Parent-child physiological concordance predicts stronger observational fear learning in children with a less secure relationship with their parent.

Observational fear learning is common in children as they learn to fear by observing their parents. Although adaptive, it can also contribute to the development of fear-related psychopathologies such as anxiety disorders. Therefore, it is important to identify and study the factors that modulate children's sensitivity to observational fear learning. For instance, observational fear learning can be facilitated by the synchronization of biological systems between two people. In parent-child dyads, physiological concordance is important and varies according to the attachment relationship, among others. We investigated the joint effect of parent-child physiological concordance and attachment on observational fear learning in children. A total of 84 parent-child dyads participated in this study. Parents were filmed while exposed to a fear-conditioning protocol, where one stimulus was associated with a shock (CS+) and the other was not (CS-). This recording was then shown to the children (observational learning). Thereafter, both stimuli (CS+ and CS-) were presented to the children without any shock (direct expression test). For both the parent and child, skin conductance activity was recorded throughout the entire procedure. We measured physiological concordance between the parent's phasic skin conductance signal during conditioning and the child's signal during the observational learning stage. Children showing stronger concordance and a less secure relationship with their parent exhibited higher levels of fear to the CS+, as indicated by a heightened skin conductance response during the direct expression test. Thus, when children have an insecure relationship with their parent, strong physiological concordance may increase their sensitivity to observational fear learning.

Learning about threat from friends and strangers is equally effective: An fMRI study on observational fear conditioning.

Humans often benefit from social cues when learning about the world. For instance, learning about threats from others can save the individual from dangerous first-hand experiences. Familiarity is believed to increase the effectiveness of social learning, but it is not clear whether it plays a role in learning about threats. Using functional magnetic resonance imaging, we undertook a naturalistic approach and investigated whether there was a difference between observational fear learning from friends and strangers. Participants (observers) witnessed either their friends or strangers (demonstrators) receiving aversive (shock) stimuli paired with colored squares (observational learning stage). Subsequently, participants watched the same squares, but without receiving any shocks (direct-expression stage). We observed a similar pattern of brain activity in both groups of observers. Regions related to threat responses (amygdala, anterior insula, anterior cingulate cortex) and social perception (fusiform gyrus, posterior superior temporal sulcus) were activated during the observational phase, possibly reflecting the emotional contagion process. The anterior insula and anterior cingulate cortex were also activated during the subsequent stage, indicating the expression of learned threat. Because there were no differences between participants observing friends and strangers, we argue that social threat learning is independent of the level of familiarity with the demonstrator.

Autism Spectrum Disorder Model Mice Induced by Prenatal Exposure to Valproic Acid Exhibit Enhanced Empathy-Like Behavior via Oxytocinergic Signaling.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by core symptoms, including impairments in social behavior and repetitive interests. Recent studies have revealed that individuals with ASD also display decreased empathy, ultimately leading to difficulties in social relationships; however, another report indicated that individuals with ASD have enhanced emotional empathy. Nonetheless, the neurobiological mechanisms underlying altered empathy in individuals with ASD remain unclear. In this study, we assessed empathy-like behaviors in valproic acid (VPA)-treated mice-a mouse model of ASD with observational fear learning. We then investigated the brain regions and signaling systems responsible for the altered empathy-like behaviors in VPA-treated mice. As a result, mice prenatally exposed to VPA displayed increased empathy-like behaviors, which were not attributed to altered sensitivity to auditory stimuli or enhanced memory for pain-related contexts. Immunohistochemical analysis revealed that the number of c-Fos positive oxytocinergic neurons in the paraventricular nucleus of the hypothalamus (PVN) was significantly higher in VPA-treated mice after observational fear learning. Finally, we found that pretreatment with L-368899, an antagonist of the oxytocin receptor, repressed the empathetic behavior in VPA-treated mice. These results suggest that VPA-treated ASD model animals showed increased emotional empathy-like behaviors through the hyperactivation of PVN oxytocinergic neurons for the first time. Further investigation of this hyperactivity will help to identify extrinsic stimuli and the condition which are capable of activation of PVN oxytocinergic neurons and to identify novel approach to enhance oxytocin signaling, which ultimately pave the way to development of novel therapy for ASD.

Conformity-like behaviour in mice observing the freezing of other mice: a model of empathy.

BACKGROUND: Empathy refers to the ability to recognise and share emotions with others. Several research groups have recognised observational fear in mice as a useful behavioural model for assessing their ability to empathise. However, in these observation systems, it remains unclear whether the observer mouse truly recognises the movements of, and empathises with, the demonstrator mouse. We examined changes in the behaviour of an observer mouse when a demonstrator mouse was anaesthetised, when the demonstrator's activity was increased, and when the interval of electrical stimulation was altered. If mice exhibit an ability to empathise, then the observer should display empathic behaviour when the demonstrator experiences pain or discomfort under any circumstances. RESULTS: Relative to low-frequency stimulation, frequent electrical stimulation reduced immobility time among observer mice. Moreover, when demonstrators exhibited excessive activity, the activity of the observers significantly increased. In addition, the proportion of immobility time among observer mice significantly increased when demonstrator mice exhibited fear learning and excessive immobility. CONCLUSION: Although our results indicate that observer mice change their behaviour based on the movements of demonstrator mice, increases in immobility time may reflect conformity-like behaviour rather than emotional empathy. Thus, not only visual but also auditory and odour information additionally influenced the conformity-like behaviour shown by observer mice. Thus, our findings suggest that methods other than the fear observation system should be used to investigate rodent empathy-like behaviour.

Rodent models for studying empathy.

Empathy is the important capacity to recognize and share emotions with others. Recent evidence shows that rodents possess a remarkable affective sensitivity to the emotional state of others and that primitive forms of empathy exist in social lives of rodents. However, due to the ambiguous definitional boundaries between empathy, emotional contagion and other related terms, distinct components of empathic behaviors in rodents need to be clarified. Hence, we review recent experimental studies demonstrating that rodents are able to share emotions with others. Specifically, we highlight several behavioral models that examine different aspects of rodent empathic behaviors in response to the various distress of conspecifics. Experimental approaches using rodent behavioral models will help elucidate the neural circuitry of empathy and its neurochemical association. Integrating these findings with corresponding experiments in humans will ultimately provide novel insights into therapeutic interventions for mental disorders associated with empathy.

Witnessed trauma exposure induces fear in mice through a reduction in endogenous neurosteroid synthesis.

Neurosteroids have been implicated in the pathophysiology of post-traumatic stress disorder (PTSD). Allopregnanolone is reduced in subsets of individuals with PTSD and has been explored as a novel treatment strategy. Both direct trauma exposure and witnessed trauma are risk factors for PTSD; however, the role of neurosteroids in the behavioral outcomes of these unique experiences has not been explored. Here, we investigate whether observational fear is associated with a reduced capacity for endogenous neurosteroidogenesis and the relationship with behavioral outcomes. We demonstrated that mice directly subjected to a threat (foot shocks) and those witnessing the threat have decreased plasma levels of allopregnanolone. The expression of a key enzyme involved in endogenous neurosteroid synthesis, 5α-reductase type 2, is decreased in the basolateral amygdala, which is a major emotional processing hub implicated in PTSD. We demonstrated that genetic knockdown or pharmacological inhibition of 5α-reductase type 2 exaggerates the behavioral expression of fear in response to witnessed trauma, whereas oral treatment with an exogenous, synthetic neuroactive steroid gamma-aminobutyric acid-A receptor positive allosteric modulator with molecular pharmacology similar to allopregnanolone (SGE-516 [tool compound]) decreased the behavioral response to observational fear. These data implicate impaired endogenous neurosteroidogenesis in the pathophysiology of threat exposure, both direct and witnessed. Further, these data suggest that treatment with exogenous 5α-reduced neurosteroids or targeting endogenous neurosteroidogenesis may be beneficial for the treatment of individuals with PTSD, whether resulting from direct or witnessed trauma.

Oxytocin receptor control social information about fear expression of others in mice.

The social functions of oxytocin are diverse, and the specific aspects of information processing involved in emotional contagion remain unclear. We compared some fear-related behaviors among oxytocin receptor knockout mice and oxytocin-receptor-reduced mice with that of wild-type mice. In the observational fear assay, which reflects fear emotional contagion, mice that observed other individuals receiving electric shocks exhibited vicarious freezing. Mice with reduced or knockout oxytocin receptor expression showed reduced vicarious freezing. In the emotional discrimination assay, which reflects the ability to perceive others' emotional cues, we compared approach and scent-sniffing behaviors toward fear and emotionally neutral individuals. While wild-type mice were able to detect the fear emotion of others, mice with reduced or knocked-out oxytocin receptors showed reduced discrimination ability. In the fear behavior assays, which do not present social cues, we did not find these differences in oxytocin receptor expression in the brain. These findings indicate that oxytocin plays a role in emotional contagion by perceiving the emotions of others.

A threat from within: Learning to fear by observing aversive bodily symptoms in others.

Although observational fear learning has been implicated in the development of phobic-related fears, studies investigating observational learning of fear of bodily symptoms remain scarce. Therefore, the aim of the present study was to investigate whether fear in response to bodily symptoms can be acquired simply by observing a fearful reaction to provocation of aversive bodily symptoms in others. Forty healthy participants underwent an observational fear conditioning paradigm consisting of two phases. In the first phase, participants observed a demonstrator reacting to an aversive bodily symptom provocation (unconditioned stimulus or US, i.e., labored breathing) paired with one conditioned stimulus (CS+) but not with the other one (CS-, both CSs were geometric symbols presented on a screen the demonstrator was watching). In the second phase, participants were directly presented with the same conditioned stimuli, but in the absence of the US. Our results revealed enhanced conditioned fear responses in the beginning of the second phase to the CS + as compared to CS-, as indexed by greater skin conductance and subjective fear responses, as well as greater potentiation of startle eyeblink responses to the CS + as compared to the ITI. Taken together, these findings implicate that fear of bodily symptoms can be learned through observation of others, that is, without first-hand experience of bodily threat.

ARNT2 controls prefrontal somatostatin interneurons mediating affective empathy.

Empathy, crucial for social interaction, is impaired across various neuropsychiatric conditions. However, the genetic and neural underpinnings of empathy variability remain elusive. By combining forward genetic mapping with transcriptome analysis, we discover that aryl hydrocarbon receptor nuclear translocator 2 (ARNT2) is a key driver modulating observational fear, a basic form of affective empathy. Disrupted ARNT2 expression in the anterior cingulate cortex (ACC) reduces affect sharing in mice. Specifically, selective ARNT2 ablation in somatostatin (SST)-expressing interneurons leads to decreased pyramidal cell excitability, increased spontaneous firing, aberrant Ca2+ dynamics, and disrupted theta oscillations in the ACC, resulting in reduced vicarious freezing. We further demonstrate that ARNT2-expressing SST interneurons govern affective state discrimination, uncovering a potential mechanism by which ARNT2 polymorphisms associate with emotion recognition in humans. Our findings advance our understanding of the molecular mechanism controlling empathic capacity and highlight the neural substrates underlying social affective dysfunctions in psychiatric disorders.

Dual circuits originating from the ventral hippocampus independently facilitate affective empathy.

Affective empathy enables social mammals to learn and transfer emotion to conspecifics, but an understanding of the neural circuitry and genetics underlying affective empathy is still very limited. Here, using the naive observational fear between cagemates as a paradigm similar to human affective empathy and chemo/optogenetic neuroactivity manipulation in mouse brain, we investigate the roles of multiple brain regions in mouse affective empathy. Remarkably, two neural circuits originating from the ventral hippocampus, previously unknown to function in empathy, are revealed to regulate naive observational fear. One is from ventral hippocampal pyramidal neurons to lateral septum GABAergic neurons, and the other is from ventral hippocampus pyramidal neurons to nucleus accumbens dopamine-receptor-expressing neurons. Furthermore, we identify the naive observational-fear-encoding neurons in the ventral hippocampus. Our findings highlight the potentially diverse regulatory pathways of empathy in social animals, shedding light on the mechanisms underlying empathy circuity and its disorders.

Understanding Others' Distress Through Past Experiences: The Role of Memory Engram Cells in Observational Fear.

For individuals to survive and function in society, it is essential that they recognize, interact with, and learn from other conspecifics. Observational fear (OF) is the well-conserved empathic ability of individuals to understand the other's aversive situation. While it is widely known that factors such as prior similar aversive experience and social familiarity with the demonstrator facilitate OF, the neural circuit mechanisms that explicitly regulate experience-dependent OF (Exp OF) were unclear. In this review, we examine the neural circuit mechanisms that regulate OF, with an emphasis on rodent models, and then discuss emerging evidence for the role of fear memory engram cells in the regulation of Exp OF. First, we examine the neural circuit mechanisms that underlie Naive OF, which is when an observer lacks prior experiences relevant to OF. In particular, the anterior cingulate cortex to basolateral amygdala (BLA) neural circuit is essential for Naive OF. Next, we discuss a recent study that developed a behavioral paradigm in mice to examine the neural circuit mechanisms that underlie Exp OF. This study found that fear memory engram cells in the BLA of observers, which form during a prior similar aversive experience with shock, are reactivated by ventral hippocampal neurons in response to shock delivery to the familiar demonstrator to elicit Exp OF. Finally, we discuss the implications of fear memory engram cells in Exp OF and directions of future research that are of both translational and basic interest.

Hemispherically lateralized rhythmic oscillations in the cingulate-amygdala circuit drive affective empathy in mice.

Observational fear, a form of emotional contagion, is thought to be a basic form of affective empathy. However, the neural process engaged at the specific moment when socially acquired information provokes an emotional response remains elusive. Here, we show that reciprocal projections between the anterior cingulate cortex (ACC) and basolateral amygdala (BLA) in the right hemisphere are essential for observational fear, and 5-7 Hz neural oscillations were selectively increased in those areas at the onset of observational freezing. A closed-loop disruption demonstrated the causal relationship between 5-7 Hz oscillations in the cingulo-amygdala circuit and observational fear responses. The increase/decrease in theta power induced by optogenetic manipulation of the hippocampal theta rhythm bi-directionally modulated observational fear. Together, these results indicate that hippocampus-dependent 5-7 Hz oscillations in the cingulo-amygdala circuit in the right hemisphere are the essential component of the cognitive process that drives empathic fear, but not freezing, in general.

Dorsomedial prefrontal hypoexcitability underlies lost empathy in frontotemporal dementia.

Empathic function is essential for the well-being of social species. Empathy loss is associated with various brain disorders and represents arguably the most distressing feature of frontotemporal dementia (FTD), a leading form of presenile dementia. The neural mechanisms are unknown. We established an FTD mouse model deficient in empathy and observed that aged somatic transgenic mice expressing GGGGCC repeat expansions in C9orf72, a common genetic cause of FTD, exhibited blunted affect sharing and failed to console distressed conspecifics by affiliative contact. Distress-induced consoling behavior activated the dorsomedial prefrontal cortex (dmPFC), which developed profound pyramidal neuron hypoexcitability in aged mutant mice. Optogenetic dmPFC inhibition attenuated affect sharing and other-directed consolation in wild-type mice, whereas chemogenetically enhancing dmPFC excitability rescued empathy deficits in mutant mice, even at advanced ages when substantial cortical atrophy had occurred. These results establish cortical hypoexcitability as a pathophysiological basis of empathy loss in FTD and suggest a therapeutic strategy.

A modified mouse model for observational fear learning and the influence of social hierarchy.

Background: Indirectly experiencing traumatic events either by witnessing or learning of a loved one's suffering is associated with the highest prevalence rates of epidemiological features of PTSD. Social species can develop fear by observing conspecifics in distress. Observational fear learning (OFL) is one of the most widely used paradigms for studying fear contagion in mice. However, the impact of empathic fear behavior and social hierarchy on fear transfer in mice is not well understood. Methods: Fear emotions are best characterized in mice by using complementary tests, rather than only freezing behavior, and simultaneously avoiding behavioral variability in different tests across time. In this study, we modified the OFL model by implementing freezing (FZ), open field (OF), and social interaction (SI) tests in a newly designed experimental facility and applied Z-normalization to assess emotionality changes across different behaviors. Results: The integrated emotionality scores revealed a robustly increased emotionality of observer mice and, more importantly, contributed to distinguishing susceptible individuals. Interestingly, fos-positive neurons were mainly found in the interoceptive network, and mice of a lower social rank showed more empathy-like behaviors. Conclusion: Our findings highlight that combining this experimental model with the Z-scoring method yields robust emotionality measures of individual mice, thus making it easier to screen and differentiate between empathic fear-susceptible mice and resilient mice, and refining the translational applicability of these models.

Observational extinction reduces fear and its retention among adolescents and adults.

Observational fear learning has been notably understudied in fear learning research, especially the potential benefits of observational extinction. Additionally, no studies have investigated observational extinction during adolescence, a key developmental stage for the emergence of anxiety disorders. This study compared observational and direct fear extinction following observational fear acquisition among adolescents and adults. Participants underwent differential observational fear acquisition. Next, participants underwent one of three fear extinctions: (1) observational extinction, (2) direct extinction, (3) no-extinction. Thereafter, participants underwent a US reminder and finally, a direct exposure test. Skin conductance response (SCR), self-reported fear, and risk assessment were measured. Differential observational fear acquisition was demonstrated by both age groups across all measures. During extinction, the observational and direct extinction groups did not differ in differential extinction, however, during the US reminder the observational group exhibited higher SCR compared to the direct group, but not the no-extinction group. Finally, during the direct exposure test, the no-extinction group showed greater differential risk assessment and higher SCR compared to the observational and direct groups. Additionally, adolescents showed poorer discrimination between the CSs compared to adults. Observational extinction successfully reduced fear and its retention amongst youth and adults pointing to the potential benefit of vicarious exposure therapy.

Experience of a hierarchical relationship between a pair of mice specifically influences their affective empathy toward each other.

Prior experience of social hierarchy is known to modulate emotional contagion, a basic form of affective empathy. However, it is not known whether this behavioral effect occurs through changes in an individual's traits due to their experience of social hierarchy or specific social interrelationships between the individuals. Groups of four mice with an established in-group hierarchy were used to address this in conjunction with a tube test. The rank-1 and rank-4 mice were designated as the dominant or subordinate groups, respectively. The two individuals in between were designated as the intermediate groups, which were then used as the observers in observational fear learning (OFL) experiments, an assay for emotional contagion. The intermediate observers showed greater OFL responses to the dominant demonstrator than the subordinate demonstrators recruited from the same home-cage. When the demonstrators were strangers from different cages, the intermediate observers did not distinguish between dominant and subordinate, displaying the same level of OFL. In a reverse setting in which the intermediate group was used as the demonstrator, the subordinate observers showed higher OFL responses than the dominant observers, and this occurred only when the demonstrators were cagemates of the observers. Furthermore, the bigger the rank difference between a pair, the higher the OFL level that the observer displayed. Altogether, these results demonstrate that the hierarchical interrelationship established between a given pair of animals is critical for expressing emotional contagion between them rather than any potential changes in intrinsic traits due to the experience of dominant/subordinate hierarchy. PRACTITIONER POINTS: Subordinate observer or dominant demonstrator resulted in higher affective empathic response in familiar pairs but not unfamiliar pairs. The relative social rank of the observer with respect to the demonstrator had a negative linear correlation with the affective empathic response of the observer in familiar pairs but not unfamiliar pairs. The effect of social rank on affective empathy is attributed to the prior social hierarchical interrelationship between them and is not due to intrinsic attributes of an individual based on one's dominance rank.

Hippocampal-amygdala memory circuits govern experience-dependent observational fear.

The empathic ability to vicariously experience the other's fearful situation, a process called observational fear (OF), is critical to survive in nature and function in society. OF can be facilitated by both prior similar fear experience in the observer and social familiarity with the demonstrator. However, the neural circuit mechanisms of experience-dependent OF (Exp OF) remain unknown. Here, we demonstrate that hippocampal-basolateral amygdala (HPC-BLA) circuits in mice without involving the anterior cingulate cortex, considered a center of OF, mediate Exp OF. Dorsal HPC neurons generate fear memory engram cells in BLA encoding prior similar fear experiences, which are essential for Exp OF. On the other hand, ventral HPC neurons respond to the familiar demonstrator's aversive situation during Exp OF, which reactivates the fear memory engram cells in BLA to elicit Exp OF. Our study provides new insights into the memory engram-dependent perception-action coupling that underlies empathic behaviors like Exp OF.

Observational Fear Learning in Rats: Role of Trait Anxiety and Ultrasonic Vocalization.

Rats can acquire fear by observing conspecifics that express fear in the presence of conditioned fear stimuli. This process is called observational fear learning and is based on the social transmission of the demonstrator rat's emotion and the induction of an empathy-like or anxiety state in the observer. The aim of the present study was to investigate the role of trait anxiety and ultrasonic vocalization in observational fear learning. Two experiments with male Wistar rats were performed. In the first experiment, trait anxiety was assessed in a light-dark box test before the rats were submitted to the observational fear learning procedure. In the second experiment, ultrasonic vocalization was recorded throughout the whole observational fear learning procedure, and 22 kHz and 50 kHz calls were analyzed. The results of our study show that trait anxiety differently affects direct fear learning and observational fear learning. Direct fear learning was more pronounced with higher trait anxiety, while observational fear learning was the best with a medium-level of trait anxiety. There were no indications in the present study that ultrasonic vocalization, especially emission of 22 kHz calls, but also 50 kHz calls, are critical for observational fear learning.

Anxiety Sensitivity Moderates the Association Between Father-Child Relationship Security and Fear Transmission.

Observational fear learning can contribute to the development of fear-related psychopathologies, such as anxiety disorders and post-traumatic stress disorder. Observational fear learning is especially relevant during childhood. Parent-child attachment and anxiety sensitivity modulate fear reactions and fear learning but their impact on observational fear learning has not been investigated. This study investigated how these factors contribute to observational fear learning in children. We examined this question among 55 healthy parent-child dyads. Children (8-12 years old) watched a video of their parent undergoing a direct fear conditioning protocol, where one stimulus (CS+Parent) was paired with a shock and one was not (CS-), and a video of a stranger for whom a different stimulus was reinforced (CS+Stranger). Subsequently, all stimuli were presented to children (without shocks) while skin conductance responses were recorded to evaluate fear levels. Our results showed that children more sensitive to anxiety and who had lower father-child relationship security levels exhibited higher skin conductance responses to the CS+Parent. Our data suggest that the father-child relationship security influences vicarious fear transmission in children who are more sensitive to anxiety. This highlights the importance of the father-child relationship security as a potential modulator of children's vulnerability to fear-related psychopathologies.

Social modulation of fear: Facilitation vs buffering.

Social behaviors largely constitute mutual exchanges of social cues and the responses to them. The adaptive response also requires proper interpretation of the current context. In fear behaviors, social signals have bidirectional effects-some cues elicit or enhance fear whereas other suppress or buffer it. Studies on the social facilitation and social buffering of fear provide evidence of competition between social cues of opposing meanings. Co-expression of opposing cues by the same animal may explain the contradicting outcomes from the interaction between naive and frightened conspecifics, which reflect the fine balance between fear facilitation and buffering. The neuronal mechanisms that determine that balance provide an exciting target for future studies to probe the brain circuits underlying social modulation of emotional behaviors.