Posterior insular cortex is necessary for conditioned inhibition of fear

Naloxone increases conditioned fear responses during social buffering in male rats

Social buffering is the phenomenon in which the presence of an affiliative conspecific mitigates stress responses. We previously demonstrated that social buffering completely ameliorates conditioned fear responses in rats. However, the neuromodulators involved in social buffering are poorly understood. Given that opioids, dopamine, oxytocin and vasopressin play an important role in affiliative behaviour, here, we assessed the effects of the most well-known antagonists, naloxone (opioid receptor antagonist), haloperidol (dopamine D2 receptor antagonist), atosiban (oxytocin receptor antagonist) and SR49059 (vasopressin V1a receptor antagonist), on social buffering. In Experiment 1, fear-conditioned male subjects were intraperitoneally administered one of the four antagonists 25 min prior to exposure to a conditioned stimulus with an unfamiliar non-conditioned rat. Naloxone, but not the other three antagonists, increased freezing and decreased walking and investigation as compared with saline administration. In Experiment 2, identical naloxone administration did not affect locomotor activity, anxiety-like behaviour or freezing in an open-field test. In Experiment 3, after confirming that the same naloxone administration again increased conditioned fear responses, as done in Experiment 1, we measured Fos expression in 16 brain regions. Compared with saline, naloxone increased Fos expression in the paraventricular nucleus of the hypothalamus and decreased Fos expression in the nucleus accumbens shell, anterior cingulate cortex and insular cortex and tended to decrease Fos expression in the nucleus accumbens core. Based on these results, we suggest that naloxone blocks social buffering of conditioned fear responses in male rats.

A fear conditioned cue orchestrates a suite of behaviors in rats

Pavlovian fear conditioning has been extensively used to study the behavioral and neural basis of defensive systems. In a typical procedure, a cue is paired with foot shock, and subsequent cue presentation elicits freezing, a behavior theoretically linked to predator detection. Studies have since shown a fear conditioned cue can elicit locomotion, a behavior that - in addition to jumping, and rearing - is theoretically linked to imminent or occurring predation. A criticism of studies observing fear conditioned cue-elicited locomotion is that responding is non-associative. We gave rats Pavlovian fear discrimination over a baseline of reward seeking. TTL-triggered cameras captured 5 behavior frames/s around cue presentation. Experiment 1 examined the emergence of danger-specific behaviors over fear acquisition. Experiment 2 examined the expression of danger-specific behaviors in fear extinction. In total, we scored 112,000 frames for nine discrete behavior categories. Temporal ethograms show that during acquisition, a fear conditioned cue suppresses reward seeking and elicits freezing, but also elicits locomotion, jumping, and rearing - all of which are maximal when foot shock is imminent. During extinction, a fear conditioned cue most prominently suppresses reward seeking, and elicits locomotion that is timed to shock delivery. The independent expression of these behaviors in both experiments reveals a fear conditioned cue to orchestrate a temporally organized suite of behaviors.

Pharmacological Manipulation of Corticotropin-Releasing Factor Receptors in the Anterior and Posterior Subregions of the Insular Cortex Differently Affects Anxiety-Like Behaviors in the Elevated Plus Maze in Rats

Neuroimaging data in humans and neurobiological studies in rodents have suggested an involvement of the insular cortex (IC) in anxiety manifestations. However, the local neurochemical mechanisms involved are still poorly understood. Corticotropin-releasing factor (CRF) neurotransmission has been described as a prominent neurochemical mechanism involved in the expression of anxiety-like behaviors, but the brain sites related are poorly understood. Additionally, several findings indicate that control of physiological and behavioral responses by the IC occurs in a site-specific manner along its rostrocaudal axis. Thus, this study is aimed at evaluating the effect of CRF receptor agonism and antagonism within the anterior and posterior subregions of the IC in controlling anxiety-related behaviors in the elevated plus maze (EPM). For this, independent groups (six groups) of animals received bilateral microinjections of vehicle, the selective CRF1 receptor antagonist CP376395, or CRF into either the anterior or posterior subregions of the IC. Ten minutes later, the behavior in the EPM was evaluated for five minutes. Treatment of the anterior IC with CP376395, but not with CRF, increased the time and number of entries into the open arms of the EPM. CRF, but not the CRF1 receptor antagonist, microinjected into the posterior IC also increased exploration of the EPM open arms. Taken together, these data indicate that CRFergic neurotransmission in the anterior IC is involved in the expression of anxiety-related behaviors in the EPM. This neurochemical mechanism does not seem to be activated within the posterior IC during exposure to the EPM, but the effects caused by CRF microinjection indicate that activation of CRF receptors in this IC subregion might evoke anxiolytic-like effects.

Psychological and physiological correlates of stimulus discrimination in adults

The discrimination of cues in the environment that signal danger ("fear cue") is important for survival but depends critically on the discernment of such cues from ones that pose no threat ("safety cues"). In rodents, we previously demonstrated the underlying neurobiological mechanisms that support fear versus safety discrimination and documented that these mechanisms extend to the discrimination of reward as well. While learning about reward is equally important for survival, it remains an under-studied area of research, particularly in human studies of conditional discrimination. In the present study, we translated our rodent task of fear reward and neutral discrimination (fear, reward, and neutral discrimination [FRND]) for use in humans. Undergraduate students (N = 53) completed the FRND while electrodermal activity was recorded. Skin conductance response (SCR) amplitude, a marker of arousal response, was derived for fear, reward, and neutral cues that signaled no outcome; critical trials assessed conditional discrimination using combined fear + neutral and reward + neutral cues. Participants provided likeability ratings for each cue type. Results demonstrated that participants rated reward cues the best, fear cues the worst, and neutral cues in between, while SCR amplitude was largest for fear and reward cues and lowest for neutral cues. SCR amplitudes were reduced for fear + neutral (compared to fear) and reward + neutral cues (compared to reward). Results demonstrate that the FRND is a useful paradigm for the assessment of psychological and physiological discrimination of fear and reward. Implications and directions for future work are discussed.

Dissection of insular cortex layer 5 reveals two sublayers with opposing modulatory roles in appetitive drinking behavior

The insular cortex (insula) is known to play a modulatory role in feeding and drinking. Previous studies have revealed anterior-posterior differences of subcortical projections and roles for the insula, yet the anatomical and functional heterogeneity among the cortical layers remains poorly understood. Here, we show that layer 5 of the mouse dysgranular insula has two distinct neuronal subpopulations along the entire anterior-posterior axis: The L5a population, expressing NECAB1, projects bilaterally to the lateral and capsular divisions of the central amygdala, and the L5b population, expressing CTIP2, projects ipsilaterally to the parasubthalamic nucleus and the medial division of the central amygdala. Optogenetically activating L5a and L5b neuronal populations in thirsty male mice led to suppressed and facilitated water spout licking, respectively, without avoidance against or preference for the spout paired with the opto-stimulation. Our results suggest sublayer-specific bidirectional modulatory roles of insula layer 5 in the motivational aspect of appetitive behavior.

Encoding of conditioned inhibitors of fear in the infralimbic cortex

Cues in the environment signaling the absence of threat, i.e. safety, can influence both fear and reward-seeking behaviors. Heightened and maladaptive fear is associated with reduced activity in the medial prefrontal cortex. We have previously shown in male rats that the infralimbic (IL) prefrontal cortex is necessary for suppressing fear during a safety cue. The objective of the present study was to determine if there was safety cue-specific neural activity within the IL using a Pavlovian conditioning paradigm, where a fear cue was paired with shock, a safety cue was paired with no shock, and a reward cue was paired with sucrose. To investigate how safety cues can suppress fear, the fear and safety cues were presented together as a compound fear + safety cue. Single-unit activity showed a large proportion of neurons with excitatory responses to the fear + safety cue specifically, a separate group of neurons with excitatory responses to both the reward and fear + safety cues, and bidirectional neurons with excitation to the fear + safety cue and inhibition to the fear cue. Neural activity was also found to be negatively correlated with freezing during the fear + safety cue. Together, these data implicate the IL in encoding specific aspects of conditioned inhibitors when fear is being actively suppressed.

From safety to frustration: The neural substrates of inhibitory learning in aversive and appetitive conditioning procedures

Inhibitory associative learning counters the effects of excitatory learning, whether appetitively or aversively motivated. Moreover, the affective responses accompanying the inhibitory associations are of opponent valence to the excitatory conditioned responses. Inhibitors for negative aversive outcomes (e.g. shock) signal safety, while inhibitors for appetitive outcomes (e.g. food reward) elicit frustration and/or disappointment. This raises the question as to whether studies using appetitive and aversive conditioning procedures should demonstrate the same neural substrates for inhibitory learning. We review the neural substrates of appetitive and aversive inhibitory learning as measured in different procedural variants and in the context of the underpinning excitatory conditioning on which it depends. The mesocorticolimbic dopamine pathways, retrosplenial cortex and hippocampus are consistently implicated in inhibitory learning. Further neural substrates identified in some procedural variants may be related to the specific motivation of the learning task and modalities of the learning cues. Finally, we consider the translational implications of our understanding of the neural substrates of inhibitory learning, for obesity and addictions as well as for anxiety disorders.

Insular cortical circuits as an executive gateway to decipher threat or extinction memory via distinct subcortical pathways

Threat and extinction memories are crucial for organisms’ survival in changing environments. These memories are believed to be encoded by separate ensembles of neurons in the brain, but their whereabouts remain elusive. Using an auditory fear-conditioning and extinction paradigm in male mice, here we discovered that two distinct projection neuron subpopulations in physical proximity within the insular cortex (IC), targeting the central amygdala (CeA) and nucleus accumbens (NAc), respectively, to encode fear and extinction memories. Reciprocal intracortical inhibition of these two IC subpopulations gates the emergence of either fear or extinction memory. Using rabies-virus-assisted tracing, we found IC-NAc projection neurons to be preferentially innervated by intercortical inputs from the orbitofrontal cortex (OFC), specifically enhancing extinction to override fear memory. These results demonstrate that IC serves as an operation node harboring distinct projection neurons that decipher fear or extinction memory under the top-down executive control from OFC.

Ensembles of fear and extinction memories compete and interact to drive opposing behaviors. Here the authors identified insular cortical circuits as an executive gateway that decipher between fear and extinction memories via distinct subcortical pathways.

Cortico-Striatal Activity Characterizes Human Safety Learning via Pavlovian Conditioned Inhibition

Safety learning generates associative links between neutral stimuli and the absence of threat, promoting the inhibition of fear and security-seeking behaviors. Precisely how safety learning is mediated at the level of underlying brain systems, particularly in humans, remains unclear. Here, we integrated a novel Pavlovian conditioned inhibition task with ultra-high field (7 Tesla) fMRI to examine the neural basis of safety learning in 49 healthy participants. In our task, participants were conditioned to two safety signals: a conditioned inhibitor that predicted threat omission when paired with a known threat signal (A+/AX-), and a standard safety signal that generally predicted threat omission (BC-). Both safety signals evoked equivalent autonomic and subjective learning responses but diverged strongly in terms of underlying brain activation (PFDR whole-brain corrected). The conditioned inhibitor was characterized by more prominent activation of the dorsal striatum, anterior insular, and dorsolateral PFC compared with the standard safety signal, whereas the latter evoked greater activation of the ventromedial PFC, posterior cingulate, and hippocampus, among other regions. Further analyses of the conditioned inhibitor indicated that its initial learning was characterized by consistent engagement of dorsal striatal, midbrain, thalamic, premotor, and prefrontal subregions. These findings suggest that safety learning via conditioned inhibition involves a distributed cortico-striatal circuitry, separable from broader cortical regions involved with processing standard safety signals (e.g., CS-). This cortico-striatal system could represent a novel neural substrate of safety learning, underlying the initial generation of "stimulus-safety" associations, distinct from wider cortical correlates of safety processing, which facilitate the behavioral outcomes of learning.SIGNIFICANCE STATEMENT Identifying safety is critical for maintaining adaptive levels of anxiety, but the neural mechanisms of human safety learning remain unclear. Using 7 Tesla fMRI, we compared learning-related brain activity for a conditioned inhibitor, which actively predicted threat omission, and a standard safety signal (CS-), which was passively unpaired with threat. The inhibitor engaged an extended circuitry primarily featuring the dorsal striatum, along with thalamic, midbrain, and premotor/PFC regions. The CS- exclusively involved cortical safety-related regions observed in basic safety conditioning, such as the vmPFC. These findings extend current models to include learning-specific mechanisms for encoding stimulus-safety associations, which might be distinguished from expression-related cortical mechanisms. These insights may suggest novel avenues for targeting dysfunctional safety learning in psychopathology.

Insular cortex corticotropin-releasing factor integrates stress signaling with social affective behavior

Impairments in identifying and responding to the emotions of others manifest in a variety of psychopathologies. Therefore, elaborating the neurobiological mechanisms that underpin social responses to social emotions, or social affective behavior, is a translationally important goal. The insular cortex is consistently implicated in stress-related social and anxiety disorders, which are associated with diminished ability to make and use inferences about the emotions of others to guide behavior. We investigated how corticotropin-releasing factor (CRF), a neuromodulator evoked upon exposure to stressed conspecifics, influenced the insula. We hypothesized that social affective behavior requires CRF signaling in the insular cortex in order to detect stress in social interactions. In acute slices from male and female rats, CRF depolarized insular pyramidal neurons. In males, but not females, CRF suppressed presynaptic GABAergic inhibition leading to greater excitatory synaptic efficacy in a CRF receptor 1 (CRF1)- and cannabinoid receptor 1 (CB1)-dependent fashion. In males only, insular CRF increased social investigation, and CRF1 and CB1 antagonists interfered with social interactions with stressed conspecifics. To investigate the molecular and cellular basis for the effect of CRF we examined insular CRF1 and CB1 mRNAs and found greater total insula CRF1 mRNA in females but greater CRF1 and CB1 mRNA colocalization in male insular cortex glutamatergic neurons that suggest complex, sex-specific organization of CRF and endocannabinoid systems. Together these results reveal a new mechanism by which stress and affect contribute to social affective behavior.

Role of the anterior insular cortex in restraint-stress induced fear behaviors

Anxiety disorders, such as post-traumatic stress disorder (PTSD), are thought to occur by dysfunction in the fear and anxiety-related brain circuit, however, the exact mechanisms remain unknown. Recent human studies have shown that the right anterior insular cortex (aIC) activity is positively correlated with the severity of PTSD symptoms. Understanding the role of the aIC in fear and anxiety may provide insights into the etiology of anxiety disorders. We used a modified shock-probe defensive burying behavioral test, which utilizes the natural propensity of rodents to bury potentially dangerous objects, to test the role of aIC in fear. Mice exposed to restraint stress exhibited burying of the restrainer-resembling object, indicative of defensive behavior. Electrolytic ablation of the aIC significantly diminished this defensive burying behavior, suggesting the involvement of the aIC. Single-unit recording of pyramidal neurons in the aIC showed that a proportion of neurons which increased activity in the presence of a restrainer-resembling object was significantly correlated with the defensive burying behavior. This correlation was only present in mice exposed to restraint stress. These results suggest that altered neuronal representation in the aIC may regulate fear and anxiety after exposure to a traumatic event. Overall, our result demonstrates that the aIC mediates fear and anxiety and that it could be a potential target for treating anxiety disorders.

Glutamatergic synapses from the insular cortex to the basolateral amygdala encode observational pain

Empathic pain has attracted the interest of a substantial number of researchers studying the social transfer of pain in the sociological, psychological, and neuroscience fields. However, the neural mechanism of empathic pain remains elusive. Here, we establish a long-term observational pain model in mice and find that glutamatergic projection from the insular cortex (IC) to the basolateral amygdala (BLA) is critical for the formation of observational pain. The selective activation or inhibition of the IC-BLA projection pathway strengthens or weakens the intensity of observational pain, respectively. The synaptic molecules are screened, and the upregulated synaptotagmin-2 and RIM3 are identified as key signals in controlling the increased synaptic glutamate transmission from the IC to the BLA. Together, these results reveal the molecular and synaptic mechanisms of a previously unidentified neural pathway that regulates observational pain in mice.

Insular cortex modulates social avoidance of sick rats

Avoidance of sick individuals is vital to the preservation of one's health and preventing transmission of communicable diseases. To do this successfully, one must identify social cues for sickness, which include sickness behaviors and chemosignals, and use this information to orchestrate social interactions. While many social species are highly capable with this process, the neural mechanisms that provide for social responses to sick individuals are only partially understood. To this end, we used a task in which experimental rats were allowed to investigate two conspecifics, one healthy and one sick. To imitate sickness, one conspecific received the viral mimic Polyinosinic:polycytidylic acid (Poly I:C) and the other saline. In a 5-minute social preference test, experimental male and female adult rats avoided Poly I:C treated adult conspecifics but did not adjust social interaction in response to Poly I:C treated juvenile conspecifics. Seeking a neural locus of this behavior, we inhibited the insular cortex, a region necessary for social behaviors directed toward conspecifics in distress. Insular cortex inactivation via administration of the GABAA agonist muscimol to experimental rats prior to social preference tests eliminated the preference to avoid sick adult conspecifics. These results suggest that some aspect of conspecific illness may be encoded in the insular cortex which is anatomically positioned to coordinate a situationally appropriate social response.

Environmental certainty influences the neural systems regulating responses to threat and stress

Flexible calibration of threat responding in accordance with the environment is an adaptive process that allows an animal to avoid harm while also maintaining engagement of other goal-directed actions. This calibration process, referred to as threat response regulation, requires an animal to calculate the probability that a given encounter will result in a threat so they can respond accordingly. Here we review the neural correlates of two highly studied forms of threat response suppression: extinction and safety conditioning. We focus on how relative levels of certainty or uncertainty in the surrounding environment alter the acquisition and application of these processes. We also discuss evidence indicating altered threat response regulation following stress exposure, including enhanced fear conditioning, and disrupted extinction and safety conditioning. To conclude, we discuss research using an animal model of coping that examines the impact of stressor controllability on threat responding, highlighting the potential for previous experiences with control, or other forms of coping, to protect against the effects of future adversity.

Fear balance is maintained by bodily feedback to the insular cortex in mice

[Figure: see text].

The head and the heart of fear

[Figure: see text].

Safety learning and the Pavlovian conditioned inhibition of fear in humans: Current state and future directions

Safety learning occurs when an otherwise neutral stimulus comes to signal the absence of threat, allowing organisms to use safety information to inhibit fear and anxiety in nonthreatening environments. Although it continues to emerge as a topic of relevance in biological and clinical psychology, safety learning remains inconsistently defined and under-researched. Here, we analyse the Pavlovian conditioned inhibition paradigm and its application to the study of safety learning in humans. We discuss existing studies; address outstanding theoretical considerations; and identify prospects for its further application. Though Pavlovian conditioned inhibition presents a theoretically sound model of safety learning, it has been investigated infrequently, with decade-long interims between some studies, and notable methodological variability. Consequently, we argue that the full potential of conditioned inhibition as a model for human safety learning remains untapped, and propose that it could be revisited as a framework for addressing timely questions in the behavioural and clinical sciences.

Imaging of Functional Brain Circuits during Acquisition and Memory Retrieval in an Aversive Feedback Learning Task: Single Photon Emission Computed Tomography of Regional Cerebral Blood Flow in Freely Behaving Rats

Active avoidance learning is a complex form of aversive feedback learning that in humans and other animals is essential for actively coping with unpleasant, aversive, or dangerous situations. Since the functional circuits involved in two-way avoidance (TWA) learning have not yet been entirely identified, the aim of this study was to obtain an overall picture of the brain circuits that are involved in active avoidance learning. In order to obtain a longitudinal assessment of activation patterns in the brain of freely behaving rats during different stages of learning, we applied single-photon emission computed tomography (SPECT). We were able to identify distinct prefrontal cortical, sensory, and limbic circuits that were specifically recruited during the acquisition and retrieval phases of the two-way avoidance learning task.

Pre-adolescent stress disrupts adult, but not adolescent, safety learning

Anxiety disorders are highly prevalent across the lifespan, although diagnoses peak early in adolescence. As a method for inhibiting fear, safety signals have the potential to augment conventional treatments for anxiety. However, the ability to acquire and use safety signals during adolescence remains unclear. Moreover, the impact of stress on safety learning has received surprisingly little attention given that stress is a major factor preceding anxiety onset. In this study, mice were trained in a discriminative conditioning protocol to facilitate safety learning and were tested for fear inhibition using a conditioned safety signal. Next, independent groups of mice were exposed to chronic unpredictable stress (CUS) conditions between postnatal day 22 and 28, followed by tests for anxiety-like phenotypes or fear inhibition using a safety signal, performed either 24 h or five weeks following CUS. Pre-adolescent CUS reduced weight in adolescence and this effect endured into adulthood. CUS also increased specific anxiety-like behaviors in adolescence that were unique from the increase in anxiety observed in adulthood. Despite increased anxiety-like behaviors, adolescents were able to learn about and effectively use safety signals to inhibit fear. In contrast, adults that experienced CUS showed a subtle increase in anxiety but had impaired safety signal learning and usage. Together, these findings indicate that pre-adolescent stress has immediate and enduring effects on anxiety-like behaviors but impairs the capacity for conditioned inhibition only following incubation.

The posterior insular cortex is necessary for the consolidation of tone fear conditioning

The insular cortex (IC) is notably implicated in emotional and cognitive processing; however, little is known regarding to what extent its two main subregions play functionally distinct roles on memory consolidation of conditioned fear tasks. Here we verified the effects of temporary functional inactivation of the anterior (aIC) and posterior IC (pIC) on contextual and tone fear memory. Rats received post-training bilateral infusions of the GABA_A receptor agonist muscimol into either the aIC or pIC and were tested 48 and 72 h after the delay tone fear conditioning session to assess the background contextual (CFC) and tone (TFC) fear conditioning, respectively. Inactivation of the aIC during memory consolidation did not affect fear memory for CFC or TFC. On the other hand, post-training inactivation of the pIC impaired TFC but not CFC. Our findings indicate that the pIC is a necessary part of the neural circuitry related to the consolidation of cued-fear memories.

Infralimbic cortical glutamate output is necessary for the neural and behavioral consequences of chronic stress

Exposure to prolonged stress is a major risk-factor for psychiatric disorders such as generalized anxiety and major depressive disorder. Human imaging studies have identified structural and functional abnormalities in the prefrontal cortex of subjects with depression and anxiety disorders, particularly Brodmann's area 25 (BA25). Further, deep brain stimulation of BA25 reduces symptoms of treatment-resistant depression. The rat homolog of BA25 is the infralimbic cortex (IL), which is critical for cognitive appraisal, executive function, and physiological stress reactivity. Previous studies indicate that the IL undergoes stress-induced changes in excitatory/inhibitory balance culminating in reduced activity of glutamate output neurons. However, the regulatory role of IL glutamate output in mood-related behaviors after chronic variable stress (CVS) is unknown. Here, we utilized a lentiviral-packaged small-interfering RNA to reduce translation of vesicular glutamate transporter 1 (vGluT1 siRNA), thereby constraining IL glutamate output. This viral-mediated gene transfer was used in conjunction with a quantitative anatomical analysis of cells expressing the stable immediate-early gene product FosB/ΔFosB, which accumulates in response to repeated neural activation. Through assessment of FosB/ΔFosB-expressing neurons across the frontal lobe in adult male rats, we mapped regions altered by chronic stress and determined the coordinating role of the IL in frontal cortical plasticity. Specifically, CVS-exposed rats had increased density of FosB/ΔFosB-expressing cells in the IL and decreased density in the insula. The latter effect was dependent on IL glutamate output. Next, we examined the interaction of CVS and reduced IL glutamate output in behavioral assays examining coping, anxiety-like behavior, associative learning, and nociception. IL glutamate knockdown decreased immobility during the forced swim test compared to GFP controls, both in rats exposed to CVS as well as rats without previous stress exposure. Further, vGluT1 siRNA prevented CVS-induced avoidance behaviors, while also reducing risk aversion and passive coping. Ultimately, this study identifies the necessity of IL glutamatergic output for regulating frontal cortical neural activity and behavior following chronic stress. These findings also highlight how disruption of excitatory/inhibitory balance within specific frontal cortical cell populations may impact neurobehavioral adaptation and lead to stress-related disorders.

Juvenile stress facilitates safety learning in male and female high alcohol preferring mice

Adversities during juvenility increase the risk for stress-related disorders, such as post-traumatic stress disorder (PTSD) and alcohol use disorder. However, stress can also induce coping mechanisms beneficial for later stressful experiences. We reported previously that mice selectively bred for high alcohol preference (HAP) exposed to stress during adolescence (but not during adulthood) showed enhanced fear-conditioned responses in adulthood, as measured by fear-potentiated startle (FPS). However, HAP mice also showed enhanced responding to safety cues predicting the absence of foot shocks in adulthood. Here, we pursue these findings in HAP mice by investigating in further detail how juvenile stress impacts the acquisition of safety and fear learning. HAP mice were subjected to three days of juvenile stress (postnatal days 25, 27, 28) and discriminative safety/fear conditioning in adulthood. FPS was used to assess safety versus fear cue discrimination, fear learning, and fear inhibition by the safety cue. Both stressed and unstressed HAP mice were able to discriminate between both cues as well as learn the fear cue-shock association. Interestingly, it was only the previously stressed mice that were able to inhibit their fear response when the fear cue was co-presented with the safety cue, thus demonstrating safety learning. We also report an incidental finding of alopecia in the juvenile stress groups, a phenotype seen in stress-related disorders. These results in HAP mice may be relevant to understanding the influence of juvenile trauma for individual risk and resilience toward developing PTSD and how individuals might benefit from safety cues in behavioral psychotherapy.

Calming Effects of Touch in Human, Animal, and Robotic Interaction-Scientific State-of-the-Art and Technical Advances

Small everyday gestures such as a tap on the shoulder can affect the way humans feel and act. Touch can have a calming effect and alter the way stress is handled, thereby promoting mental and physical health. Due to current technical advances and the growing role of intelligent robots in households and healthcare, recent research also addressed the potential of robotic touch for stress reduction. In addition, touch by non-human agents such as animals or inanimate objects may have a calming effect. This conceptual article will review a selection of the most relevant studies reporting the physiological, hormonal, neural, and subjective effects of touch on stress, arousal, and negative affect. Robotic systems capable of non-social touch will be assessed together with control strategies and sensor technologies. Parallels and differences of human-to-human touch and human-to-non-human touch will be discussed. We propose that, under appropriate conditions, touch can act as (social) signal for safety, even when the interaction partner is an animal or a machine. We will also outline potential directions for future research and clinical relevance. Thereby, this review can provide a foundation for further investigations into the beneficial contribution of touch by different agents to regulate negative affect and arousal in humans.

Emotional responses in monkeys differ depending on the stimulus type, sex, and neonatal amygdala lesion status

The amygdala plays an essential role in evaluating social information, threat detection, and learning fear associations. Yet, most of that knowledge comes from studies in adult humans and animals with a fully developed amygdala. Given the considerable protracted postnatal development of the amygdala, it is important to understand how early damage to this structure may impact the long-term development of behavior. The current study examined behavioral responses toward social, innate, or learned aversive stimuli among neonatal amygdala lesion (Neo-Aibo; males = 3, females = 3) or sham-operated control (Neo-C; males = 3, females = 4) rhesus macaques. Compared with controls, Neo-Aibo animals exhibited less emotional reactivity toward aversive objects, including faster retrieval of food reward, fewer fearful responses, and more manipulation of objects. This lower reactivity was only seen in response to social and innate aversive stimuli, whereas Neo-Aibo animals had similar responses to controls for learned aversive stimuli. The current study also detected sex differences in behavioral response to aversive stimuli, such that, as compared with males, females took longer to retrieve the food reward across all aversive stimuli types, but only expressed more hostility and more coo vocalizations during learned aversive trials. Early amygdala damage impacted the expression of some, but not all, sex differences. For example, neonatal amygdala damage eliminated the sex difference in object manipulation. These findings add important information that broaden our understanding of the role of the amygdala in the expression of sexually dimorphic behaviors, as well as its role in learning fear associations and threat detection. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Neural correlates of safety learning

Accurate discrimination between safe and dangerous stimuli is essential for survival. Prior research has begun to uncover the neural structures that are necessary for learning this discrimination, but exploration of brain regions involved in this learning process has been mostly limited to males. Recent findings show sex differences in discrimination learning, with reduced fear expression to safe cues in females compared to males. Here, we used male and female Sprague Dawley rats to explore neural activation, as measured by Fos expression, in fear and safety learning related brain regions. Neural activation after fear discrimination (Discrimination) was compared between males and females, as well as with fear conditioned (Fear Only) and stimulus presented (Control) conditions. Correlations of discrimination ability and neural activation were also calculated. We uncovered a correlation between central amygdala (CeA) activation and discrimination abilities in males and females. Anterior medial bed nucleus of the stria terminalis (BNST) was the only region where sex differences in Fos counts were observed in the Discrimination condition, and the only region where neural activation significantly differed between Fear Only and Discrimination conditions. Together, these findings indicate the importance of fear expression circuitry in mediating discrimination responses and generate important questions for future investigation.

The Medial Prefrontal Cortex as a Central Hub for Mental Comorbidities Associated with Chronic Pain

Chronic pain patients frequently develop and suffer from mental comorbidities such as depressive mood, impaired cognition, and other significant constraints of daily life, which can only insufficiently be overcome by medication. The emotional and cognitive components of pain are processed by the medial prefrontal cortex, which comprises the anterior cingulate cortex, the prelimbic, and the infralimbic cortex. All three subregions are significantly affected by chronic pain: magnetic resonance imaging has revealed gray matter loss in all these areas in chronic pain conditions. While the anterior cingulate cortex appears hyperactive, prelimbic, and infralimbic regions show reduced activity. The medial prefrontal cortex receives ascending, nociceptive input, but also exerts important top-down control of pain sensation: its projections are the main cortical input of the periaqueductal gray, which is part of the descending inhibitory pain control system at the spinal level. A multitude of neurotransmitter systems contributes to the fine-tuning of the local circuitry, of which cholinergic and GABAergic signaling are particularly emerging as relevant components of affective pain processing within the prefrontal cortex. Accordingly, factors such as distraction, positive mood, and anticipation of pain relief such as placebo can ameliorate pain by affecting mPFC function, making this cortical area a promising target region for medical as well as psychosocial interventions for pain therapy.

Assaying Fear Memory Discrimination and Generalization: Methods and Concepts

Generalization describes the transfer of conditioned responding to stimuli that perceptually differ from the original conditioned stimulus. One arena in which discriminant and generalized responding is of particular relevance is when stimuli signal the potential for harm. Aversive (fear) conditioning is a leading behavioral model for studying associative learning and memory processes related to threatening stimuli. This article describes a step-by-step protocol for studying discrimination and generalization using cued fear conditioning in rodents. Alternate conditioning paradigms, including context generalization, differential generalization, discrimination training, and safety learning, are also described. The protocol contains instructions for constructing a cued fear memory generalization gradient and methods for isolating discrete cued-from-context cued conditioned responses (i.e., "the baseline issue"). The preclinical study of generalization is highly pertinent in the context of fear learning and memory because a lack of fear discrimination (overgeneralization) likely contributes to the etiology of anxiety-related disorders and post-traumatic stress disorder. © 2020 by John Wiley & Sons, Inc. Basic Protocol 1: Tone cued fear generalization gradient Basic Protocol 2: Quantification of freezing Support Protocol: Alternate conditioning paradigms.

Ventral hippocampus interacts with prelimbic cortex during inhibition of threat response via learned safety in both mice and humans

Heightened fear and inefficient safety learning are key features of fear and anxiety disorders. Evidence-based interventions for anxiety disorders, such as cognitive behavioral therapy, primarily rely on mechanisms of fear extinction. However, up to 50% of clinically anxious individuals do not respond to current evidence-based treatment, suggesting a critical need for new interventions based on alternative neurobiological pathways. Using parallel human and rodent conditioned inhibition paradigms alongside brain imaging methodologies, we investigated neural activity patterns in the ventral hippocampus in response to stimuli predictive of threat or safety and compound cues to test inhibition via safety in the presence of threat. Distinct hippocampal responses to threat, safety, and compound cues suggest that the ventral hippocampus is involved in conditioned inhibition in both mice and humans. Moreover, unique response patterns within target-differentiated subpopulations of ventral hippocampal neurons identify a circuit by which fear may be inhibited via safety. Specifically, ventral hippocampal neurons projecting to the prelimbic cortex, but not to the infralimbic cortex or basolateral amygdala, were more active to safety and compound cues than threat cues, and activity correlated with freezing behavior in rodents. A corresponding distinction was observed in humans: hippocampal-dorsal anterior cingulate cortex functional connectivity-but not hippocampal-anterior ventromedial prefrontal cortex or hippocampal-basolateral amygdala connectivity-differentiated between threat, safety, and compound conditions. These findings highlight the potential to enhance treatment for anxiety disorders by targeting an alternative neural mechanism through safety signal learning.

Aversive state processing in the posterior insular cortex

Triggering behavioral adaptation upon the detection of adversity is crucial for survival. The insular cortex has been suggested to process emotions and homeostatic signals, but how the insular cortex detects internal states and mediates behavioral adaptation is poorly understood. By combining data from fiber photometry, optogenetics, awake two-photon calcium imaging and comprehensive whole-brain viral tracings, we here uncover a role for the posterior insula in processing aversive sensory stimuli and emotional and bodily states, as well as in exerting prominent top-down modulation of ongoing behaviors in mice. By employing projection-specific optogenetics, we describe an insula-to-central amygdala pathway to mediate anxiety-related behaviors, while an independent nucleus accumbens-projecting pathway regulates feeding upon changes in bodily state. Together, our data support a model in which the posterior insular cortex can shift behavioral strategies upon the detection of aversive internal states, providing a new entry point to understand how alterations in insula circuitry may contribute to neuropsychiatric conditions.

Cue-dependent safety and fear learning in a discriminative auditory fear conditioning paradigm in the mouse

Discrimination between sensory stimuli associated with safety and threat is crucial for behavioral decisions. Discriminative conditioning paradigms with two acoustic conditioned stimuli (one paired with shock [CS+], the other unpaired with shock [CS−]) have been widely used as an experimental model for fear learning. However, no attention has been paid to the effect of the CS− on safety in the paradigms, because the CS− served as a neutral cue or elevated the freezing level due to fear generalization although less effectively than the CS+. By using a noise and a tone as two acoustic CSs in a discriminative auditory fear conditioning (AFC) paradigm, here we demonstrate that mice learn safety for the CS− while showing fear for the CS+ with opposing emotional behaviors. We found that after learning mice exhibited a significant suppression of context-dependent freezing during the CS−, but not during the CS+, indicating learned safety without fear generalization for the CS−. In contrast, the mice showed an enhanced level of freezing during the CS+ even in a novel spatial context, indicating cued fear for the CS+. Moreover, the CS+ also induced rapid defensive behaviors, whereas the CS− disinhibited normal exploratory behaviors. On the other hand, mice showed no significant suppression of contextual fear during the CS− in a paradigm with a pair of tone CSs at different frequencies, although they clearly discriminated the two tones. These results suggest our AFC paradigm with the noise and tone CSs as a useful experimental model for cue-dependent discriminative learning of safety and threat.

The Role of the Rodent Insula in Anxiety

The human insula has been consistently reported to be overactivated in all anxiety disorders, activation which has been suggested to be proportional to the level of anxiety and shown to decrease with effective anxiolytic treatment. Nonetheless, studies evaluating the direct role of the insula in anxiety are lacking. Here, we set out to investigate the role of the rodent insula in anxiety by either inactivating different insular regions via microinjections of glutamatergic AMPA receptor antagonist CNQX or activating them by microinjection of GABA receptor antagonist bicuculline in rats, before measuring anxiety-like behavior using the elevated plus maze. Inactivation of caudal and medial insular regions induced anxiogenic effects, while their activation induced anxiolytic effects. In contrast, inactivation of more rostral areas induced anxiolytic effects and their activation, anxiogenic effects. These results suggest that the insula in the rat has a role in the modulation of anxiety-like behavior in rats, showing regional differences; rostral regions have an anxiogenic role, while medial and caudal regions have an anxiolytic role, with a transition area around bregma +0.5. The present study suggests that the insula has a direct role in anxiety.

Psychophysiological treatment outcomes: Corticotropin-releasing factor type 1 receptor antagonist increases inhibition of fear-potentiated startle in PTSD patients

After exposure to a traumatic event, a subset of people develop post-traumatic stress disorder (PTSD). One of the key deficits in PTSD is regulation of fear, and impaired inhibition of fear-potentiated startle (FPS) has been identified as a potential physiological biomarker specific to PTSD. As part of a larger clinical trial, this study investigated the effects of a CRF receptor 1 antagonist, GSK561679, on inhibition of fear-potentiated startle during a conditional discrimination fear-conditioning paradigm, termed AX+/BX-. Prior research using this paradigm has demonstrated deficits in inhibition of conditioned fear in several PTSD populations. The randomized, double-blind, placebo-controlled clinical trial compared fear inhibition between female PTSD participants taking 350 mg/day GSK561679 (n = 47 pre- and 29 post-treatment) and patients taking a placebo pill (n = 52 pre- and 30 post-treatment) daily for 6 weeks. There was no significant difference between the two groups in their acquisition of fear or discrimination between threat and safety cues, and no pre-post-treatment effect on these measures. However, there was a significant effect of treatment on inhibition of FPS during the AB trials in the AX+/BX- transfer test (p < 0.05). While all PTSD participants showed typical impairments in fear inhibition prior to treatment, GSK561679 enhanced fear inhibition post-treatment, independent of clinical effects. The current study suggests that CRF receptor 1 antagonism may have specific effects within neural circuitry mediating fear inhibition responses, but not overall symptom presentation, in PTSD.

Basolateral amygdala inactivation eliminates fear-induced underestimation of time in a temporal bisection task

We examined interval timing - time perception in the seconds-to-minutes range - of the fear-inducing stimulus and the role of the amygdala in this phenomenon. Rats were initially trained to perform a temporal bisection task, in which their responses to levers A and B were reinforced following 2-s and 8-s tones, respectively. After acquisition, the rats were also presented with tones of intermediate durations and pressed one of the two levers to indicate whether the tone duration was closer to 2 or 8 s. Subsequently, the rats underwent differential fear conditioning, in which one frequency tone (conditioned stimulus; CS+) was paired with an electric foot shock, whereas another frequency tone (CS-) was presented alone. The rats were then infused with artificial cerebrospinal fluid (aCSF) or the GABA_A agonist muscimol into the bilateral basolateral amygdala (BLA) before performing the bisection task with CS+ and CS-. In rats infused with aCSF, the psychophysical function shifted rightward in CS+ relative to that in CS-. Moreover, the point of subjective equality of the CS+ was higher than that of CS-, suggesting that the duration of the fear -CS was perceived as shorter than that of the neutral CS. However, muscimol infusion into the BLA abolished this difference, suggesting that BLA inactivation suppresses the effect of the fear -CS. Our results demonstrate that normal BLA activity is essential for fear-induced underestimation of time.

Insular cortex inactivation generalizes fear-induced underestimation of interval timing in a temporal bisection task

In this study, we investigated: (1) the effect of fear on interval timing-time perception in the seconds-to-minutes range-and (2) the role of the insular cortex in the modulation of this effect. Rats were first trained on a temporal bisection task in which their response to a lever A was reinforced following a 2.00-s tone, whereas their response to a lever B was reinforced following an 8.00-s tone. After acquisition, the rats were also presented with intermediate-duration tones and pressed one of two levers to indicate whether tone duration was closer to 2.00 or 8.00s. Subsequently, the rats underwent differential fear conditioning in which one pitch tone (conditioned stimulus; CS+) was paired with an electric foot shock, while the other pitch tone (CS-) was presented alone. Either artificial cerebrospinal fluid (aCSF) or the GABA_A agonist muscimol was then infused into the rats' bilateral insular cortex before the animals were tested on the bisection task using the CS+and CS- tones. We found that in the rats infused with aCSF, the point of subjective equality (PSE) of the CS+ was higher than that for CS-, suggesting that the duration for CS+ was perceived to be shorter than that of CS-. However, muscimol eliminated the difference in PSE between CS+ and CS- by generalizing of the effect from CS+to the CS-. Taken together, our results show that normal activity in the insular cortex is involved in fear-induced modulation of interval timing.

Cued fear memory generalization increases over time

Fear memory is a highly stable and durable form of memory, even over vast (remote) time frames. Nevertheless, some elements of fear memory can be forgotten, resulting in generalization. The purpose of this study is to determine how cued fear memory generalizes over time and measure underlying patterns of cortico-amygdala synaptic plasticity. We established generalization gradients at recent (1-d) and remote (30-d) retention intervals following auditory cued fear conditioning in adult male C57BL/6 mice. Results revealed a flattening of the generalization gradient (increased generalization) that was dissociated from contextual fear generalization, indicating a specific influence of time on cued fear memory performance. This effect reversed after a brief exposure to the novel stimulus soon after learning. Measurements from cortico-amygdala imaging of the activity-regulated cytoskeletal Arc/arg 3.1 (Arc) protein using immunohistochemistry after cued fear memory retrieval revealed a stable pattern of Arc expression in the dorsolateral amygdala, but temporally dynamic expression in the cortex. Over time, increased fear memory generalization was associated with a reduction in Arc expression in the agranular insular and infralimbic cortices while discrimination learning was associated with increased Arc expression in the prelimbic cortex. These data identify the dorsolateral amygdala, medial prefrontal, and insular cortices as loci for synaptic plasticity underlying cued fear memory generalization over time.

Inactivation of the Ventrolateral Orbitofrontal Cortex Impairs Flexible Use of Safety Signals

Survival depends on adaptation to shifting environmental risks and opportunities. Regarding risks, the mechanisms which permit acquisition, recall, and flexible use of aversive associations is poorly understood. Drawing on the evidence that the orbital frontal cortex is critical to integrating outcome expectancies with flexible appetitive behavioral responses, we hypothesized that OFC would contribute to behavioral flexibility within an aversive learning domain. We introduce a fear conditioning procedure in which adult male rats were presented with shock-paired conditioned stimulus (CS+) or a safety cue (CS-). In a recall test, rats exhibit greater freezing to the CS+ than the CS-. Temporary inactivation of the ventrolateral OFC with muscimol prior to conditioning did not affect later discrimination, but inactivation after learning and prior to recall impaired discrimination between safety and danger cues. This result complements prior research in the appetitive domain and suggests that the OFC plays a general role in behavioral flexibility regardless of the valence of the CS.

Sex differences in fear discrimination do not manifest as differences in conditioned inhibition

Distinguishing safety from danger is necessary for survival, but is aberrant in individuals with post-traumatic stress disorder (PTSD). While PTSD is more prevalent in women than men, research on sex differences in safety learning is limited. Here, female rats demonstrated greater fear discrimination than males in a CS+/CS− paradigm. To determine if this sex difference transferred to fear inhibition, rats were tested for conditioned inhibition in a summation test with the CS+ and CS− presented in compound; no sex difference emerged. The results suggest sex differences in the neural mechanisms of discrimination learning but not recall of a fear inhibitor.