawley rats

Adolescence is a period associated with increased risk taking and peer relations. Research has shown that age is correlated with vulnerability to peer pressure, with youth being more influenced by peers compared with adults, leading to exacerbated risk taking, including risk for drug abuse. Preclinical research suggests that these findings may also be applicable to rodents, as younger rats find social interaction rewarding and are prone to risky behavior. However, there is little research on the effect of social interaction on rodent models of risky decision making. This study examined risky decision making utilizing a dual-compartment apparatus that consisted of two adjacent operant conditioning chambers separated by a wire mesh screen partition that allowed for limited social interaction. Male rats performed a risky decision making task in which they had a choice between a small reinforcer and larger reinforcer that was associated with a mild footshock, which increased in probability across the session. Rats were initially trained during adolescence and performance on the task was assessed in the presence or absence of a peer in the adjacent chamber during young adulthood. Results revealed that there was less risk discounting, leading to greater preference for the larger, risky reinforcer, in rats that had daily exposure to a social peer during training. These results provide evidence that social influence on risk taking can be modeled in rats, perhaps having implications for drug abuse risk. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Unidirectional opioid-cannabinoid cross-tolerance in the modulation of social play behavior in rats

RATIONALE

The endocannabinoid and the endogenous opioid systems interact in the modulation of social play behavior, a highly rewarding social activity abundantly expressed in young mammals. Prolonged exposure to opioid or cannabinoid receptor agonists induces cross-tolerance or cross-sensitization to their acute behavioral effects.

OBJECTIVES AND METHODS

Behavioral and biochemical experiments were performed to investigate whether cross-tolerance or cross-sensitization occurs to the play-enhancing effects of cannabinoid and opioid drugs on social play behavior, and the possible brain substrate involved.

RESULTS

The play-enhancing effects induced by systemic administration of JZL184, which inhibits the hydrolysis of the endocannabinoid 2-AG, were suppressed in animals repeatedly pretreated with the opioid receptor agonist morphine. Conversely, acute morphine administration increased social play in rats pretreated with vehicle or with either JZL184 or the cannabinoid agonist WIN55,212-2. Acute administration of JZL184 increased the activation of both CB1 receptors and their effector Akt in the nucleus accumbens and prefrontal cortex, brain regions important for the expression of social play. These effects were absent in animals pretreated with morphine. Furthermore, only animals repeatedly treated with morphine and acutely administered with JZL184 showed reduced activation of CB1 receptors and Akt in the amygdala.

CONCLUSIONS

The present study demonstrates a dynamic opioid-cannabinoid interaction in the modulation of social play behavior, occurring in limbic brain areas strongly implicated in social play behavior. A better understanding of opioid-cannabinoid interactions in social play contributes to clarify neurobiological aspects of social behavior at young age, which may provide new therapeutic targets for social dysfunctions.

From adolescence to late aging: A comprehensive review of social behavior, alcohol, and neuroinflammation across the lifespan

The passage of time dictates the pace at which humans and other organisms age but falls short of providing a complete portrait of how environmental, lifestyle and underlying biological processes contribute to senescence. Two fundamental features of the human experience that change dramatically across the lifespan include social interactions and, for many, patterns of alcohol consumption. Rodent models show great utility for understanding complex interactions among aging, social behavior and alcohol use and abuse, yet little is known about the neural changes in late aging that contribute to the natural decline in social behavior. Here, we posit that aging-related neuroinflammation contributes to the insipid loss of social motivation across the lifespan, an effect that is exacerbated by patterns of repeated alcohol consumption observed in many individuals. We provide a comprehensive review of (i) neural substrates crucial for the expression of social behavior under non-pathological conditions; (ii) unique developmental/lifespan vulnerabilities that may contribute to the divergent effects of low-and high-dose alcohol exposure; and (iii) aging-associated changes in neuroinflammation that may sit at the intersection between social processes and alcohol exposure. In doing so, we provide an overview of correspondence between lifespan/developmental periods between common rodent models and humans, give careful consideration to model systems used to aptly probe social behavior, identify points of coherence between human and animal models, and point toward a multitude of unresolved issues that should be addressed in future studies. Together, the combination of low-dose and high-dose alcohol effects serve to disrupt the normal development and maintenance of social relationships, which are critical for both healthy aging and quality of life across the lifespan. Thus, a more complete understanding of neural systems-including neuroinflammatory processes-which contribute to alcohol-induced changes in social behavior will provide novel opportunities and targets for promoting healthy aging.

The cross-cultural expression of internet gaming distress in North America, Europe, and China

We compare the forms online gaming-related distress takes cross-culturally, and examine how much such distress resembles the World Health Organization's (WHO) “Gaming disorder,” understood to be an “addiction.” Our preliminary exploratory factor analysis (EFA) in North America (n = 2025), Europe (n = 1198), and China (n = 841) revealed a constant four-factor structure across the three regions, with classic “addiction” symptoms always clustering together on the first and most important factor, though with some variability in regional factors' exact item composition. In the present study, we use second-order confirmatory factor analysis (CFA) to further examine this factor structure and the cultural similarities and differences. Specifically, we focus on confirming the regional structure and composition of an ethnographically developed 21-item gaming distress scale, which contains a wider symptoms pool than typical gaming disorder scales, and thus allows us to better separate generalized gaming distress's “addictive” from other culturally-influenced “problem” experiences and behaviors in each regional case. We use propensity score matching to separate the impact on gaming-related distress of regional culture from demographic variables (North America/Europe: n = 1043 pairs; North America/China: n = 535 pairs). Although our results support current WHO formulations of gaming-related distress as an addictive disorder, we show how cultural forces can shape how “addictive” and “problem” gaming are experienced and thus psychiatrically presented in different parts of the world. In particular, generalized gaming distress's addictive and problematic dimensions seem to be shaped by culture-specific expressions of achievement motivations, social connection and disconnection, and unique psychosomatic experiences.

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Second-order CFA shows similarities and differences between online gaming distress in North America, Europe, and China.

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Our 21-item distress scale allows us to separate “addictive” from “problem” experiences and behaviors in each regional case.

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Propensity score matching helps us separate the impact on gaming distress of regional culture from demographic variables.

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Generalized gaming distress consists of four dimensions, with three closely related to addiction experiences and behaviors.

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Our results support current WHO and APA formulations of gaming-related distress as an addictive disorder.

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Culture also shapes how “addictive” and “problem” gaming are experienced in different parts of the world.

Basal ganglia involvement in the playfulness of juvenile rats

Play is an important part of normal childhood development and can be readily studied in the laboratory rat in the form of rough-and-tumble play. Given the robust nature of rough-and-tumble play, it has often been assumed that the basal ganglia would have a prominent role in modulating this behavior. Recent work using c-fos expression as a metabolic marker for neural activity combined with temporary inactivation of relevant corticostriatal regions and pharmacological manipulations of opioid, cannabinoid, and dopamine systems has led to a better understanding of how basal ganglia circuitry may be involved in modulating social play in the juvenile rat. Studies using selective play deprivation have also provided insight into the consequences of playful experiences on basal ganglia function. Data reviewed in this paper support a role for the basal ganglia in social play and also suggest that corticostriatal functioning also benefits from playful activities.

Distinguishing Core from Peripheral Psychiatric Symptoms: Addictive and Problematic Internet Gaming in North America, Europe, and China

We explore the problem of distinguishing the relatively constant versus culturally variable dimensions of mental suffering and disorder in the context of a cross-cultural study of Internet gaming-related distress. We extend the conceptual contrast of "core" and "peripheral" symptoms drawn from game studies and use a framework that synthesizes cultural and neurobiological understandings of emotional distress. In our framework, "core" symptoms are relatively constant across cultures and therefore presumed to be more closely tied to a neurobiological base. By contrast, we treat as "peripheral" symptoms those that are more culturally variable, and thus less directly tied to the neurobiology of addiction. We develop and illustrate this approach with a factor analysis of cross-cultural survey data, resting on previous ethnographic work, through which we compare online gaming distress experienced in North America (n = 2025), Europe (n = 1198), and China (n = 841). We identify the same four-factor structure across the three regions, with Addiction always the first and most important factor, though with variability in regional factors' exact item composition. The study aims to advance an integrative biocultural approach to distinguishing universal as opposed to culturally contingent dimensions of human suffering, and to help resolve debates about whether problem gaming represents a form of addiction.

Does Anhedonia Presage Increased Risk of Posttraumatic Stress Disorder? : Adolescent Anhedonia and Posttraumatic Disorders

Anhedonia, the reduced ability to experience pleasure, is a dimensional entity linked to multiple neuropsychiatric disorders, where it is associated with diminished treatment response, reduced global function, and increased suicidality. It has been suggested that anhedonia and the related disruption in reward processing may be critical precursors to development of psychiatric symptoms later in life. Here, we examine cross-species evidence supporting the hypothesis that early life experiences modulate development of reward processing, which if disrupted, result in anhedonia. Importantly, we find that anhedonia may confer risk for later neuropsychiatric disorders, especially posttraumatic stress disorder (PTSD). Whereas childhood trauma has long been associated with increased anhedonia and increased subsequent risk for trauma-related disorders in adulthood, here we focus on an additional novel, emerging direct contributor to anhedonia in rodents and humans: fragmented, chaotic environmental signals ("FRAG") during critical periods of development. In rodents, recent data suggest that adolescent anhedonia may derive from aberrant pleasure/reward circuit maturation. In humans, recent longitudinal studies support that FRAG is associated with increased anhedonia in adolescence. Both human and rodent FRAG exposure also leads to aberrant hippocampal function. Prospective studies are underway to examine if anhedonia is also a marker of PTSD risk. These preliminary cross-species studies provide a critical construct for future examination of the etiology of trauma-related symptoms in adults and for and development of prophylactic and therapeutic interventions. In addition, longitudinal studies of reward circuit development with and without FRAG will be critical to test the mechanistic hypothesis that early life FRAG modifies reward circuitry with subsequent consequences for adolescent-emergent anhedonia and contributes to risk and resilience to trauma and stress in adulthood.

Opioid modulation of social play reward in juvenile rats

Social play behaviour is a vigorous form of social interaction abundant during the juvenile and adolescent phases of life in many mammalian species, including rats and humans. Social play is thought to be important for social, emotional and cognitive development. Being a rewarding activity, the expression of social play depends on its pleasurable and motivational properties. Since opioids have been widely implicated in reward processes, in the present study we investigated the role of opioids in the pleasurable and motivational properties of social play behaviour in rats. To assess social play motivation, an operant conditioning setup was used in which rats responded for social play under a progressive ratio schedule of reinforcement. Treatment with the opioid receptor agonist morphine reduced responding for social play at the highest dose tested, likely due to its rate-limiting effects. Morphine treatment increased the expression of social play behaviour during reinforced periods. The acquisition of social play-induced conditioned place preference (CPP) in a subeffective conditioning protocol was enhanced by treatment with morphine. Morphine treatment alone also induced CPP. In contrast, antagonizing opioid receptors with naloxone reduced responding for social play, the expression of social play and blocked the development of social play-induced CPP. These data implicate opioid neurotransmission in both the pleasurable and the motivational aspects of social play behaviour in rats. This article is part of the Special Issue entitled 'The neuropharmacology of social behavior: from bench to bedside'.

A possible social relative reward effect: Influences of outcome inequity between rats during operant responding

Social interactions/situations have dramatic influences on motivation. Creating animal models examining these influences promotes a better understanding of the psychological and biological underpinnings of social motivation. Rodents are sensitive to social history/experience during associative conditioning and food-sharing tasks. Would reward-oriented operant behavior be sensitive to social influences by showing a negative contrast-like effect when another organism obtains a greater value outcome? We used a side-by-side arrangement of operant response chambers wherein one animal obtained consistently high reward signaled by a discrete cue. The neighboring, experimental rat experienced different combinations of high and low reward trial sequences. Control conditions included distraction from a conspecific in the neighboring chamber (rat distractor) or cue/food dispenser operating without a conspecific (program distractor) in addition to testing subjects alone. Results support an influence of the other animal actively performing the task on the experimental subject's behavior. Primarily, responding was significantly slower for the low reward trials while the neighboring rat was receiving the higher magnitude reward. The lever-press and not food-cup retrieval latency was significantly slower during exposure to a conspecific neighbor performing the operant task. The effect was not obtained in all session sequences and was more pronounced using longer series of consecutive low reward trials. The slowing effect was also obtained with the program-distractor experience in a different trial sequence. These findings suggest a social-induced negative incentive contrast effect in rats possibly mediated by an outcome inequity process that could have key similarities to complex situational-affective effects on motivation involving frustration or jealously.

Social genomics of healthy and disordered internet gaming

OBJECTIVES

To combine social genomics with cultural approaches to expand understandings of the somatic health dynamics of online gaming, including in the controversial nosological construct of internet gaming disorder (IGD).

METHODS

In blood samples from 56 U.S. gamers, we examined expression of the conserved transcriptional response to adversity (CTRA), a leukocyte gene expression profile activated by chronic stress. We compared positively engaged and problem gamers, as identified by an ethnographically developed measure, the Positive and Negative Gaming Experiences Scale (PNGE-42), and also by a clinically derived IGD scale (IGDS-SF9).

RESULTS

CTRA profiles showed a clear relationship with PNGE-42, with a substantial linkage to offline social support, but were not meaningfully associated with disordered play as measured by IGDS-SF9.

CONCLUSIONS

Our study advances understanding of the psychobiology of play, demonstrating via novel transcriptomic methods the association of negatively experienced internet play with biological measures of chronic threat, uncertainty, and distress. Our findings are consistent with the view that problematic patterns of online gaming are a proxy for broader patterns of biopsychosocial stress and distress such as loneliness, rather than a psychiatric disorder sui generis, which might exist apart from gamers' other life problems. By confirming the biological correlates of certain patterns of internet gaming, culturally-sensitive genomics approaches such as this can inform both evolutionary theorizing regarding the nature of play, as well as current psychiatric debates about the appropriateness of modeling distressful gaming on substance addiction and problem gambling.

Toward a Neuroscientific Understanding of Play: A Dimensional Coding Framework for Analyzing Infant-Adult Play Patterns

Play during early life is a ubiquitous activity, and an individual’s propensity for play is positively related to cognitive development and emotional well-being. Play behavior (which may be solitary or shared with a social partner) is diverse and multi-faceted. A challenge for current research is to converge on a common definition and measurement system for play – whether examined at a behavioral, cognitive or neurological level. Combining these different approaches in a multimodal analysis could yield significant advances in understanding the neurocognitive mechanisms of play, and provide the basis for developing biologically grounded play models. However, there is currently no integrated framework for conducting a multimodal analysis of play that spans brain, cognition and behavior. The proposed coding framework uses grounded and observable behaviors along three dimensions (sensorimotor, cognitive and socio-emotional), to compute inferences about playful behavior in a social context, and related social interactional states. Here, we illustrate the sensitivity and utility of the proposed coding framework using two contrasting dyadic corpora (N = 5) of mother-infant object-oriented interactions during experimental conditions that were either non-conducive (Condition 1) or conducive (Condition 2) to the emergence of playful behavior. We find that the framework accurately identifies the modal form of social interaction as being either non-playful (Condition 1) or playful (Condition 2), and further provides useful insights about differences in the quality of social interaction and temporal synchronicity within the dyad. It is intended that this fine-grained coding of play behavior will be easily assimilated with, and inform, future analysis of neural data that is also collected during adult–infant play. In conclusion, here, we present a novel framework for analyzing the continuous time-evolution of adult–infant play patterns, underpinned by biologically informed state coding along sensorimotor, cognitive and socio-emotional dimensions. We expect that the proposed framework will have wide utility amongst researchers wishing to employ an integrated, multimodal approach to the study of play, and lead toward a greater understanding of the neuroscientific basis of play. It may also yield insights into a new biologically grounded taxonomy of play interactions.

Effects of neonatal handling on play and anxiety in F344 and Lewis rats

Play is an important part of normal childhood development and seen in many mammals, including rats. To better understand the interplay between genotype and postnatal experiences, the effects of neonatal handling on play were assessed in Lewis (LEW) and Fischer 344 (F344) rats. Handled litters experienced brief periods of separation during the first two postnatal weeks. F344 rats were less likely to direct nape contacts toward an untreated Sprague-Dawley (SD) partner and less likely to rotate to a supine position in response to a nape contact. When compared to rats from control litters, handled LEW, and F344 rats were more likely to respond to nape contacts with complete rotations, suggesting that handling increased playful responsiveness to a comparable extent in both strains. SD rats paired with handled inbred rats had more nape contacts than those paired with non-handled rats. While handled LEW rats also tended to direct more nape contacts to the SD partner than non-handled LEW rats there was no difference between handled and non-handled F344 rats. These results could not be readily explained by handling-induced changes in either maternal care or anxiety. These data suggest that the behavioral consequences of neonatal handling may not depend to a great extent on the genetic platform that these manipulations are acting on. These data also suggest that the ability to maintain the ebb and flow between playful solicitation and playful responsiveness may be compromised in F344 rats and may contribute to the lower levels of play in this strain.