Emotional perseveration: an update on prefrontal-amygdala interactions in fear extinction

Chemogenetic inactivation of the nucleus reuniens and its projections to the orbital cortex produce deficits on discrete measures of behavioral flexibility in the attentional set-shifting task

The nucleus reuniens (RE) of the ventral midline thalamus is a critical node in the communication between the orbitomedial prefrontal cortex (OFC) and the hippocampus (HF). While RE has been shown to directly participate in memory-associated functions through its connections with the medial prefrontal cortex and HF, less is known regarding the role of RE in executive functioning. Here, we examined the involvement of RE and its projections to the orbital cortex (ORB) in attention and behavioral flexibility in male rats using the attentional set shifting task (AST). Rats expressing the hM4Di DREADD receptor in RE were implanted with indwelling cannulas in either RE or the ventromedial ORB to pharmacologically inhibit RE or its projections to the ORB with intracranial infusions of clozapine-N-oxide hydrochloride (CNO). Chemogenetic-induced suppression of RE resulted in impairments in reversal learning and set-shifting. This supports a vital role for RE in behavioral flexibility - or the ability to adapt behavior to changing reward or rule contingencies. Interestingly, CNO suppression of RE projections to the ventromedial ORB produced impairments in rule abstraction - or dissociable effects elicited with direct RE suppression. In summary, the present findings indicate that RE, mediated in part by actions on the ORB, serves a critical role in the flexible use of rules to drive goal directed behavior. The cognitive deficits of various neurological disorders with impaired communication between the HF and OFC, may be partly attributed to alterations of RE -- as an established intermediary between these cortical structures.

Involvement of dysregulated hippocampal histone H3K9 methylation at the promoter of the BDNF gene in impaired memory extinction

RATIONALE

Since the precise mechanisms of posttraumatic stress disorder (PTSD) remain unknown, effective treatment interventions have not yet been established. Impaired extinction of fear memory (EFM) is one of the core symptoms of PTSD and is associated with stress-induced epigenetic change in gene expression.

OBJECTIVES

In this study, we examined whether the involvement of histone H3 lysine 9 dimethylation (H3K9me2) in EFM is mediated through brain-derived neurotrophic factor (BDNF) expression in the hippocampus, and whether BIX01294, a selective G9a and GLP histone methyltransferase inhibitor, could be treatment for impaired EFM in an animal model of PTSD.

METHODS

The single prolonged stress (SPS) paradigm was used to model PTSD. We measured BDNF mRNA levels by RT-PCR, and H3K9me2 levels in the BDNF gene promoters by chromatin immunoprecipitation-qPCR. After undergoing contextual fear conditioning and hippocampal injection of BIX01294, male rats were subjected to extinction training and extinction testing and their freezing times and BDNF mRNA levels were measured.

RESULTS

Compared to sham rats, SPS rats showed decreased BDNF mRNA levels 2 h after extinction training, no significant changes in levels of global H3K9me2 prior to extinction training, and increased levels of H3K9me2 in BDNF gene promoter IV, but not in BDNF gene promoter I. Administration of BIX01294 ameliorated the decrease in BDNF mRNA levels 2 h after extinction training and subsequently alleviated impaired EFM in extinction tests in SPS rats.

CONCLUSION

We conclude that reduced hippocampal levels of BDNF mRNA due to increase in H3K9me2 levels may play a role in PTSD-associated EFM impairment, and BIX01294 could be a PTSD treatment option.

Role of the prefrontal cortical protease TACE/ADAM17 in neurobehavioral responses to chronic stress during adolescence

INTRODUCTION

Chronic adolescent stress profoundly affects prefrontal cortical networks regulating top-down behavior control. However, the neurobiological pathways contributing to stress-induced alterations in the brain and behavior remain largely unknown. Chronic stress influences brain growth factors and immune responses, which may, in turn, disrupt the maturation and function of prefrontal cortical networks. The tumor necrosis factor alpha-converting enzyme/a disintegrin and metalloproteinase 17 (TACE/ADAM17) is a sheddase with essential functions in brain maturation, behavior, and inflammatory responses. This study aimed to determine the impact of stress on the prefrontal cortex and whether TACE/ADAM17 plays a role in these responses.

METHODS

We used a Lewis rat model that incorporates critical elements of chronic psychosocial stress, such as uncontrollability, unpredictability, lack of social support, and re-experiencing of trauma.

RESULTS

Chronic stress during adolescence reduced the acoustic startle reflex and social interactions while increasing extracellular free water content and TACE/ADAM17 mRNA levels in the medial prefrontal cortex. Chronic stress altered various ethological behavioral domains in the observation home cages (decreased ingestive behaviors and increased walking, grooming, and rearing behaviors). A group of rats was injected intracerebrally either with a novel Accell™ SMARTpool TACE/ADAM17 siRNA or a corresponding siRNA vehicle (control). The RNAscope Multiplex Fluorescent v2 Assay was used to visualize mRNA expression. Automated puncta quantification and analyses demonstrated that TACE/ADAM17 siRNA administration reduced TACE/ADAM17 mRNA levels in the medial prefrontal cortex (59% reduction relative to control). We found that the rats that received prefrontal cortical TACE/ADAM17 siRNA administration exhibited altered eating patterns (e.g., increased food intake and time in the feeding zone during the light cycle).

CONCLUSION

This study supports that the prefrontal cortex is sensitive to adolescent chronic stress and suggests that TACE/ADAM17 may be involved in the brain responses to stress.

The Associations Between Sleep and Externalizing and Internalizing Problems in Children and Adolescents with Attention-Deficit/Hyperactivity Disorder: Empirical Findings, Clinical Implications, and Future Research Directions

Sleep problems are common in youth with attention-deficit/hyperactivity disorder (ADHD). Externalizing and internalizing problems contribute to dysfunction in youth with ADHD and are amplified by disrupted sleep. This objective of this article is to synthesize empirical studies that examined the associations between sleep and internalizing or externalizing problems in individuals with ADHD. The main findings are that sleep problems precede, predict, and significantly contribute to the manifestation of internalizing and externalizing behavior problems among children and adolescents with ADHD. Clinicians should assess sleep and integrate sleep interventions into the management of youth with ADHD.

Synaptic and transcriptomic features of cortical and amygdala pyramidal neurons predict inefficient fear extinction

Fear-related disorders arise from inefficient fear extinction and have immeasurable social and economic costs. Here, we characterize mouse phenotypes that spontaneously show fear-independent behavioral traits predicting adaptive or maladaptive fear extinction. We find that, already before fear conditioning, specific morphological, electrophysiological, and transcriptomic patterns of cortical and amygdala pyramidal neurons predispose to fear-related disorders. Finally, by using an optogenetic approach, we show the possibility to rescue inefficient fear extinction by activating infralimbic pyramidal neurons and to impair fear extinction by activating prelimbic pyramidal neurons.

MicroRNA expression profiles of stress susceptibility and resilience in the prelimbic and infralimbic cortex of rats after single prolonged stress

The experience of traumatic stress can engender lasting memories associated with the trauma, often resulting in post-traumatic stress disorder (PTSD). However, only a minority of individuals develop PTSD symptoms upon exposure. The neurobiological mechanisms underlying the pathology of PTSD are poorly understood. Utilizing a rat model of PTSD, the Single Prolonged Stress (SPS) paradigm, we were able to differentiate between resilient and susceptible individuals. Fourteen days after the SPS exposure, we conducted the behavioral analyses using Elevated Plus Maze (EPM) and Open Field (OF) tests to identify male rats as trauma resilient or susceptible. We focused on the microRNA (miRNA) profiles of the infralimbic (IL) and prelimbic (PL) cortical regions, known to be crucial in regulating the stress response. Our investigation of stressed rats exposed to the SPS procedure yielded divergent response, and differential expression microRNAs (DEmiRs) analysis indicated significant differences in the IL and PL transcriptional response. In the IL cortex, the GO analysis revealed enriched GO terms in the resilient versus control comparison, specifically related to mitogen-activated protein kinase and MAP kinase signaling pathways for their molecular functions as well as cytosol and nucleoplasm for the biological process. In the susceptible versus resilient comparison, the changes in molecular functions were only manifested in the functions of regulation of transcription involved in the G1/S transition of the mitotic cell cycle and skeletal muscle satellite cell activation. However, no enriched GO terms were found in the susceptible versus control comparison. In the PL cortex, results indicated that the DEmiRs were enriched exclusively in the cellular component level of the endoplasmic reticulum lumen in the comparison between resilient and control rats. Overall, our study utilized an animal model of PTSD to investigate the potential correlation between stress-induced behavioral dysfunction and variations in miRNA expression. The aforementioned discoveries have the potential to pave the way for novel therapeutic approaches for PTSD, which could involve the targeted regulation of transcriptome expression.

Subcortical volume analysis in non-suicidal self-injury adolescents: A pilot study

Given the high prevalence of non-suicidal self-injury (NSSI) among teenagers worldwide, the underlying mechanisms promoting such behavior must be urgently investigated. This study aimed to investigate neurobiological changes in the regional brain in adolescents with NSSI by comparing the volumes of the subcortical structures of 23 female adolescents with NSSI and 23 healthy controls with no history of psychiatric diagnosis or treatment. The NSSI group comprised those who underwent inpatient treatment for non-suicidal self-harm behavior at the Department of Psychiatry at Daegu Catholic University Hospital from July 1, 2018, to December 31, 2018. The control group comprised healthy adolescents from the community. We compared differences in the volume of the bilateral thalamus, caudate, putamen, hippocampus, and amygdala. All statistical analyses were conducted using SPSS Statistics Version 25. The NSSI group exhibited decreased subcortical volume in the left amygdala and marginally decreased subcortical volume in the left thalamus. Our results provide important clues about adolescent NSSI's underlying biology. Analysis of subcortical volumes between the NSSI and normal groups revealed subcortical volume differences in the left amygdala and thalamus, part of the core cerebral regions responsible for emotional processing and regulation, which may help explain the neurobiological mechanism of NSSI.

Facilitated extinction but impaired extinction recall by eye movement manipulation in humans - Indications for action mechanisms and the applicability of eye movement desensitization

Eye movement desensitization and reprocessing (EMDR) therapy utilizes the manipulation of eye movements to reduce affective distress during fear-exposure. Animal research recently suggested a potential neural mechanism underlying these effects, by which increased activity of the superior colliculus (SC), mediating visual attention, increases the inhibition of the basolateral amygdala (BLA), mediating defensive plasticity. We tested such mechanism in forty healthy humans using a multiple-day single-cue fear conditioning and extinction paradigm. The activity of the SC during extinction was experimentally manipulated by eye movements, as half of the participants executed saccadic eye movements (n = 20; major SC involvement), while the other half executed smooth eye pursuits (n = 20; minor SC involvement). Amygdala-mediated fear-potentiated startle responses and fear bradycardia, as well as threat expectancy was analyzed. Saccadic eye movements facilitated the extinction of fear bradycardia and fear-potentiated startle responses. Higher saccadic accuracy and range correlated with reduced fear-potentiated startle. However, during extinction recall, fear-potentiated startle and fear bradycardia resurged and partly reached levels obtained after fear acquisition. Threat expectancy was not affected by different eye movements and was not elevated during extinction recall. Within limitations, results support an inhibitory SC-BLA pathway in humans by which eye movements may reduce low-level defensive responding, but not threat expectancy. Yet, manipulating eye movements during extinction learning seems to impair extinction recall for behavioral and physiological defensive response indices. Thus, increasing SC activity might enhance initial efficacy of exposure treatment, but additional strategies seem necessary for sustained fear attenuation.

Relationships between serotonin availability and frontolimbic response to fearful and threatening faces

Serotonin is a critical neurotransmitter in the regulation of emotional behavior. Although emotion processing is known to engage a corticolimbic circuit, including the amygdala and prefrontal cortex, exactly how this brain system is modulated by serotonin remains unclear. Here, we hypothesized that serotonin modulates variability in excitability and functional connectivity within this circuit. We tested whether this modulation contributes to inter-individual differences in emotion processing. Using a multimodal neuroimaging approach with a simultaneous PET-3T fMRI scanner, we simultaneously acquired BOLD signal while participants viewed emotional faces depicting fear and anger, while also measuring serotonin transporter (SERT) levels, regulating serotonin functions. Individuals with higher activity of the medial amygdala BOLD in response to fearful or angry facial expressions, who were temperamentally more anxious, also exhibited lower SERT availability in the dorsal raphe nucleus (DRN). Moreover, higher connectivity of the medial amygdala with the left dorsolateral prefrontal and the anterior cingulate cortex was associated with lower levels of SERT availability in the DRN. These results demonstrate the association between the serotonin transporter level and emotion processing through changes in functional interactions between the amygdala and the prefrontal areas in healthy humans.

Functional contextual implementation of an evolutionary, entropy-based, and embodied free energy framework: Utilizing Lagrangian mechanics and evolutionary game theory's truth vs. fitness test of the veridicality of phenomenological experience

The Bayesian approach of cognitive science largely takes the position that evolution drives perception to produce precepts that are veridical. However, some efforts utilizing evolutionary game theory simulations have shown that perception is more likely based on a fitness function, which promotes survival rather than promoting perceptual truth about the environment. Although these findings do not correspond well with the standard Bayesian approach to cognition, they may correspond with a behavioral functional contextual approach that is ontologically neutral (a-ontological). This approach, formalized through a post-Skinnerian account of behaviorism called relational frame theory (RFT), can, in fact, be shown to correspond well with an evolutionary fitness function, whereby contextual functions form that corresponds to a fitness function interface of the world. This fitness interface approach therefore may help provide a mathematical description for a functional contextual interface of phenomenological experience. Furthermore, this more broadly fits with a neurological active inference approach based on the free-energy principle (FEP) and more broadly with Lagrangian mechanics. These assumptions of how fitness beats truth (FBT) and FEP correspond to RFT are then discussed within a broader multidimensional and evolutionary framework called the extended evolutionary meta-model (EEMM) that has emerged out of the functional contextual behavioral science literature to incorporate principles of cognition, neurobiology, behaviorism, and evolution and are discussed in the context of a novel RFT framework called "Neurobiological and Natural Selection Relational Frame Theory" (N-frame). This framework mathematically connects RFT to FBT, FEP, and EEMM within a single framework that expands into dynamic graph networking. This is then discussed for its implications of empirical work at the non-ergodic process-based idiographic level as applied to individual and societal level dynamic modeling and clinical work. This discussion is framed within the context of individuals that are described as evolutionary adaptive and conscious (observer-self) agents that minimize entropy and can promote a prosocial society through group-level values and psychological flexibility.

The association between stress, emotional states, and tinnitus: a mini-review

Extensive literature supporting the view of tinnitus induced stress in patients is available. However, limited evidence has been produced studying the opposite, that is, does stress cause tinnitus? The hypothalamus pituitary adrenal axis, one of the main neuroendocrine systems involved in stress response, is commonly disturbed in tinnitus patients. Patients with chronic tinnitus have been shown to develop abnormal responses to psycho-social stress, where the hypothalamus pituitary adrenal axis response is weaker and delayed, suggesting chronic stress contributes to the development of chronic tinnitus. The sympathetic branch of the autonomic nervous system also plays a major role in stress response and its chronic hyperactivity seems to be involved in developing tinnitus. Psycho-social stress has been shown to share the same probability of developing tinnitus as occupational noise and contributes to worsening tinnitus. Additionally, exposure to high stress levels and occupational noise doubles the likelihood of developing tinnitus. Interestingly, short-term stress has been shown to protect the cochlea in animals, but chronic stress exposure has negative consequences. Emotional stress also worsens pre-existing tinnitus and is identified as an important indicator of tinnitus severity. Although there is limited body of literature, stress does seem to play a vital role in the development of tinnitus. This review aims to highlight the association between stress, emotional states, and the development of tinnitus while also addressing the neural and hormonal pathways involved.

Sleep as a protective factor of children's executive functions: A study during COVID-19 confinement

Confinements due to the COVID-19 outbreak affected sleep and mental health of adults, adolescents and children. Already preschool children experienced acutely worsened sleep, yet the possible resulting effects on executive functions remain unexplored. Longitudinally, sleep quality predicts later behavioral-cognitive outcomes. Accordingly, we propose children's sleep behavior as essential for healthy cognitive development. By using the COVID-19 confinement as an observational-experimental intervention, we tested whether worsened children's sleep affects executive functions outcomes 6 months downstream. We hypothesized that acutely increased night awakenings and sleep latency relate to reduced later executive functions. With an online survey during the acute confinement phase we analyzed sleep behavior in 45 children (36-72 months). A first survey referred to the (retrospective) time before and (acute) situation during confinement, and a follow-up survey assessed executive functions 6 months later (6 months retrospectively). Indeed, acutely increased nighttime awakenings related to reduced inhibition at FOLLOW-UP. Associations were specific to the confinement-induced sleep-change and not the sleep behavior before confinement. These findings highlight that specifically acute changes of children's nighttime sleep during sensitive periods are associated with behavioral outcome consequences. This aligns with observations in animals that inducing poor sleep during developmental periods affects later brain function.

Trauma and Remembering: From Neuronal Circuits to Molecules

Individuals with posttraumatic stress disorder (PTSD) experience intrusions of vivid traumatic memories, heightened arousal, and display avoidance behavior. Disorders in identity, emotion regulation, and interpersonal relationships are also common. The cornerstone of PTSD is altered learning, memory, and remembering, regulated by a complex neuronal and molecular network. We propose that the essential feature of successful treatment is the modification of engrams in their unstable state during retrieval. During psychedelic psychotherapy, engrams may show a pronounced instability, which enhances modification. In this narrative review, we outline the clinical characteristics of PTSD, its multifaceted neuroanatomy, and the molecular pathways that regulate memory destabilization and reconsolidation. We propose that psychedelics, acting by serotonin-glutamate interactions, destabilize trauma-related engrams and open the door to change them during psychotherapy.

Is PTSD an Evolutionary Survival Adaptation Initiated by Unrestrained Cytokine Signaling and Maintained by Epigenetic Change?

INTRODUCTION

Treatment outcomes for PTSD with current psychological therapies are poor, with very few patients achieving sustained symptom remission. A number of authors have identified physiological and immune disturbances in Post Traumatic Stress Disorder (PTSD) patients, but there is no unifying hypothesis that explains the myriad features of the disorder.

MATERIALS AND METHODS

The medical literature was reviewed over a 6-year period primarily using the medical database PUBMED.

RESULTS

The literature contains numerous papers that have identified a range of physiological and immune dysfunction in association with PTSD. This paper proposes that unrestrained cytokine signaling induces epigenetic changes that promote an evolutionary survival adaptation, which maintains a defensive PTSD phenotype. The brain can associate immune signaling with past threat and initiate a defensive behavioral response. The sympathetic nervous system is pro-inflammatory, while the parasympathetic nervous system is anti-inflammatory. Prolonged cholinergic withdrawal will promote a chronic inflammatory state. The innate immune cytokine IL-1β has pleiotropic properties and can regulate autonomic, glucocorticoid, and glutamate receptor functions, sleep, memory, and epigenetic enzymes. Changes in epigenetic enzyme activity can potentially alter phenotype and induce an adaptation. Levels of IL-1β correlate with severity and duration of PTSD and PTSD can be prevented by bolus administration of hydrocortisone in acute sepsis, consistent with unrestrained inflammation being a risk factor for PTSD. The nervous and immune systems engage in crosstalk, governed by common receptors. The benefits of currently used psychiatric medication may arise from immune, as well as synaptic, modulation. The psychedelic drugs (3,4-Methylenedioxymethamphetamine (MDMA), psilocybin, and ketamine) have potent immunosuppressive and anti-inflammatory effects on the adaptive immune system, which may contribute to their reported benefit in PTSD. There may be distinct PTSD phenotypes induced by innate and adaptive cytokine signaling.

CONCLUSION

In order for an organism to survive, it must adapt to its environment. Cytokines signal danger to the brain and can induce epigenetic changes that result in a persistent defensive phenotype. PTSD may be the price individuals pay for the genomic flexibility that promotes adaptation and survival.

The independent effects of sleep deprivation and sleep fragmentation on processing of emotional information

Disrupted sleep through sleep deprivation or sleep fragmentation has previously been shown to impair cognitive processing. Nevertheless, limited studies have examined the impact of disrupted sleep on the processing of emotional information. The current study aimed to use an experimental approach to generate sleep disruption and examine whether SD and SF in otherwise healthy individuals would impair emotional facial processing. Thirty-five healthy individuals participated in three-day/two-night laboratory study which consisted of two consecutive overnight polysomnograms and cognitive testing during the day. The first night was an adaptation night of normal sleep while the second was an experimental night where participants underwent either a night of 1) normal sleep, 2) no sleep (SD) or 3) fragmented sleep (SF). The emotional Go/No-Go task was completed in the morning following each night. Data from 33 participants (14 females, mean age = 24.6 years) were included in the final analysis. Following a night of SD or SF, participants performed significantly poorer with emotional (fearful and happy) targets, while no significant changes occurred after a night of normal sleep. Further, sleep deprived individuals experienced additional impairments with notably poorer performance with neutral targets and slower reaction time for all targets, suggesting an overall slowing of cognitive processing speed. These findings suggest that facial recognition in socio-emotional contexts may be impaired in individuals who experience disrupted sleep.

Response to unexpected social inclusion: A study using the cyberball paradigm

BACKGROUND

Dysfunctional expectations are considered core characteristics of Major Depressive Disorder (MDD) and should be focused in psychotherapy. Dysfunctional expectations are especially pronounced in the interpersonal area (social expectations). In the present study, we examine the effect of unexpected social inclusion (expectation violation) on the change of generalized and specific depression-typical social expectations.

METHOD

We conducted an online study to investigate the impact of social inclusion after a period of social exclusion (unexpected social inclusion) on social expectation change (sample size 144) in a non-clinical sample. Depressive symptoms were assessed via self-reporting. Participants took part in two rounds of the online ball-game Cyberball. In the first round, all participants were socially excluded by their two co-players (acquisition of negative social expectations). In the second round, participants were either once more excluded (expectation confirmation) or included equally (expectation violation) by the same co-players. Specific and generalized social expectations were assessed after each round.

RESULTS

Specific and generalized social expectations increased following expectation violation. Even though depressive symptoms were related to lower levels of social expectations, we found that depressive symptoms did not moderate expectation change after positive expectation violations.

CONCLUSIONS

In the present experimental setup including the use of the online ball-game Cyberball, the establishment and change of social expectations can be experimentally manipulated. Under the given circumstances and in a non-clinical sample, negative expectations can be updated after unexpected positive experiences regardless of the number of depressive symptoms. The results are discussed in the context of current models of Major Depressive Disorder (MDD), expectation change, and cognitive behavioral therapy.

Synaptic correlates of associative fear memory in the lateral amygdala

Successful adaptation to the environment requires an accurate response to external threats by recalling specific memories. Memory formation and recall require engram cell activity and synaptic strengthening among activated neuronal ensembles. However, elucidation of the underlying neural substrates of associative fear memory has remained limited without a direct interrogation of extinction-induced changes of specific synapses that encode a specific auditory fear memory. Using dual-eGRASP (enhanced green fluorescent protein reconstitution across synaptic partners), we found that synapses among activated neuronal ensembles or activated synaptic ensembles showed a significantly larger spine morphology at auditory cortex (AC)-to-lateral amygdala (LA) projections after auditory fear conditioning in mice. Fear extinction reversed these enhanced synaptic ensemble spines, whereas re-conditioning with the same tone and shock restored the spine size of the synaptic ensemble. We suggest that synaptic ensembles encode and represent different fear memory states.

Anomalous static and dynamic functional connectivity of amygdala subregions in individuals with high trait anxiety

BACKGROUND

Trait anxiety is considered a susceptible factor for stress-related disorders, and is characterized by abnormal brain activity and connectivity in the regions related to emotional processing (e.g., the amygdala). However, only a few studies have examined the static and dynamic changes of functional connectivity in trait anxiety.

METHOD

We compared the resting-state static and dynamic functional connectivity (sFC/dFC) in individuals with high trait anxiety (HTA, n = 257) and low trait anxiety (LTA, n = 264) using bilateral amygdala subregions as the seeds, that is, the centromedial amygdala (CMA), basolateral amygdala (BLA), and superficial amygdala (SFA).

RESULTS

The CMA, BLA, and SFA all showed reduced sFC with the executive control network (ECN) and anomalous dFC with the default mode network (DMN) in individuals with HTA. The CMA only showed reduced sFC with the ECN and reduced dFC with the DMN in individuals with HTA. The BLA showed reduced sFC with the salience network (mainly in the anterior and median cingulate), and increased dFC between the BLA and the DMN in individuals with HTA compared to those with LTA. Notably, HTA showed widespread anomalous functional connectivity in the SFA, including the visual network, mainly in the calcarine fissure, limbic system (olfactory cortex), and basal ganglia (putamen).

CONCLUSION

The anomalous sFC and dFC in individuals with HTA may reflect altered mechanisms in prefrontal control, salient stimuli processing, and amygdaloidal responsivity to potential threats, leading to alterations in associative, attentional, interpretative, and regulating processes that sustain a threat-related processing bias in HTA individuals.

Chemogenetic activation of the mPFC alleviates impaired fear memory extinction in an animal model of PTSD

BACKGROUND AND AIM

Although impaired extinction of fear memory (EFM) is a hallmark symptom of posttraumatic stress disorder (PTSD), the mechanisms underlying the impairment are unknown. Activation of the infralimbic cortex (IL) in the medial prefrontal cortex (mPFC) has been reported to predict successful fear extinction, whereas functionally disrupting this region impairs extinction. We examined whether chemogenetic activation of the IL could alleviate impaired EFM in a single prolonged stress (SPS) rat model of PTSD.

METHODS

Chemogenetic activation of IL and prelimbic (PL) excitatory neurons was undertaken to evaluate EFM using a contextual fear conditioning paradigm. Neuronal activity in the IL was recorded using a 32-multichannel silicon electrode. To examine histological changes in the mPFC, apoptosis was measured by TUNEL staining.

RESULTS

Chemogenetic activation of excitatory neurons in the IL, but not the PL, enhanced EFM in sham rats and resulted in alleviation of EFM impairment in SPS rats. The alleviation of impaired EFM in SPS rats was observed during the extinction test session. Neuronal activity in the IL of SPS rats was lower than that of sham rats after clozapine-n-oxide administration. Increased apoptosis was found in the IL of SPS rats.

CONCLUSIONS

These findings suggest that a decreased excitatory response in the IL due, at least in part, to an increase in apoptosis in SPS rats leads to impaired EFM, and that neuronal activation during extinction training could be useful for the treatment of impaired EFM in PTSD patients.

GluN2D NMDA Receptors Gate Fear Extinction Learning and Interneuron Plasticity

The cerebellum is critically involved in the formation of associative fear memory and in subsequent extinction learning. Fear conditioning is associated with a long-term potentiation at both excitatory and inhibitory synapses onto Purkinje cells. We therefore tested whether fear conditioning unmasks novel forms of synaptic plasticity, which enable subsequent extinction learning to reset cerebellar circuitry. We found that fear learning enhanced GABA release from molecular layer interneurons and this was reversed after fear extinction learning. Importantly an extinction-like stimulation of parallel fibers after fear learning is sufficient to induce a lasting decrease in inhibitory transmission (I-LTD_stim) in the cerebellar cortex, a form of plasticity that is absent in naïve animals. While NMDA (N-methyl-D-aspartate) receptors are required for the formation and extinction of associative memory, the role of GluN2D, one of the four major NMDA receptor subunits, in learning and memory has not been determined. We found that fear conditioning elevates spontaneous GABA release in GluN2D KO as shown in WT mice. Deletion of GluN2D, however, abolished the I-LTD_stim induced by parallel fiber stimulation after learning. At the behavioral level, genetic deletion of GluN2D subunits did not affect associative learning and memory retention, but impaired subsequent fear extinction learning. D-cycloserine, a partial NMDA receptor (NMDAR) agonist, failed to rescue extinction learning in mutant mice. Our results identify GluN2D as a critical NMDAR subunit for extinction learning and reveal a form of GluN2D-dependent metaplasticity that is associated with extinction in the cerebellum.

The Associations Between Sleep and Externalizing and Internalizing Problems in Children and Adolescents with Attention-Deficit/Hyperactivity Disorder: Empirical Findings, Clinical Implications, and Future Research Directions

Sleep problems are common in youth with attention-deficit/hyperactivity disorder (ADHD). Externalizing and internalizing problems contribute to dysfunction in youth with ADHD and are amplified by disrupted sleep. This objective of this article is to synthesize empirical studies that examined the associations between sleep and internalizing or externalizing problems in individuals with ADHD. The main findings are that sleep problems precede, predict, and significantly contribute to the manifestation of internalizing and externalizing behavior problems among children and adolescents with ADHD. Clinicians should assess sleep and integrate sleep interventions into the management of youth with ADHD.

Where does fear originate in the brain? A coordinate-based meta-analysis of explicit and implicit fear processing

Processing of fear is of crucial importance for human survival and it can generally occur at explicit and implicit conditions. It is worth noting that explicit and implicit fear processing produces different behavioral and neurophysiological outcomes. The present study capitalizes on the Activation Likelihood Estimation (ALE) method of meta-analysis to identify: (a) the "core" network of fear processing in healthy individuals; (b) common and specific neural activations associated with explicit and implicit processing of fear. Following PRISMA guidelines, a total of 92 fMRI and PET studies were included in the meta-analysis. The overall analysis show that the core fear network comprises the amygdala, pulvinar, and fronto-occipital regions. Both implicit and explicit fear processing activated amygdala, declive, fusiform gyrus, and middle frontal gyrus, suggesting that these two types of fear processing share a common neural substrate. Explicit fear processing elicited more activations at the pulvinar and parahippocampal gyrus, suggesting visual attention/orientation and contextual association play important roles during explicit fear processing. In contrast, implicit fear processing elicited more activations at the cerebellum-amygdala-cortical pathway, indicating an 'alarm' system underlying implicit fear processing. These findings have shed light on the neural mechanism underlying fear processing at different levels of awareness.

Sleep Early After Trauma

Abstract. Posttraumatic stress disorder (PTSD) is characterized by intrusive re-experiencing of emotional memories of a traumatic event. Such memories are formed after exposure to trauma in the context of a cascading stress response including high levels of emotional arousal and stress hormone release. Sleep could be a key modulator of early memory formation and re-consolidation processes. Initial studies have investigated this association in this early time period, that is, hours and days after trauma exposure, and its role in modulating trauma memories and PTSD. The time is thus ripe to integrate findings from these studies. The current review consolidated evidence from five experimental and seven naturalistic studies on the association between trauma, sleep, and the development of intrusive emotional memories and PTSD, respectively. Together, the studies point to a potential protective role of sleep after trauma for the development of intrusive memories and PTSD. Findings regarding key sleep architecture features are more mixed and require additional investigation. The findings are important for prevention and intervention science.

An integrated model of chronic trauma-induced insomnia

Insomnia is the most commonly reported symptom of posttraumatic stress disorder (PTSD), with at least 70% of patients with PTSD reporting disturbed sleep. Although posttraumatic insomnia has traditionally been conceptualized as a consequence of PTSD, it is the most likely symptom to not remit following otherwise successful PTSD treatment. This suggests that the relationship between PTSD and insomnia is more complex, such that they likely share underlying pathological mechanisms and that factors non-specific to PTSD maintain chronic trauma-induced insomnia. Although several theories and hypotheses have been presented to explain the relationship between PTSD and insomnia, neurobiological and psychological models have not been integrated, thereby limiting their comprehensiveness and abilities to inform effective intervention. Further, existing models have not addressed how acute trauma-induced insomnia becomes chronic. The present review examined models of PTSD and insomnia separately, as well as existing theorized mechanisms of their co-morbidity. The distinct characteristics of trauma-induced insomnia were also reviewed and presented to describe the unique clinical presentation of trauma-induced insomnia. Review and integration of the literature were used to propose an integrated model of chronic trauma-induced insomnia informed by a neuropsychobiological framework. Clinical implications and future research directions are presented and discussed.

Adolescent Vulnerability to Heightened Emotional Reactivity and Anxiety After Brief Exposure to an Obesogenic Diet

BACKGROUND

Emerging evidence demonstrates that diet-induced obesity disrupts corticolimbic circuits underlying emotional regulation. Studies directed at understanding how obesity alters brain and behavior are easily confounded by a myriad of complications related to obesity. This study investigated the early neurobiological stress response triggered by an obesogenic diet. Furthermore, this study directly determined the combined impact of a short-term obesogenic diet and adolescence on critical behavioral and molecular substrates implicated in emotion regulation and stress.

METHODS

Adolescent (postnatal day 31) or adult (postnatal day 81) Lewis rats were fed for 1 week with an experimental Western-like high-saturated fat diet (WD, 41% kcal from fat) or a matched control diet (CD, 13% kcal from fat). We used the acoustic fear-potentiated startle (FPS) paradigm to determine the effects of the WD on cued fear conditioning and fear extinction. We used c-Fos mapping to determine the functional influence of the diet and stress on corticolimbic circuits.

RESULTS

We report that 1-week WD consumption was sufficient to induce fear extinction deficits in adolescent rats, but not in adult rats. We identify fear-induced alterations in corticolimbic neuronal activation and demonstrate increased prefrontal cortex CRHR1 messenger RNA (mRNA) levels in the rats that consumed the WD.

CONCLUSION

Our findings demonstrate that short-term consumption of an obesogenic diet during adolescence heightens behavioral and molecular vulnerabilities associated with risk for anxiety and stress-related disorders. Given that fear extinction promotes resilience and that fear extinction principles are the foundation of psychological treatments for posttraumatic stress disorder (PTSD), understanding how obesogenic environments interact with the adolescent period to affect the acquisition and expression of fear extinction memories is of tremendous clinical relevance.

The Neurochemical Effects of Prazosin Treatment on Fear Circuitry in a Rat Traumatic Stress Model

Objective

The timing of administration of pharmacologic agents is crucial in traumatic stress since they can either potentiate the original fear memory or may cause fear extinction depending on the phase of fear conditioning. Brain noradrenergic system has a role in fear conditioning. Data regarding the role of prazosin in traumatic stress are controversial.

Methods

In this study, we examined the effects of prazosin and the noradrenergic system in fear conditioning in a predator stress rat model. We evaluated the direct or indirect effects of stress and prazosin on noradrenaline (NA), gamma-aminobuytyric acid (GABA), glutamate, glycine levels and choline esterase activity in the amygdaloid complex, the dorsal hippocampus, the prefrontal cortex and the rostral pons.

Results

Our results demonstrated that prazosin might alleviate defensive behaviors and traumatic stress symptoms when given during the traumatic cue presentation in the stressed rats. However prazosin administration resulted in higher anxiety levels in non stressed rats when the neutral cue was presented.

Conclusion

Prazosin should be used in PTSD with caution because prazosin might exacerbate anxiety in non-traumatized subjects. However prazosin might as well alleviate stress responses very effectively. Stress induced changes included increased NA and GABA levels in the amygdaloid complex in our study, attributing noradrenaline a possible inhibitory role on fear acquisition. Acetylcholine also has a role in memory modulation in the brain. We also demonstrated increased choline esterase acitivity. Cholinergic modulation might be another target for indirect prazosin action which needs to be further studied.

Cortical oxygenation during exposure therapy - in situ fNIRS measurements in arachnophobia

•

This is the first study that assessed cortical hemodynamic reactions during exposure therapy in situ.

•

During exposure patients showed increased activity in the cognitive control network (CCN) compared to a control condition.

•

CCN activity deceased during the session.

•

Further, CCN activity was associated with fear ratings at the beginning of the session and this relationship decreased from session to session.

Exposure therapy is a well-studied and highly efficacious treatment for phobic disorders. Although the neurobiological model of fear is well underpinned by various studies, the mechanisms of exposure therapy are still under discussion. Partly, this is due to the fact that most neurophysiological methods like fMRI are not able to be used in the natural therapeutic settings.

The current study used in situ measurements of cortical blood oxygenation (O₂Hb) during exposure therapy by means of functional near-infrared spectroscopy. 37 subjects (N = 30 completers) underwent exposure therapy during 5 adapted sessions in which subjects were exposed to Tegenaria Domestica (domestic house spider – experimental condition) and Dendrobaena Veneta/ Eisenaia hortensis (red earthworm – control condition).

Compared to the control condition, patients showed higher O₂Hb levels in the anticipation and exposure phase of spider exposure in areas of the cognitive control network (CCN). Further, significant decreases in O₂Hb were observed during the session accompanied by reductions in fear related symptoms. However, while symptoms decreased in a linear quadratic manner, with higher reductions in the beginning of the session, CCN activity decreased linearly. Further, higher anxiety at the beginning of session one was associated with increased O₂Hb in the CCN. This association decreased within the following sessions.

The current study sheds light on the neuronal mechanisms of exposure therapy. The results are discussed in light of a phase model of exposure therapy that posits a role of cognitive control in the beginning and routine learning at the end of the therapy session.

Administration of moclobemide facilitates fear extinction and attenuates anxiety-like behaviors by regulating synaptic-associated proteins in a rat model of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is a long-lasting mental disorder and accompanied by worse fear extinction. Enhanced fear memory or poor fear extinction are typical features of PTSD. Dysfunction of the serotonergic neurotransmitter system is involved in numerous mental and behavioral disorders. Monoamine oxidase A (MAOA) is important in the metabolism of serotonin and play an important role in behavious. The aim of this study was to explore the change of MAOA and effect of MAOA on fear memory in PTSD. We used single prolonged stress (SPS) to create animal model of PTSD. A startle/fear box and elevated plus maze were used to observe fear memory and anxiety level, respectively. We examined the expression of MAOA and synaptic marker protein, as well as the immunological activity of MAOA in the infralimbic cortex (IL) area, which is a critical brain region involved in emotions, especially fear regulation. We found increased anxiety-like behavior, dysfunction in fear extinction, and increased MAOA in SPS rats. After treatment with moclobemide (a selective inhibitor of MAOA), SPS rats showed significantly improved fear memory and decreased anxiety-like behavior, which indicated that moclobemide could reverse fear extinction deficit and attenuate abnormally increased levels of anxiety caused by SPS in short term. On the contrary, decreased PSD-95 and SYN1 expression in the IL region were also reversed by moclobemide. These results suggest that increased MAOA play a negative role in fear extinction and levels of anxiety in PTSD, which may be involved in change in PSD-95 and SYN1.

Endocannabinoid modulating drugs improve anxiety but not the expression of conditioned fear in a rodent model of post-traumatic stress disorder

The endocannabinoid (eCB) system is a potential target for the treatment of symptoms of post-traumatic stress disorder (PTSD). Similar to clinical PTSD, approximately 25-30% of rats that undergo cued fear conditioning exhibit impaired extinction learning. In addition to extinction-resistant fear, these "weak extinction" (WE) rats show persistent anxiety-like behaviors. The goal of the present study was to test the hypothesis that behavioural differences between WE animals and those presenting normal extinction patterns (strong extinction; SE) could be mediated by the eCB system. Rats undergoing fear conditioning/extinction and fear recall sessions were initially segregated in weak and strong-extinction groups. Two weeks later, animals underwent a fear recall session followed by a novelty-suppressed feeding (NSF) test. In acute experiments, WE rats were injected with either the fatty acid amide hydrolase (FAAH) inhibitor URB597 or the CB1 agonist WIN55,212-2 1 h prior to long-term recall and NSF testing. SE animals were injected with the inverse CB₁ receptor agonist AM251. In chronic experiments, WE and SE rats were given daily injections of URB597 or AM251 between short and long-term recall sessions. We found that acute administration of WIN55,212-2 but not URB597 reduced anxiety-like behaviour in WE rats. In contrast, AM251 was anxiogenic in SE animals. Neither treatment was effective in altering freezing expression during fear recall. The chronic administration of AM251 to SE or URB597 to WE did not alter fear or anxiety-like behaviour or changed the expression of FAAH and CB₁. Together, these results suggest that systemic manipulations of the eCB system may alter anxiety-like behaviour but not the behavioural expression of an extinction-resistant associative fear memory.

Deconstructing the Gestalt: Mechanisms of Fear, Threat, and Trauma Memory Encoding

Threat processing is central to understanding debilitating fear- and trauma-related disorders such as posttraumatic stress disorder (PTSD). Progress has been made in understanding the neural circuits underlying the "engram" of threat or fear memory formation that complements a decades-old appreciation of the neurobiology of fear and threat involving hub structures such as the amygdala. In this review, we examine key recent findings, as well as integrate the importance of hormonal and physiological approaches, to provide a broader perspective of how bodily systems engaged in threat responses may interact with amygdala-based circuits in the encoding and updating of threat-related memory. Understanding how trauma-related memories are encoded and updated throughout the brain and the body will ultimately lead to novel biologically-driven approaches for treatment and prevention.

The loop neural circuit between the medial prefrontal cortex and the amygdala in the rat brain

A major neuronal basis underlying emotion regulation is the inhibitory influence of the medial prefrontal cortex (mPFC) on amygdalar neurons. However, in spite of the importance of mPFC neuronal activities in emotion regulation, little is known about the inputs modulating activity of mPFC neurons projecting to the amygdala. To gain insight into dense reciprocal connections between mPFC and amygdala, we investigated neural circuits between these brain regions using electrophysiological techniques. We found that mPFC neurons were antidromically driven mainly by stimulation of the central nucleus of the amygdala (CeA), rather than the posterior part of the basolateral nucleus of the amygdala (pBLA), whereas pBLA, but not CeA, stimulation evoked orthodromic excitatory and inhibitory responses. mPFC neurons antidromically driven by CeA stimulation showed excitatory or inhibitory responses to pBLA stimulation. These findings indicate the existence of a functional neural loop between amygdala and mPFC, pointing to an amygdalar self-control system.

Calretinin+-neurons-mediated GABAergic inhibition in mouse prefrontal cortex

The prefrontal cortex (PFC) is a center for executive and cognitive functions. Although many studies have been carried out to elucidate the role of different subtypes of GABAergic neurons in other brain areas, their functional relevance in PFC is still not fully understood. Calretinin⁺-GABAergic neurons are heterogeneous in their morphology and intrinsic properties. Previous studies showed an involvement of CR⁺-GABAergic neurons in the disinhibition of the other GABAergic neurons in neocortex and hippocampus. Furthermore, the loss of CR⁺- and PV⁺-interneurons in human brain has been linked to the vulnerability of the interneurons and to the overall increase in the network excitability associated with mental diseases. In the present study, the intensity of CR⁺-neuropil was higher in layer II/III, whereas the intensity of PV⁺-neuropil was higher in deeper layers within the PFC. In addition, pronounced CR expression was detected in layer II and III of prelimbic and infralimbic cortex whereas they were less abundant in anterior cingulate cortex and motor cortex 2. Our results showed that bipolar CR⁺- neurons in layer V not only feedback inhibited multipolar CR⁺- and other interneurons in layer II/III, but the majority of bipolar CR⁺-neurons in layer II/III also provide long-range forward-inhibition to pyramidal neurons in deeper layers of PFC. Thus, given the importance of the neuronal network of PFC in central control of emotion and cognition and in the pathology of mental diseases, CR⁺-GABAergic neuron-mediated feed-forward and -backward modulation within PFC would differentially modulate the downstream limbic activity and subsequently shape the cognitive and emotional behavior.

Fronto-Limbic Connectivity as a Predictor of Improvement in Nonsuicidal Self-Injury in Adolescents Following Psychotherapy

Objectives: Key neurobiological factors contribute to vulnerability to nonsuicidal self-injury (NSSI) among adolescents and how they respond to treatment targeted to reduce such behaviors. This study aims to examine differences in intrinsic functional connectivity between adolescents with NSSI and healthy controls (HCs) and to identify baseline connectivity markers that predict improvements in NSSI after psychotherapy. Methods: Adolescents aged 12-17 (n = 24) with repetitive NSSI along with demographically similar HCs (n = 16) underwent resting-state functional MRI scanning after which patients received up to 4 months of psychological treatment. A seed-based approach was used to examine baseline between-group differences in intrinsic functional connectivity of the amygdala and the medial prefrontal cortex (mPFC). Further analyses examined the associations between intrinsic functional connectivity at baseline and improvement in NSSI after psychological treatment. Results: Compared with HCs, adolescents with NSSI showed significantly reduced connectivity between the amygdala and the anterior cingulate cortex, subcallosal cortex, and paracingulate gyrus, as well as between the amygdala and a cluster encompassing the right planum temporale and right insula. Adolescents with NSSI, compared with HCs, also showed reduced connectivity between the mPFC and two clusters: one located in the precentral and postcentral gyri and another in the left insula. After treatment, 50% of patients reported fewer NSSI episodes compared to baseline, which was considered as improvement. Stronger negative amygdala-prefrontal connectivity was associated with greater posttreatment improvement in NSSI. Conclusions: Adolescents with NSSI may have aberrant amygdala and mPFC connectivity compared with HCs. Furthermore, stronger baseline negative amygdala-prefrontal connectivity may predict greater improvement in NSSI after psychological intervention. Given that no prior study has used resting-state functional connectivity to predict response to psychological treatment in adolescents with NSSI, replication of these findings is needed.

Infant Trauma Alters Social Buffering of Threat Learning: Emerging Role of Prefrontal Cortex in Preadolescence

Within the infant-caregiver attachment system, the primary caregiver holds potent reward value to the infant, exhibited by infants' strong preference for approach responses and proximity-seeking towards the mother. A less well-understood feature of the attachment figure is the caregiver's ability to reduce fear via social buffering, commonly associated with the notion of a "safe haven" in the developmental literature. Evidence suggests this infant system overlaps with the neural network supporting social buffering (attenuation) of fear in the adults of many species, a network known to involve the prefrontal cortex (PFC). Here, using odor-shock conditioning in young developing rats, we assessed when the infant system transitions to the adult-like PFC-dependent social buffering of threat system. Rat pups were odor-shock conditioned (0.55 mA-0.6 mA) at either postnatal day (PN18; dependent on mother) or 28 (newly independent, weaned at PN23). Within each age group, the mother was present or absent during conditioning, with PFC assessment following acquisition using 14C 2-DG autoradiography and cue testing the following day. Since the human literature suggests poor attachment attenuates the mother's ability to socially buffer the infants, half of the pups at each age were reared with an abusive mother from PN8-12. The results showed that for typical control rearing, the mother attenuated fear in both PN18 and PN28 pups, although the PFC [infralimbic (IL) and ventral prelimbic (vPL) cortices] was only engaged at PN28. Abuse rearing completely disrupted social buffering of pups by the mother at PN18. The results from PN28 pups showed that while the mother modulated learning in both control and abuse-reared pups, the behavioral and PFC effects were attenuated after maltreatment. Our data suggest that pups transition to the adult-like PFC social support circuit after independence from the mother (PN28), and this circuit remains functional after early-life trauma, although its effectiveness appears reduced. This is in sharp contrast to the effects of early life trauma during infancy, where social buffering of the infant is more robustly impacted. We suggest that the infant social buffering circuit is disengaged by early-life trauma, while the adolescent PFC-dependent social buffering circuit may use a safety signal with unreliable safety value.

Efficacy and mechanisms of non-invasive brain stimulation to enhance exposure therapy: A review

Though cognitive behavioral techniques are generally effective in the treatment of anxiety disorders, some people fail to benefit from exposure therapy or experience a return of fear after terminating exposure therapy. The burgeoning field of non-invasive brain stimulation provides a potential method of augmenting exposure therapy so that it is more effective. Successful exposure therapy is hypothesized to occur due to inhibition, and research suggests that brain stimulation can alter inhibitory learning and related processes. As such, one can reasonably posit that brain stimulation could be used to test the inhibitory learning theory of exposure therapy and to increase the efficacy of exposure therapy by inducing stronger inhibitory learning during exposures. Four known studies that pair brain stimulation with exposure therapy have yielded promising preliminary evidence in support of the therapeutic use of brain stimulation. In this review we describe research illustrating the mechanisms and efficacy of non-invasive brain stimulation to enhance the understanding of and outcomes produced by exposure therapy.

A model of amygdala function following plastic changes at specific synapses during extinction

The synaptic networks in the amygdala have been the subject of intense interest in recent times, primarily because of the role of this structure in emotion. Fear and its extinction depend on the workings of these networks, with particular interest in extinction because of its potential to ameliorate adverse symptoms associated with post-traumatic stress disorder. Here we place emphasis on the extinction networks revealed by recent techniques, and on the probable plasticity properties of their synaptic connections. We use modules of neurons representing each of the principal components identified as involved in extinction. Each of these modules consists of neural networks, containing specific ratios of excitatory and specialized inhibitory neurons as well as synaptic plasticity mechanisms appropriate for the component of the amygdala they represent. While these models can produce dynamic output, here we concentrate on the equilibrium outputs and do not model the details of the plasticity mechanisms. Pavlovian fear conditioning generates a fear memory in the lateral amygdala module that leads to activation of neurons in the basal nucleus fear module but not in the basal nucleus extinction module. Extinction protocols excite infralimbic medial prefrontal cortex neurons (IL) which in turn excite so-called extinction neurons in the amygdala, leading to the release of endocannabinoids from them and an increase in efficacy of synapses formed by lateral amygdala neurons on them. The model simulations show how such a mechanism could explain experimental observations involving the role of IL as well as endocannabinoids in different temporal phases of extinction.

A Rodent Model of Exposure Therapy: The Use of Fear Extinction as a Therapeutic Intervention for PTSD

The symptoms of post-traumatic stress disorder (PTSD) include cognitive impairment related to medial prefrontal cortical dysfunction. Indeed, a deficit of cognitive flexibility, i.e., an inability to modify previously learned thoughts and behaviors based on changes in the environment, may underlie many of the other symptoms of PTSD, such as changes in mood, hyper-arousal, intrusive thoughts, exaggerated and over-generalized fear, and avoidance behavior. Cognitive-behavioral therapies target the cognitive dysfunction observed in PTSD patients, training them to recalibrate stress-related perceptions, interpretations and responses. Preclinically, the extinction of conditioned fear bears resemblance to one form of cognitive therapy, exposure therapy, whereby an individual learns, through repeated exposure to a fear-provoking stimulus in a safe environment, that the stimulus no longer signals imminent threat, and their fear response is suppressed. In this review article, we highlight recent findings from our lab using fear extinction as a preclinical model of exposure therapy in rodents exposed to chronic unpredictable stress (CUS). We specifically focus on the therapeutic effects of extinction on stress-compromised set-shifting as a measure of cognitive flexibility, and active vs. passive coping behavior as a measure of avoidance. Finally, we discuss mechanisms involving activity and plasticity in the medial prefrontal cortex (mPFC) necessary for the therapeutic effects of extinction on cognitive flexibility and active coping.

Neuroscience Research and Mentoring in Puerto Rico: What Succeeds in This Environment?

Twenty years ago, I arrived in Puerto Rico from New York City to establish a neuroscience laboratory and research program on extinction of conditioned fear. The lab's first research paper appeared in the Journal of Neuroscience (Quirk et al., 2000) and has been cited >900 times. The success of this project in Puerto Rico far surpassed my original expectations. Therefore, I thought it might be useful to identify the factors responsible for this success, with the hope of facilitating the development of laboratories in diverse settings. A description of our lab practices is interspersed with personal statements from trainees hailing from Puerto Rico and other parts of Latin America. Creating an effective research and training environment depends less on the director's personality and more on the proper practice of activities that foster intellectual growth, such as journal clubs, lab meetings, and philosophy of science retreats. On a personal level, this project has been enormously gratifying. The unique environment in Puerto Rico fostered my best work, and I am very happy to have established my laboratory here.

A role for miR-132 in learned safety

Learned safety is a fear inhibitory mechanism, which regulates fear responses, promotes episodes of safety and generates positive affective states. Despite its potential as experimental model for several psychiatric illnesses, including post-traumatic stress disorder and depression, the molecular mechanisms of learned safety remain poorly understood, We here investigated the molecular mediators of learned safety, focusing on the characterization of miRNA expression in the basolateral amygdala (BLA). Comparing levels of 22 miRNAs in learned safety and learned fear trained mice, six safety-related miRNAs, including three members of the miR-132/-212 family, were identified. A gain-of-function approach based upon in-vivo transfection of a specific miRNA mimic, and miR-132/212 knock-out mice as loss-of-function tool were used in order to determine the relevance of miR-132 for learned safety at the behavioral and the neuronal functional levels. Using a designated bioinformatic approach, PTEN and GAT1 were identified as potential novel miR-132 target genes and further experimentally validated. We here firstly provide evidence for a regulation of amygdala miRNA expression in learned safety and propose miR-132 as signature molecule to be considered in future preclinical and translational approaches testing the transdiagnostic relevance of learned safety as intermediate phenotype in fear and stress-related disorders.

Preclinical studies of stress, extinction, and prefrontal cortex: intriguing leads and pressing questions

BACKGROUND

Stress is associated with cognitive and emotional dysfunction, and increases risk for a variety of psychological disorders, including depression and posttraumatic stress disorder. Prefrontal cortex is critical for executive function and emotion regulation, is a target for stress hormones, and is implicated in many stress-influenced psychological disorders. Extinction of conditioned fear provides an excellent model system for examining how stress-induced changes in corticolimbic structure and function are related to stress-induced changes in neural function and behavior, as the neural circuitry underlying this behavior is well characterized.

OBJECTIVES

This review examines how acute and chronic stress influences extinction and describes how stress alters the structure and function of the medial prefrontal cortex, a potential neural substrate for these effects. In addition, we identify important unanswered questions about how stress-induced change in prefrontal cortex may mediate extinction deficits and avenues for future research.

KEY FINDINGS

A substantial body of work demonstrates deficits in extinction after either acute or chronic stress. A separate and substantial literature demonstrates stress-induced neuronal remodeling in medial prefrontal cortex, along with several key neurohormonal contributors to this remodeling, and there is substantial overlap in prefrontal mechanisms underlying extinction and the mechanisms implicated in stress-induced dysfunction of-and neuronal remodeling in-medial prefrontal cortex. However, data directly examining the contribution of changes in prefrontal structure and function to stress-induced extinction deficits is currently lacking.

CONCLUSIONS

Understanding how stress influences extinction and its neural substrates as well as individual differences in this effect will elucidate potential avenues for novel interventions for stress-sensitive disorders characterized by deficits in extinction.

N-Methyl D-aspartate receptor subunit signaling in fear extinction

N-Methyl D-aspartate receptors (NMDAR) are central mediators of glutamate actions underlying learning and memory processes including those required for extinction of fear and fear-related behaviors. Consistent with this view, in animal models, antagonists of NMDAR typically impair fear extinction, whereas partial agonists have facilitating effects. Promoting NMDAR function has thus been recognized as a promising strategy towards reduction of fear symptoms in patients suffering from anxiety disorders and post-traumatic disorder (PTSD). Nevertheless, application of these drugs in clinical trials has proved of limited utility. Here we summarize recent advances in our knowledge of NMDAR pharmacology relevant for fear extinction, focusing on molecular, cellular, and circuit aspects of NMDAR function as they relate to fear extinction at the level of behavior and cognition. We also discuss how these advances from animal models might help to understand and overcome the limitations of existing approaches in human anxiety disorders and how novel, more specific, and personalized approaches might help advance future therapeutic strategies.

Combined brain-derived neurotrophic factor with extinction training alleviate impaired fear extinction in an animal model of post-traumatic stress disorder

Impaired fear memory extinction (Ext) is one of the hallmark symptoms of post-traumatic stress disorder (PTSD). However, since the precise mechanism of impaired Ext remains unknown, effective interventions have not yet been established. Recently, hippocampal-prefrontal brain-derived neurotrophic factor (BDNF) activity was shown to be crucial for Ext in naïve rats. We therefore examined whether decreased hippocampal-prefrontal BDNF activity is also involved in the Ext of rats subjected to a single prolonged stress (SPS) as a model of PTSD. BDNF levels were measured by enzyme-linked immunosorbent assay (ELISA), and phosphorylation of TrkB was measured by immunohistochemistry in the hippocampus and medial prefrontal cortex (mPFC) of SPS rats. We also examined whether BDNF infusion into the ventral mPFC or hippocampus alleviated the impaired Ext of SPS rats in the contextual fear conditioning paradigm. SPS significantly decreased the levels of BDNF in both the hippocampus and mPFC and TrkB phosphorylation in the ventral mPFC. Infusion of BDNF 24 hours after conditioning in the infralimbic cortex (ILC), but not the prelimbic cortex (PLC) nor hippocampus, alleviated the impairment of Ext. Since amelioration of impaired Ext by BDNF infusion did not occur without extinction training, it seems the two interventions must occur consecutively to alleviate impaired Ext. Additionally, BDNF infusion markedly increased TrkB phosphorylation in the ILC of SPS rats. These findings suggest that decreased BDNF signal transduction might be involved in the impaired Ext of SPS rats, and that activation of the BDNF-TrkB signal might be a novel therapeutic strategy for the impaired Ext by stress.

Avoidance Problems Reconsidered

Active avoidance is the prototypical paradigm for studying aversively-motivated instrumental behavior. However, avoidance research stalled amid heated theoretical debates and the hypothesis that active avoidance is essentially Pavlovian flight. Here I reconsider key "avoidance problems" and review neurobehavioral data collected with modern tools. Although the picture remains incomplete, these studies strongly suggest that avoidance has an instrumental component and is mediated by brain circuits that resemble appetitive instrumental actions more than Pavlovian fear reactions. Rapid progress may be possible if investigators consider important factors like safety signals, response-competition, goal-directed vs. habitual control and threat imminence in avoidance study design. Since avoidance responses likely contribute to active coping, this research has important implications for understanding human resilience and disorders of control.

Connectome-based individualized prediction of temperament trait scores

Temperament consists of multi-dimensional traits that affect various domains of human life. Evidence has shown functional connectome-based predictive models are powerful predictors of cognitive abilities. Putatively, individuals' innate temperament traits may be predictable by unique patterns of brain functional connectivity (FC) as well. However, quantitative prediction for multiple temperament traits at the individual level has not yet been studied. Therefore, we were motivated to realize the individualized prediction of four temperament traits (novelty seeking [NS], harm avoidance [HA], reward dependence [RD] and persistence [PS]) using whole-brain FC. Specifically, a multivariate prediction framework integrating feature selection and sparse regression was applied to resting-state fMRI data from 360 college students, resulting in 4 connectome-based predictive models that enabled prediction of temperament scores for unseen subjects in cross-validation. More importantly, predictive models for HA and NS could be successfully generalized to two relevant personality traits for unseen individuals, i.e., neuroticism and extraversion, in an independent dataset. In four temperament trait predictions, brain connectivities that show top contributing power commonly concentrated on the hippocampus, prefrontal cortex, basal ganglia, amygdala, and cingulate gyrus. Finally, across independent datasets and multiple traits, we show person's temperament traits can be reliably predicted using functional connectivity strength within frontal-subcortical circuits, indicating that human social and behavioral performance can be characterized by specific brain connectivity profile.

Modulating reconsolidation and extinction to regulate drug reward memory

Drug addiction is an aberrant memory that shares the same memory processes as other memories. Brief exposure to drug-associated cues could result in reconsolidation, a hypothetical process during which original memory could be updated. In contrast, longer exposure times to drug-associated cues could trigger extinction, a process that decreases the conditioned responding. In this review, we discuss the pharmacological and non-pharmacological manipulations on the reconsolidation and extinction that could be used to interfere with drug reward memories. Pharmacological agents such as β-adrenergic receptor antagonist propranolol can interfere with reconsolidation to disrupt drug reward memory. Pharmacological agents such as the NMDA receptor glycine site agonists d-cycloserine and d-serine can facilitate extinction and then attenuate the expression of drug reward memory. Besides pharmacological interventions, drug-free behavioral approaches by utilizing the reconsolidation and extinction, such as 'post-retrieval extinction' and 'UCS-retrieval extinction', are also effective to erase or inhibit the recall of drug reward memory. Taken together, pharmacological modulation and non-pharmacological modulation of reconsolidation and extinction are promising approaches to regulate drug reward memory and prevent relapse.

The BDNF Val66Met Prodomain Disassembles Dendritic Spines Altering Fear Extinction Circuitry and Behavior

A human variant in the BDNF gene (Val66Met; rs6265) is associated with impaired fear extinction. Using super-resolution imaging, we demonstrate that the BDNF Met prodomain disassembles dendritic spines and eliminates synapses in hippocampal neurons. In vivo, ventral CA1 (vCA1) hippocampal neurons undergo similar morphological changes dependent on their transient co-expression of a SorCS2/p75^NTR receptor complex during peri-adolescence. BDNF Met prodomain infusion into the vCA1 during this developmental time frame reduces dendritic spine density and prelimbic (PL) projections, impairing cued fear extinction. Adolescent Bdnf^Met/Met mice display similar spine and PL innervation deficits. Using fiber photometry, we found that, in wild-type mice, vCA1 neurons projecting to the PL encode extinction by enhancing neural activity in threat anticipation and rapidly subsiding their response. This adaptation is absent in BDNF^Met/Met mice. We conclude that the BDNF Met prodomain renders vCA1-PL projection neurons underdeveloped, preventing their capacity for subsequent circuit modulation necessary for fear extinction. VIDEO ABSTRACT.

Impulsive aggression and response inhibition in attention-deficit/hyperactivity disorder and disruptive behavioral disorders: Findings from a systematic review

BACKGROUND

Although impulsive aggression (IA) and dysfunctional response inhibition (RI) are hallmarks of attention-deficit/hyperactivity disorder (ADHD) and disrupted behavioral disorders (DBDs), little is known about their shared and distinct deviant neural mechanisms.

AIMS AND METHODS

Here, we selectively reviewed s/fMRI ADHD and DBD studies to identify disorder-specific and shared IA and RI aberrant neural mechanisms.

RESULTS

In ADHD, deviant prefrontal and cingulate functional activity was associated with increased IA. Structural alterations were most pronounced in the cingulate cortex. Subjects with DBDs showed marked cortico-subcortical dysfunctions. ADHD and DBDs share similar cortico-limbic structural and functional alterations. RI deficits in ADHD highlighted hypoactivity in the dorso/ventro-lateral PFC, insula, and striatum, while the paralimbic system was primarily dysfunctional in DBDs. Across disorders, extensively altered cortico-limbic dysfunctions underlie IA, while RI was mostly associated with aberrant prefrontal activity.

CONCLUSION

Control network deficits were evidenced across clinical phenotypes in IA and RI. Dysfunctions at any level within these cortico-subcortical projections lead to deficient cognitive-affective control by ascribing emotional salience to otherwise irrelevant stimuli. The clinical implications of these findings are discussed.

Sex differences in extinction to negative stimuli: Event-related brain potentials

There are controversial observations regarding whether females have a longer time to extinction than men, which may be related to different levels of conditioning acquisition and/or the influence of the menstrual cycle. We explored the electrophysiological evidence of sex differences in extinction.In this study, females in the luteal phase and menstrual phase were examined for event-related potential (ERP) and evidence of attention allocation in the conditioning model using electroencephalogram recordings. A group of male participants was also included and compared.Women in the luteal phase had a higher difference waveform of P3 amplitude to conditioned stimulus (CS) in the extinction phase than women in the menstrual phase and men. There was a shorter latency of P3 to CS+ in men than in women in the extinction phase, suggesting that men react faster than women to unconditioned stimulus (US) expectation. Our study revealed that women in the luteal phase allocated more attentive resources to the expectation of a US. In contrast, men displayed faster expectation of the extinguished US than women. Our results support the superiority of ERP technology in documenting the neural mechanism of the extinction process.