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Preclinical research suggests that enhancing CB1 receptor agonism may improve fear extinction. In order to translate this knowledge into a clinical application we examined whether cannabidiol (CBD), a hydrolysis inhibitor of the endogenous CB1 receptor agonist anandamide (AEA), would enhance the effects of exposure therapy in treatment refractory patients with anxiety disorders. Patients with panic disorder with agoraphobia or social anxiety disorder were recruited for a double-blind parallel randomised controlled trial at three mental health care centres in the Netherlands. Eight therapist-assisted exposure in vivo sessions (weekly, outpatient) were augmented with 300 mg oral CBD (n = 39) or placebo (n = 41). The Fear Questionnaire (FQ) was assessed at baseline, mid-and post-treatment, and at 3 and 6 months follow-up. Primary analyses were on an intent-to-treat basis. No differences were found in treatment outcome over time between CBD and placebo on FQ scores, neither across (beta = 0.32, 95% CI [-0.60; 1.25]) nor within diagnosis groups (beta = -0.11, 95% CI [-1.62; 1.40]). In contrast to our hypotheses, CBD augmentation did not enhance early treatment response, within-session fear extinction or extinction learning. Incidence of adverse effects was equal in the CBD (n = 4, 10.3%) and placebo condition (n = 6, 15.4%). In this first clinical trial examining CBD as an adjunctive therapy in anxiety disorders, CBD did not improve treatment outcome. Future clinical trials may investigate different dosage regimens. (c) 2022 Published by Elsevier B.V.

This page contains the links to the preregistration and clinical trial registration of the human study that is part of https://osf.io/ydwba.

Altres ajuts: acords transformatius de la UAB Altres ajuts: Swiss National Science Foundation (SNSF) [NCCR Synapsy grant: 51NF40-158776 and − 185897] Posttraumatic stress disorder (PTSD) is a highly disabling psychiatric condition that may arise after exposure to acute and severe trauma. It is a highly prevalent mental disorder worldwide, and the current treatment options for these patients remain limited due to low effectiveness. The time window right after traumatic events provides clinicians with a unique opportunity for preventive interventions against potential deleterious alterations in brain function that lead to PTSD. Some studies pointed out that PTSD patients present an abnormal function of the hypothalamic-pituitary-adrenal axis that may contribute to a vulnerability toward PTSD. Moreover, glucocorticoids have arisen as a promising option for preventing the disorder's development when administered in the aftermath of trauma. The present work compiles the recent findings of glucocorticoid administration for the prevention of a PTSD phenotype, from human studies to animal models of PTSD. Overall, glucocorticoid-based therapies for preventing PTSD demonstrated moderate evidence in terms of efficacy in both clinical and preclinical studies. Although clinical studies point out that glucocorticoids may not be effective for all patients' subpopulations, those with adequate traits might greatly benefit from them. Preclinical studies provide precise insight into the mechanisms mediating this preventive effect, showing glucocorticoid-based prevention to reduce long-lasting behavioral and neurobiological abnormalities caused by traumatic stress. However, further research is needed to delineate the precise mechanisms and the extent to which these interventions can translate into lower PTSD rates and morbidity.

We hypothesize that the cerebellum is involved in the processing of reward prediction errors in cooperation with the ventral tegmental area (VTA), and that these reward prediction errors drive fear extinction learning. To study this proposed interaction, we use a 3-day fear conditioning paradigm in young and healthy controls in a 7T MRI scanner. Fear extinction is studied through Pavlovian fear conditioning paradigms, in which the presentation of a neutral conditioned stimulus (CS) is paired to an aversive unconditioned stimulus (US), so that a fear association is learned between the CS and the US. As a result, the CS is no longer neutral and generates a conditioned fear response (e.g. increased sweating and enlarged pupil size). When the CS is subsequently no longer paired with the US, fear extinction learning occurs, which inhibits the fear association and dampens the conditioned fear response. An important event for fear extinction learning is the unexpected omission of the US, which is a better than expected outcome, resulting in reward prediction errors (Kalisch et al., 2019). Research on rodents has shown that the VTA encodes these reward prediction errors during fear extinction (Salinas-Hernández et al., 2018). On the other hand, the cerebellum is known to process prediction errors in the motor domain, and this is increasingly thought to be true for cognitive and emotional domains as well (Popa and Ebner, 2019). In accordance with this, Ernst and colleagues found that the human cerebellum has prediction error related activity during the unexpected omission of the US (Ernst et al., 2019). In addition, the cerebellum and the VTA are connected bidirectionally (Ikai et al., 1992; Carta et al., 2019). Taken together, an interaction between the cerebellum and VTA might be important to process reward prediction errors which could drive fear extinction.

Preregistrations and data related to Luyten et al., 2023.

Persistent cognitive impairment(s) can be a significant consequence of traumatic brain injury (TBI) and can markedly compromise quality of life. Unfortunately, identifying effective treatments to alleviate memory impairments in the chronic stage of TBI has proven elusive. Several studies have demonstrated that insulin-like growth factor-2 (IGF-2) can enhance memory in both normal animals and in experimental models of disease. In this study, we questioned whether IGF-2, when administered before learning, could enhance memory performance in the chronic stage of TBI. Male C57BL/6 mice (n = 7 per group) were injured using an electronic cortical impact injury device. Four months later, mice were tested for their cognitive performance in the fear memory extinction, novel object recognition (NOR), and Morris water maze tasks. Twenty minutes before each day of training, mice received a subcutaneous injection of either 30 μg/kg of IGF-2 or an equal volume of vehicle. Memory testing was carried out 24 h after training in the absence of the drug. Uninjured sham animals treated with IGF-2 (or vehicle) were trained and tested in the fear memory extinction task as a positive control. Our data show that although IGF-2 (30 μg/kg) improved memory extinction in uninjured mice, it was ineffective at improving fear memory extinction in the chronic stage of TBI. Similarly, IGF-2 administration to chronically injured animals did not improve TBI-related deficits in either NOR or spatial memory. Our results indicate that IGF-2, administered in the chronic stage of injury, is ineffective at enhancing memory performance and therefore may not be a beneficial treatment option for lingering cognitive impairments after a TBI.

IntroductionThreat processing, enabled by threat circuits, is supported by a remarkably conserved neural architecture across mammals. Threatening stimuli relevant for most species include the threat of being attacked by a predator or an aggressive conspecific and the threat of pain. Extensive studies in rodents have associated the threats of pain, predator attack and aggressive conspecific attack with distinct neural circuits in subregions of the amygdala, the hypothalamus and the periaqueductal gray. Bearing in mind the considerable conservation of both the anatomy of these regions and defensive behaviors across mammalian species, we hypothesized that distinct brain activity corresponding to the threats of pain, predator attack and aggressive conspecific attack would also exist in human subcortical brain regions.MethodsForty healthy female subjects underwent fMRI scanning during aversive classical conditioning. In close analogy to rodent studies, threat stimuli consisted of painful electric shocks, a short video clip of an attacking bear and a short video clip of an attacking man. Threat processing was conceptualized as the expectation of the aversive stimulus during the presentation of the conditioned stimulus.ResultsOur results demonstrate differential brain activations in the left and right amygdala as well as in the left hypothalamus for the threats of pain, predator attack and aggressive conspecific attack, for the first time showing distinct threat-related brain activity within the human subcortical brain. Specifically, the threat of pain showed an increase of activity in the left and right amygdala and the left hypothalamus compared to the threat of conspecific attack (pain > conspecific), and increased activity in the left amygdala compared to the threat of predator attack (pain > predator). Threat of conspecific attack revealed heightened activity in the right amygdala, both in comparison to threat of pain (conspecific > pain) and threat of predator attack (conspecific > predator). Finally, for the condition threat of predator attack we found increased activity in the bilateral amygdala and the hypothalamus when compared to threat of conspecific attack (predator > conspecific). No significant clusters were found for the contrast predator attack > pain.ConclusionResults suggest that threat type-specific circuits identified in rodents might be conserved in the human brain.

Background Enhancement of N-methyl-D-aspartate (NMDA) receptor function using glycine-site agonist D-cycloserine is known to facilitate fear extinction, providing a means to augment cognitive behavioral therapy in anxiety disorders. A novel class of glycine-site agonists has recently been identified, and we have found that the prototype, AICP, is more effective than D-cycloserine in modulating neuronal function. Methods Using novel glycine-site agonist AICP, local infusion studies, and genetic models, we elucidated the role of GluN2C-containing receptors in fear extinction. Results We tested the effect of intracerebroventricular injection of AICP on fear extinction and found a robust facilitation of fear extinction. This effect was dependent on GluN2C subunit, consistent with superagonist action of AICP at GluN2C-containing receptors. Local infusion studies in wild-type and GluN2C knockout mice suggested that AICP produces its effect via GluN2C-containing receptors in the basolateral amygdala (BLA). Furthermore, consistent with astrocytic expression of GluN2C subunit in the amygdala, we found that AICP did not facilitate fear extinction in mice with conditional deletion of obligatory GluN1 subunit from astrocytes. Importantly, chemogenetic activation of astrocytes in the basolateral amygdala facilitated fear extinction. Acutely, AICP was found to facilitate excitatory neurotransmission in the BLA via presynaptic GluN2C-dependent mechanism. Immunohistochemical studies suggest that AICP-mediated facilitation of fear extinction involves synaptic insertion of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor GluA1 subunit. Conclusion These results identify a unique role of astrocytic NMDA receptors composed of GluN2C subunit in extinction of conditioned fear memory and demonstrate that further development of recently identified superagonists of GluN2C-containing receptors may have utility for anxiety disorders.

Fear memories are necessary to initiate anticipatory fear responses when we are confronted with cues that predict an impending threat. However, when a cue no longer predicts threat, an extinction memory is formed that actively inhibits the expression of the fear memory. Failure to acquire, consolidate, or recall extinction memories causes fear memory expression (i.e., fear responding) in the absence of threat, which is a hallmark characteristic of most anxiety-related disorders and post-traumatic stress disorder (PTSD). Of further importance, these disorders occur approximately twice as often in women than men, which is thought to partially rely on sex hormone mediated differences in fear extinction. Moreover, deficits in extinction memory processing can also hinder the success of extinction-based exposure therapy, which is commonly used to treat these disorders. Thus, a better understanding of the factors determining the quality of extinction memories is of utmost importance. The present thesis focuses on three of these factors including the female sex hormone 17β-estradiol (E2), fear extinction timing, and the noradrenergic arousal system. To examine the role of E2 (Manuscript 1; low E2 levels or high E2 levels) and fear extinction timing (Manuscript 2; either immediately or delayed after the initial fear memory formation), we used a special differential fear conditioning procedure that allowed us to separately assess fear memories and extinction memories via peripheral arousal responses (measured via skin conductance responses [SCR]) and, most importantly, via central neurophysiological indicators (measured via electroencephalography [EEG]). Concerning EEG parameters, we were especially interested in neural oscillations (especially in the theta and gamma range). To further advance the understanding of the neurophysiological foundations of both memory systems, we also aimed at disentangling oscillatory and non-oscillatory brain activity (Manuscript 2). Moreover, the crucial role of the noradrenergic arousal system for the quality of extinction memories is highlighted in a review of relevant rodent and human studies (Manuscript 3). By using the described multi-methodological approach, we were able to demonstrate for the first time that peripheral arousal as well as fear-related theta oscillations are sensitive to E2. This was indicated by less fear responding (attenuated peripheral arousal and attenuated theta oscillations) during the recall of fear and extinction memories under high peripheral E2 levels (Manuscript 1). Concerning the role of fear extinction timing, we demonstrate that delayed extinction is advantageous over immediate extinction in reducing peripheral arousal during the recall of the extinction memory (Manuscript 2). Additionally, by disentangling oscillatory and non-oscillatory brain activity, we demonstrate for the first time that oscillatory and non-oscillatory brain activity is sensitive to fear expression. Moreover, by reviewing different rodent and human studies, we highlight the important role of noradrenergic arousal for the recall of extinction memories and, importantly, provide a detailed mechanistic framework of how extinction deficits might be caused after immediate extinction (Manuscript 3). In sum, the present thesis underscores the important role of E2, fear extinction timing, and the noradrenergic system for the recall quality of fear memories and extinction memories in humans.

The extinction of threat expectancies is a fragile phenomenon, as these threats may relapse. There are different reasons about why this relapse takes place. A fundamental issue in the study of extinction processes is to understand why relapse occurs and how it can be effectively prevented. This has led to an increasing interest in the study of new extinction strategies that could shed some light on this matter (Vervliet, Craske, & Hermans, 2013). In the present proposal, using a standard three-phase conditioning protocol (i.e., acquisition, intervention, test), we will try to evaluate, in humans, the effect deconditioning. This novel technique consists of a gradual reduction in the US intensity (an electric shock) across the intervention session so that by its end the US will be still presented but will have no relevant arousing effect as measured by SCR. Popik et al. (2020) found that their “deconditioning-update” preparation was able to reduce spontaneous recovery and renewal in a series of eight animal conditioning experiments. These authors suggest that reducing the mismatch between acquisition and intervention may promote memory updating rather than extinction. Their procedure aimed at weakening the original fear memory by updating the aversive information. To do this, they reactivated the fear memory with CSs presentations paired with an attenuated version of the originally highly aversive US. The deconditioning treatment described here should selectively eliminate the threat nature of the US, though its probability conditional to the presence of the CS will not be affected as it will be the same as it was during the acquisition phase. Note that some form of electrical stimulation will still be present at the end of the extinction phase even if it does not have any threatening effect for the participant. The current proposal differs from a deflation or devaluation procedure (Davey, 1992; Haesen & Vervliet, 2015; Hosoba et al., 2001; Leer et al., 2018) in the sense that the CS is still presented alongside the US and suggests that a deconditioning process may promote the modification of the original fear memory by means of gradually decreasing the threat it represents. Nevertheless, we would contrast the deconditioning hypothesis with a habituation-like mechanism, as proposed by Haesen & Vervliet (2015) and Leer et al. (2018), by including an additional CS+ that will not undergo treatment but will be tested afterwards. If habituation accounts for the benefit of a deconditioning treatment, fear should also be reduced for the CS+ that did not undergo treatment.

Objective(s): Treatments that reverse deficits in fear extinction are promising for the management of post-traumatic stress disorder (PTSD). 5-Hydroxytryptamine type 3 (5-HT3) receptor is involved involved in the extinction of fear memories. The present work aims to investigate the role of 5HT3 receptors in the infralimbic part of the medial prefrontal cortex (IL-mPFC) in extinction of conditioned fear in the single prolonged stress (SPS) model of PTSD in rats. Materials and Methods: The effect of SPS administration was evaluated on the freezing behavior in contextual and cued fear conditioning models. After the behavioral tests, levels of 5HT3 transcription in IL-mPFC were also measured in the same animals using the real-time RT-PCR method. To evaluate the possible role of local 5HT3 receptors on fear extinction, conditioned freezing was evaluated in another cohort of animals that received local microinjections of ondansetron (a 5HT3 antagonist) and ondansetron plus a 5HT3 agonist (SR 57227A) after extinction sessions. Results: Our findings showed that exposure to SPS increased the freezing response in both contextual and cued fear models. We also found that SPS is associated with increased expression of 5HT3 receptors in the IL-mPFC region. Ondansetron enhanced the fear of extinction in these animals and the enhancement was blocked by the 5HT3 agonist, SR 57227A. Conclusion: It seems that up-regulation of 5HT3 receptors in IL-mPFC is an important factor in the neurobiology of PTSD and blockade of these receptors could be considered a potential treatment for this condition.

Background: Trauma-based psychotherapy is a first line treatment for post-traumatic stress disorder (PTSD) but not all patients achieve long-term remission. Transcranial direct current stimulation (tDCS) received considerable attention as a neuromodulation method that may improve trauma-based psychotherapy. Objective: We explored the effects of repeated anodal tDCS over the prefrontal cortex (PFC) on fear extinction in mice as a preclinical model for trauma-based psychotherapy. Methods: We performed auditory fear conditioning with moderate or high shock intensity on C57BL6/J mice. Next, mice received anodal tDCS (0.2 mA, 20 min) or sham stimulation over the PFC twice daily for five consecutive days. Extinction training was performed by repeatedly exposing mice to the auditory cue the day after the last stimulation session. Early and late retention of extinction were evaluated one day and three weeks after extinction training respectively. Results: We observed no significant effect of tDCS on the acquisition or retention of fear extinction in mice subjected to fear conditioning with moderate intensity. However, when the intensity of fear con-ditioning was high, tDCS significantly lowered freezing during the acquisition of extinction, regardless of the extinction protocol. Moreover, when tDCS was combined with a strong extinction protocol, we also observed a significant improvement of early extinction recall. Finally, we found that tDCS reduced generalized fear induced by contextual cues when the intensity of conditioning is high and extinction training limited. Conclusions: Our data provide a rationale to further explore anodal tDCS over the PFC as potential support for trauma-based psychotherapy for PTSD. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Disruption of sleep due to acute or chronic stress can lead to changes in emotional memory processing. Sleep disturbances are highly prevalent in post-traumatic stress disorder (PTSD), but still, the contribution of sleep deprivation on the susceptibility to PTSD has received little attention. To determine whether rapid eye movement sleep deprivation (SD) alters the development of fear expression or fear-associated memory impairment in adolescent rats, we performed animal emotional behavior tests using an SD animal model with the flowerpot technique. SD rats showed an increase in locomotor activity frequency and a decrease in sucrose consumption compared to control rats. An increase in freezing behavior during shock trials was observed in SD rats. Noticeably, it was observed that when applying the SD condition after fear stimuli exposure, fear extinction was delayed more in SD rats than in control rats. Overall, these results indicate that SD in adolescent rats leads to increased locomotor activity and anhedonic behavior, as well as increased fear expression and delayed fear extinction, suggesting that SD would lead to increased severity of PTSD-like phenotype.

In combination with psychotherapy or in monotherapy, psychotropics are commonly used to treat anxiety. However, the mechanisms through which these agents promote behavior modification, and hence clinical improvement, or interact with behavioral techniques, are still unknown. In Humans, the assessment of behavior is highly limited by the hardship of obtaining reliable peripheral measures. To overcome such limitations, functional neuroimaging techniques have become an important research tool in this field. In addition, the psychiatric scientific community has joined efforts to create new diagnostic classification systems beyond the current categories that have been shown to be insufficient for the neurobiological understanding of the psychiatric manifestations. Therefore, our objective is to create an integrative lab environment to collect and analyze data from behavioral experiments, clinical trials and functional neuroimaging, not restricted to a single disorder. In our first project, we will investigate the performance on a fear conditioning paradigm during fMRI acquisition, before and after treatment with antidepressants for anxiety symptoms. Once the essential technology to such investigation is set, we plan to expand the use of behavioral paradigms to assess the effect of other psychotropics in specific psychiatric symptoms. Such understanding may be essential for the improvement of current treatment strategies as well as for the development of new therapeutic interventions.

Positive affect is hypothesized to improve safety learning taking place during extinction (i.e., the core mechanism of exposure treatment), therefore improving the maintenance of treatment outcomes. We investigated whether positive affect during extinction attenuates the subsequent return of pain-related avoidance and fear. In an operant pain-related avoidance conditioning paradigm, sixty healthy volunteers performed arm-reaching movements using a robotic arm. During acquisition, they learned to avoid an easy but painful movement (T1) by choosing more effortful movements that were sometimes (T2) or never (T3) painful. Then, the Positive affect group wrote about and imagined their best possible self, which is known to induce positive affect, whereas the Control group wrote about and imagined a typical day. During extinction with response prevention (RPE), participants were only allowed to perform T1, which was no longer paired with pain. Next, two painful stimuli were presented when participants were not moving (i.e., reinstatement manipulation). During test, all movements were available, and we examined whether fear and avoidance of the previously painful movements would re-emerge. Pain-related avoidance returned in both groups, but the two groups did not differ herein. The Positive affect group reported increased positive affect, though not more than the Control group. Nevertheless, they generalized the learned safety of T1 to the other movements during RPE, whereas they also retrospectively rated the pain as less intense and less unpleasant. These results add to the literature of positive affect as a resilience factor. ispartof: Behaviour Research And Therapy vol:153 pages:1-9 ispartof: location:England status: published

Ginsenoside Rg1 is efficient to prevent or treat mental disorders. However, the mechanisms underlying the effects of ginsenoside Rg1 on post-traumatic stress disorder (PTSD) are still not known. In this study, single-prolonged stress (SPS) regime, as well as injection of lipopolysaccharide (LPS), was used to produce PTSD-like behaviors in C57 mice, and the effects of ginsenoside Rg1 (10, 20, 40 mg/kg/d, ip, for 14 days) on PTSD-like behaviors were evaluated. Our results showed that ginsenoside Rg1 promoted fear extinction and prevented depression-like behaviors in both LPS and SPS models. Importantly, ginsenoside Rg1 alleviated LPS- or SPS-stimulated expression of pro-inflammatory cytokines (IL-1β and TNF-α), activation of astrocytes and microglia, and reduction of hippocampal synaptic proteins (PSD95, Arc, and GluA1). Ginsenoside Rg1 also reduced the increase of hippocampal Kir4.1 and GluN2A induced by PTSD regime. Importantly, reducing hippocampal astroglial Kir4.1 expression promoted fear extinction and improved depression-like behaviors in LPS-treated mice. Additionally, intracerebroventricular injection of TNF-α caused an impairment of fear extinction and promoted Kir4.1 expression in the hippocampus. Together, our study reveals novel protective effects of ginsenoside Rg1 against PTSD-like behaviors in mice, likely via promoting synaptic proteins, reducing Kir4.1 and TNF-α in the hippocampus.

Background Posttraumatic stress disorder (PTSD) may stem from the formation of aberrant and enduring aversive memories. Some PTSD patients have recreationally used Cannabis, probably aiming at relieving their symptomatology. However, it is still largely unknown whether and how Cannabis or its psychotomimetic compound Δ9-tetrahydrocannabinol (THC) attenuates the aversive/traumatic memory outcomes. Here, we seek to review and discuss the effects of THC on aversive memory extinction and anxiety in healthy humans and PTSD patients. Methods Medline, PubMed, Cochrane Library, and Central Register for Controlled Trials databases were searched to identify peer-reviewed published studies and randomized controlled trials in humans published in English between 1974 and July 2020, including those using only THC and THC combined with cannabidiol (CBD). The effect size of the experimental intervention under investigation was calculated. Results At low doses, THC can enhance the extinction rate and reduce anxiety responses. Both effects involve the activation of cannabinoid type-1 receptors in discrete components of the corticolimbic circuitry, which could couterbalance the low “endocannabinoid tonus” reported in PTSD patients. The advantage of associating CBD with THC to attenuate anxiety while minimizing the potential psychotic or anxiogenic effect produced by high doses of THC has been reported. The effects of THC either alone or combined with CBD on aversive memory reconsolidation, however, are still unknown. Conclusions Current evidence from healthy humans and PTSD patients supports the THC value to suppress anxiety and aversive memory expression without producing significant adverse effects if used in low doses or when associated with CBD. Future studies are guaranteed to address open questions related to their dose ratios, administration routes, pharmacokinetic interactions, sex-dependent differences, and prolonged efficacy.

There are few medications with demonstrated efficacy for the treatment of posttraumatic stress disorder (PTSD). Treatment guidelines have unequivocally designated psychotherapy as a first line treatment for PTSD. Yet, even after psychotherapy, PTSD often remains a chronic illness, with high rates of psychiatric and medical comorbidity. Meanwhile, the search for and development of drugs with new mechanisms of action has stalled. Therefore, there is an urgent need to explore not just novel compounds but novel approaches for the treatment of PTSD. A promising new approach involves the use of psychedelic drugs. Within the past few years, 2 psychedelics have received breakthrough designations for psychiatric indications from the US Food and Drug Administration, and several psychedelics are currently being investigated for the treatment of PTSD. This review discusses 4 types of compounds: 3,4-methylenedioxymethamphetamine, ketamine, classical psychedelics (e.g., psilocybin and lysergic acid diethylamide), and cannabinoids. We describe the therapeutic rationale, the setting in which they are being administered, and their current state of evidence in the treatment of PTSD. Each compound provides unique qualities for the treatment of PTSD, from their use to rapidly target symptoms to their use as adjuncts to facilitate psychotherapeutic treatments. Several questions are formulated that outline an agenda for future research.

Objective To explore the role of transient receptor potential canonical 6 (TRPC6) on conditioning and extinction in contextual fear memory. Methods A total of 32 male C57BL/6J mice (6~8 weeks old) were randomized into fear conditioning (Cond group, n=16) and fear extinction (Ext group, n=16). Both groups were further divided into sh-TRPC6 subgroup (n=8) and GFP subgroup (n=8). Stereotaxic injection of adeno-associated virus (AAV)-TRPC6 or AAV-green fluorescent protein (AAV-GFP) was performed into the hippocampus of the corresponding mice bilaterally for intervention of fear. Immunofluorescence assay and Western blotting were used to detect the expression of TRPC6 in hippocampus of each sub-group in 20 d after stereotaxic injection. On day 21, fear conditioning was established though inescapable foot shock (footshock of 0.7 mA for 2 s and intertrial interval for 58 s, totally 5 cycles), and fear test was carried out on day 22. For the mice from the Ext group, fear conditioning begun in 4 d after stereotaxic injection, fear extinction training started on day 21, and fear test was also carried out on day 22. Results At 20 d after injection, massive GFP-positive cells were observed in the pyramidal layer of hippocampal CA1 region, and Western blotting showed AAV-TRPC6 injection significantly reduced the hippocampal TRPC6 expression in the sh-TRPC6 subgroup than the GFP subgroup (P < 0.01). In the experiment of fear conditioning, the upward trend of the Freezing% levels in sh-TRPC6 subgroup was obviously slower (P < 0.05), and its Freezing% levels were notably lower in fear test when compared with the GFP subgroup (P < 0.05). In the experiment of fear extinction, the downward trend of the Freezing% levels in sh-TRPC6 subgroup was significantly slower (P < 0.05) and its Freezing% levels were significantly higher in fear test when compared with the GFP subgroup (P < 0.05). Conclusion Hippocampal TRPC6 participates in the conditioning and extinction in contextual fear memory, and suppression of its expression can destroy the processes.

There are few medications with demonstrated efficacy for the treatment of posttraumatic stress disorder (PTSD). Treatment guidelines have unequivocally designated psychotherapy as a first line treatment for PTSD. Yet, even after psychotherapy, PTSD often remains a chronic illness, with high rates of psychiatric and medical comorbidity. Meanwhile, the search for and development of drugs with new mechanisms of action has stalled. Therefore, there is an urgent need to explore not just novel compounds but novel approaches for the treatment of PTSD. A promising new approach involves the use of psychedelic drugs. Within the past few years, 2 psychedelics have received breakthrough designations for psychiatric indications from the US Food and Drug Administration, and several psychedelics are currently being investigated for the treatment of PTSD. This review discusses 4 types of compounds: 3,4-methylenedioxymethamphetamine, ketamine, classical psychedelics (e.g., psilocybin and lysergic acid diethylamide), and cannabinoids. We describe the therapeutic rationale, the setting in which they are being administered, and their current state of evidence in the treatment of PTSD. Each compound provides unique qualities for the treatment of PTSD, from their use to rapidly target symptoms to their use as adjuncts to facilitate psychotherapeutic treatments. Several questions are formulated that outline an agenda for future research.

Extinction learning is assumed to represent a core mechanism underlying exposure therapy. Empirical evaluations of this assumption, however, are largely lacking. The current study investigated whether neural activations and self-report outcomes during extinction learning and extinction recall could specifically predict exposure therapy response in specific phobia. In this double-blind randomized controlled trial, individuals with spider phobia (N = 45; female/male = 41/4) were on group basis randomly allocated to exposure therapy (n = 25; female/male = 24/1) or progressive muscle relaxation (PMR; n = 20; female/male = 17/3). Intervention effects were measured with the Fears of Spiders questionnaire. Participants also underwent a three-day fear conditioning, extinction learning, and extinction recall paradigm during functional magnetic resonance imaging at baseline. Extinction outcomes were self-reported fear and threat expectancy, and neural responses during conditioned stimulus processing and during extinction-related prediction errors (US omissions) in regions of interest (ventromedial prefrontal cortex (vmPFC) and nucleus accumbens). Results showed that exposure therapy resulted in stronger symptom reductions than PMR (Cohen's d = 0.90). Exposure therapy response was specifically predicted by prediction-error related vmPFC activation during early extinction. There were also indications vmPFC activations during conditioned safety stimulus processing at early extinction predicted therapy outcome. Neural activations during extinction recall and self-report data did however not predict therapy outcome. These findings indicate that exposure therapy may rely on neural extinction learning processes. Prediction errors are thought to drive the extinction learning process, and prediction error-related vmPFC activation specifically predicted therapy outcome. The extent to which vmPFC processes safety signals may additionally be predictive of exposure therapy response, but the specificity is less clear.

La plasticité cérébrale est régulée de façon dynamique au cours d’une vie : atteignant des sommets au cours de l’enfance, elle est réduite chez l’adulte. Toutefois, des circonstances particulières appellent à vouloir stimuler la malléabilité du cerveau adulte : pour favoriser la réhabilitation suite à un accident vasculaire cérébral ou un traumatisme crânien, pour aider l’adaptation spécifique nécessaire pour vivre avec une nouvelle prothèse ou encore pour améliorer l’efficacité de la thérapie cognitivo-comportementale suite à un traumatisme émotionnel qui a laissé un souvenir de peur qui s’est développé en syndrome de choc post-traumatique. Toutes ces situations demandent des capacités d’adaptation et une flexibilité exceptionnelles au système nerveux central. Or, pour retrouver une plasticité cérébrale telle qu’au niveau juvénile, la littérature nous apprend qu’il faut diminuer la puissance inhibitrice générée par un type d’interneurones particuliers, ceux exprimant la parvalbumine (PV+). Les fonctions des interneurones PV+ dépendent autant de leur patron de connectivité que de l’environnement extracellulaire dans lequel ils évoluent. En effet, en innervant des centaines de neurones cibles, délivrant une forte inhibition périsomatique en formant de multiples synapses autour de leur corps cellulaire et de leurs dendrites proximales, ils ont été impliqués dans l’intégration synaptique des neurones pyramidaux et dans la synchronisation des circuits corticaux. Toute manipulation ciblant cette arborescence axonale complexe pourrait s’avérer efficace à l’augmentation de la plasticité cérébrale en diminuant l’inhibition qu’elle génère. Ainsi, comprendre la signalisation moléculaire restreignant la croissance de l’arborescence axonale et la formation de boutons fonctionnels au cours de la longue phase développementale qui caractérise les interneurones PV+ aiderait à identifier des méthodes efficaces afin d’activer cette signalisation moléculaire chez l’adulte. De plus, comprendre les régulations épigénétiques liées au développement et à la maturation structurelle et fonctionnelle des interneurones PV+ offrirait une cible de choix afin de dématurer ces circuits inhibiteurs et lever un frein sur la plasticité cérébrale adulte. Nous démontrons ici que l’expression du récepteur des neurotrophines p75NTR chez les interneurones PV+ au cours de leur développement restreint la maturation de leur arborescence axonale, autant in vitro que in vivo, ainsi que l’agglomération des filets périneuronaux, autour de leur corps cellulaire. Aussi, en utilisant une version modifiée du test de ligation de proximité, nous avons résolu une controverse et démontré que le récepteur est toujours exprimé chez les interneurones PV+ du cortex adulte. Enfin, l’activation de la signalisation via p75NTR des interneurones PV+ par son ligand proBDNF est suffisante pour déstabiliser leur connectivité et restaurer la plasticité du cortex visuel suite à une privation monoculaire. Également, l’inactivation d’un régulateur épigénétique, l’histone déacétylase Hdac2, spécifiquement chez les interneurones PV+ suffit à diminuer leur connectivité efférente ainsi que l’agglomération des filets périneuronaux autour de leurs corps cellulaire tout en augmentant la rétention de l’extinction des souvenirs de peur, témoignant d’une augmentation de la plasticité cérébrale adulte. Par le séquençage d’ARNm en cellule unique, suivi de l’hybridation in situ RNAscope, nous avons identifié le gène Acan, codant pour aggrécane, une composante protéique des filets périneuronaux, comme étant exprimé de façon autonome à la cellule par les interneurones PV+ du cortex préfrontal adulte. Enfin, nous avons démontré qu’une seule injection d’un nouvel inhibiteur spécifique pour Hdac2 avant le paradigme d’extinction suffit à augmenter la rétention des souvenirs d’extinction chez l’adulte, tout en réduisant l’expression de Acan et l’agglomération des filets périneuronaux dans le cortex préfrontal. En somme, nos travaux ont montré que le remodelage des circuits des interneurones PV+ en ciblant soit le récepteur p75NTR, soit l’histone déacétylase Hdac2, peut efficacement augmenter la plasticité cérébrale chez l’adulte., Brain plasticity is dynamically regulated during a lifespan: it reaches a peak during juvenile age and decreases in adulthood. However, exceptional circumstances can drive the need to foster adult brain plasticity: to help rehabilitation after a stroke or a head trauma, to increase the adaptability of an individual facing a new life with a prosthetic, to improve the efficiency of cognitive behavioral therapy to cope with the indelible fear memory trace created by an emotional trauma. All these situations require exceptional adaptation capabilities and cognitive flexibility. Several studies have suggested that reducing inhibitory drive, in particular of a specific GABAergic interneuron population, the parvalbumin-expressing interneurons (PV+), could be an effective approach to recover juvenile brain plasticity, thereby increasing adult brain plasticity. PV+ interneuron functions depend on their axonal connectivity pattern as well as their specific extracellular environment. Indeed, by contacting hundreds of postsynaptic neurons and delivering a strong perisomatic inhibitory drive by forming multiple synapses on their somata and proximal dendrites, PV+ interneurons strongly regulate pyramidal cell synaptic integration and cortical circuit synchronisation. PV+ interneuron maturation is a prolonged process, which reaches plateau only after the end of adolescence, and correlates with the decline of developmentally regulated- brain plasticity. We hypothesize that manipulations specifically targeting PV+ interneuron highly complex axonal arborisation, and thus reducing their inhibitory drive, could be efficient tools to foster adult brain plasticity. Understanding the molecular signalling that restricts PV+ cell axonal arborisation growth and the formation of functional presynaptic boutons during their long developmental phase may help identifying efficient methods to activate this molecular pathway, thus reducing PV+ interneuron connectivity, in adults. In addition, understanding the epigenetic regulation of structural and functional maturation of PV+ interneurons may offer a choice target to dematurate these inhibitory circuits and lift a brake on adult brain plasticity. Here, we demonstrate that the expression levels of neurotrophin receptor p75NTR during PV+ interneurons development constrain the maturation of their connectivity as well as the perineuronal net agglomeration around their cell bodies in a cell-autonomous fashion, both in vitro and in vivo. Also, by using a modified version of the proximity ligand assay, we solve a long-standing debate by demonstrating p75NTR expression in PV+ interneurons in adult cortex. Finally, we show that promoting p75NTR signalisation in PV+ cortical interneurons by its ligand proBDNF is sufficient to destabilize their connectivity and restore cortical plasticity following monocular deprivation in the adult visual cortex. We further show that the deletion of the epigenetic regulator histone deacetylase 2 (Hdac2), specifically in PV+ interneurons, is sufficient to decrease their efferent connectivity and perineuronal net agglomeration around their cell bodies, while increasing fear extinction retention, a measure of brain plasticity. By single-cell RNA sequencing, followed by RNAscope in situ hybridization, we found that the Acan gene, which encodes for aggrecan, a critical perineuronal net protein component, is expressed cell-autonomously by PV+ interneurons in adult prefrontal cortex. Finally, we showed that a single injection of a novel Hdac2 specific inhibitor before extinction training is sufficient to increase fear extinction retention in adults, while reducing Acan expression and perineuronal net agglomeration in prefrontal cortex. In summary, our work shows that increasing remodeling of PV+ interneuron circuits by targeting either p75NTR receptor or histone deacetylase Hdac2 efficiently foster adult brain plasticity.

Acid sphingomyelinase (ASM) regulates a variety of physiological processes and plays an important role in emotional behavior. The role of ASM in fear-related behavior has not been investigated so far. Using transgenic mice overexpressing ASM (ASMtg) and ASM deficient mice, we studied whether ASM regulates fear learning and expression of cued and contextual fear in a classical fear conditioning paradigm, a model used to investigate specific attributes of post-traumatic stress disorder (PTSD). We show that ASM does not affect fear learning as both ASMtg and ASM deficient mice display unaltered fear conditioning when compared to wild-type littermates. However, ASM regulates the expression of contextual fear in a sex-specific manner. While ASM overexpression enhances the expression of contextual fear in both male and female mice, ASM deficiency reduces the expression of contextual fear specifically in male mice. The expression of cued fear, however, is not regulated by ASM as ASMtg and ASM deficient mice display similar tone-elicited freezing levels. This study shows that ASM modulates the expression of contextual fear but not of cued fear in a sex-specific manner and adds a novel piece of information regarding the involvement of ASM in hippocampal-dependent aversive memory.

The present study used auditory fear conditioning to assess the impact of repeated binge-like episodes of alcohol exposure during adolescence on conditioned fear in adulthood. Male and female Long-Evans rats were subjected to adolescent intermittent ethanol (AIE) exposure by vapor inhalation between post-natal day 28 and 44. After aging into adulthood, rats then underwent fear conditioning by exposure to a series of tone-shock pairings. This was followed by cued-tone extinction training, and then testing of fear recovery. In male rats, AIE exposure enhanced conditioned freezing but did not alter the time-course of extinction of cued-tone freezing. During subsequent assessment of fear recovery, AIE exposed rats exhibited less freezing during contextual fear renewal, but greater freezing during extinction recall and spontaneous recovery. Compared to males, female rats exhibited significantly lower levels of freezing during fear conditioning, more rapid extinction of freezing behavior, and significantly lower levels of freezing during the tests of fear recovery. Unlike males that were all classified as high conditioners; female rats could be parsed into either a high or low conditioning group. However, irrespective of their level of conditioned freezing, both the high and low conditioning groups of female rats exhibited rapid extinction of conditioned freezing behavior and comparatively low levels of freezing in tests of fear recovery. Regardless of group classification, AIE had no effect on freezing behavior in female rats during acquisition, extinction, or fear recovery. Lastly, exposure of male rats to the mGlu5 positive allosteric modulator CDPPB prevented AIE-induced alterations in freezing. Taken together, these observations demonstrate sex-specific changes in conditioned fear behaviors that are reversible by pharmacological interventions that target mGlu5 receptor activation.

Invited Grand Rounds talk given to the Cambridge Health Alliance Department of Psychiatry on January 12, 2022. Abstract:Childhood trauma is common, and one of the most robust and global risk factors for the development of psychopathology. When childhood trauma introduces potent threat into the environment, the way that children learn to detect, interpret, and respond to threats is altered on neurobiological and psychological levels in ways that predispose for fear- and stress-related clinical disorders. These threat learning mechanisms underlie both the etiology and common effective treatments of such disorders. Elucidating the specific ways in which childhood trauma influences these mechanisms presents an opportunity to optimize existing interventions and develop novel approaches. Learning objectives: 1.Describe three fear learning mechanisms and their role in the etiology of fear- and stress-based disorders 2.Identify how childhood trauma alters these mechanisms and thereby predisposes individuals towards psychopathology 3.Explain the relevance of fear learning mechanisms to transdiagnostic intervention processes and discuss areas ripe for optimization and innovation based on advances in work on childhood trauma

Stress represents a major risk factor for psychiatric disorders, including post-traumatic stress disorder (PTSD). Recently, we dissected the destabilizing effects of acute stress on the excitatory glutamate system in the prefrontal cortex (PFC). Here, we assessed the effects of single subanesthetic administration of ketamine (10 mg/kg) on glutamate transmission and dendritic arborization in the PFC of footshock (FS)-stressed rats, along with changes in depressive, anxious, and fear extinction behaviors. We found that ketamine, while inducing a mild increase of glutamate release in the PFC of naïve rats, blocked the acute stress-induced enhancement of glutamate release when administered 24 or 72 h before or 6 h after FS. Accordingly, the treatment with ketamine 6 h after FS also reduced the stress-dependent increase of spontaneous excitatory postsynaptic current (sEPSC) amplitude in prelimbic (PL)-PFC. At the same time, ketamine injection 6 h after FS was found to rescue apical dendritic retraction of pyramidal neurons induced by acute stress in PL-PFC and facilitated contextual fear extinction. These results show rapid effects of ketamine in animals subjected to acute FS, in line with previous studies suggesting a therapeutic action of the drug in PTSD models. Our data are consistent with a mechanism of ketamine involving re-establishment of synaptic homeostasis, through restoration of glutamate release, and structural remodeling of dendrites.

Anxiety and stress disorders are often characterized by an inability to extinguish learned fear responses. Orexins/hypocretins are involved in the modulation of aversive memories, and dysregulation of this system may contribute to the aetiology of anxiety disorders characterized by pathological fear. The mechanisms by which orexins regulate fear are unknown. Here we investigated the role of the endogenous cannabinoid system in the impaired fear extinction induced by orexin-A (OXA) in male mice. The selective inhibitor of 2-arachidonoylglycerol (2-AG) biosynthesis O7460 abolished the fear extinction deficits induced by OXA. Accordingly, increased 2-AG levels were observed in the amygdala and hippocampus of mice treated with OXA that do not extinguish fear, suggesting that high levels of this endocannabinoid are related to poor extinction. Impairment of fear extinction induced by OXA was associated with increased expression of CB2 cannabinoid receptor (CB2R) in microglial cells of the basolateral amygdala. Consistently, the intra-amygdala infusion of the CB2R antagonist AM630 completely blocked the impaired extinction promoted by OXA. Microglial and CB2R expression depletion in the amygdala with PLX5622 chow also prevented these extinction deficits. These results show that overactivation of the orexin system leads to impaired fear extinction through 2-AG and amygdalar CB2R. This novel mechanism could be of relevance for the development of novel potential approaches to treat diseases associated with inappropriate retention of fear, such as post-traumatic stress disorder, panic anxiety and phobias. This work was supported by MICINN [PID2020-116579RB-100/AEI/10.13039/501100011033] and "Ministerio de Economía y Competitividad" MINECO/FEDER, UE [SAF2017-85299-R] to FB and [PID2019-108992-RB-100] to JR, "Plan Nacional sobre Drogas" [#2019I024] to FB and “Proyectos de investigación Universidad Francisco de Vitoria [2018-2019]" to FB. M.T-B and C.I-L are supported by a predoctoral fellowship from Universidad Francisco de Vitoria. Any of the funding sources were involved in the study design and preparation. We are grateful to Dr Rosa María Tolón for her guidance on RT-PCR analyses, and Dr M. Ruth Pazos and Mario Amores for their assistance with microscopy evaluation.

Evaluation of stimulus salience is critical for any higher organism, as it allows for prioritizing of vital information, preparation of responses, and formation of valuable memory. The paraventricular nucleus of the thalamus (PVT) has recently been identified as an integrator of stimulus salience but the neurochemical basis and afferent input regarding salience signaling have remained elusive. Here we report that neuropeptide S (NPS) signaling in the PVT is necessary for stimulus salience encoding, including aversive, neutral and reinforcing sensory input. Taking advantage of a striking deficit of both NPS receptor (NPSR1) and NPS precursor knockout mice in fear extinction or novel object memory formation, we demonstrate that intra-PVT injections of NPS can rescue the phenotype in NPS precursor knockout mice by increasing the salience of otherwise low-intensity stimuli, while intra-PVT injections of NPSR1 antagonist in wild type mice partially replicates the knockout phenotype. The PVT appears to provide stimulus salience encoding in a dose- and NPS-dependent manner. PVT NPSR1 neurons recruit the nucleus accumbens shell and structures in the prefrontal cortex and amygdala, which were previously linked to the brain salience network. Overall, these results demonstrate that stimulus salience encoding is critically associated with NPS activity in the PVT.

Reproductive experience leads to long-lasting changes in anxiety-like behaviour and fear extinction, the laboratory model of exposure therapy for anxiety disorders. For example, fear extinction is influenced by estrous cycle in nulliparous (no reproductive experience) female rats, but this effect is abolished in primiparous (one reproductive experience) females. It is unclear whether such changes are driven by pregnancy, maternal experience of caring for offspring during the postpartum period, or a combination of both experiences. The present study sought to determine the influence of maternal experience (i.e., exposure to pups and mother-pup interactions) on fear extinction in primiparous rats. In Experiment 1, we tested whether pup exposure is necessary to mitigate estrous effects on fear extinction in primiparous rats. Age-matched nulliparous rats, primiparous rats, and primiparous rats who experienced pregnancy but not pup exposure, underwent fear conditioning on day 1 (2 months post-parturition), extinction training during proestrus (high sex hormones) or metestrus (low sex hormones) on day 2, and extinction recall on day 3. Replicating past research, nulliparous rats showed impaired extinction recall when they were extinguished during metestrus compared to proestrus. In contrast, primiparous rats with and without pup exposure showed comparable extinction recall irrespective of estrous phase. In Experiment 2, we assessed whether naturally-occurring variation in mother-pup interactions predict future fear extinction performance and anxiety-like behaviour. During the first week of lactation, primiparous rats were measured for maternal behaviours toward pups. Primiparous rats were then tested on the light-dark box and elevated plus maze to measure anxiety-like behaviour and underwent a fear extinction protocol 1 month post-weaning. We found no significant correlations between maternal behaviour and fear extinction outcomes or anxiety-like behaviour. Our findings suggest that pregnancy, not maternal experience, mitigates the impact of estrous cycle on fear extinction. In addition, natural variation in maternal experience does not appear to contribute to variability in future fear extinction outcomes or anxiety-like behaviour in primiparous rats.

The ability to extinguish aversive memories when they are no longer associated with danger is critical for balancing survival with competing adaptive demands. Previous studies demonstrated that the infralimbic cortex (IL) is essential for extinction of learned fear, while neural activity in the prelimbic cortex (PL) facilitates fear responding and is negatively correlated with the strength of extinction memories. Though these adjacent regions in the prefrontal cortex maintain mutual synaptic connectivity, it has been unclear whether PL and IL interact functionally with each other during fear extinction learning. Here we addressed this question by recording local field potentials (LFPs) simultaneously from PL and IL of awake behaving rats during extinction of auditory fear memories. We found that LFP power in the fast gamma frequency (100–200 Hz) in both PL and IL regions increased during extinction learning. In addition, coherency analysis showed that synchronization between PL and IL in the fast gamma frequency was enhanced over the course of extinction. These findings support the hypothesis that interregional interactions between PL and IL increase as animals extinguish aversive memories. Supplementary Information The online version contains supplementary material available at 10.1186/s13041-021-00884-6.

Fear conditioning describes a learning mechanism during which a specific stimulus gets associated with an aversive event (i.e., an unconditioned stimulus; US). Thereby, this initially neutral or arbitrary stimulus becomes a so-called “conditioned” stimulus (CS), which elicits a conditioned threat response. Fear extinction refers to the decrease in conditioned threat responses as soon as the CS is repeatedly presented in the absence of the US. While fear conditioning is an important learning model for understanding the etiology and maintenance of anxiety and fear-related disorders, extinction learning is considered to reflect the most important learning process of exposure therapy. Neurophysiological signatures of fear conditioning have been widely studied in rodents, leading to the development of groundbreaking neurobiological models, including brain regions such as the amygdala, insula, and prefrontal areas. These models aim to explain neural mechanisms of threat processing, with the ultimate goal to improve treatment strategies for pathological fear. Recording intracranial electrical activity of single units in animals offers the opportunity to uncover neural processes involved in threat processing with excellent spatial and temporal resolution. A large body of functional magnetic resonance imaging (fMRI) studies have helped to translate this knowledge about the anatomy of fear conditioning into the human realm. fMRI is an imaging technique with a high spatial resolution that is well suited to study slower brain processes. However, the temporal resolution of fMRI is relatively poor. By contrast, electroencephalography (EEG) is a neuroscientific method to capture fast and transient cortical processes. While EEG offers promising opportunities to unravel the speed of neural threat processing, it also provides the possibility to study oscillatory brain activity (e.g., prefrontal theta oscillations). The present thesis contains six research manuscripts, describing fear conditioning studies that mainly applied EEG methods in combination with other central (fMRI) and peripheral (skin conductance, heart rate, and fear-potentiated startle) measures. A special focus of this thesis lies in methodological considerations for EEG fear conditioning research. In addition, catecholaminergic mechanisms are studied, with the ultimate goal of opening up new translational perspectives. Taken together, the present thesis addresses several methodological challenges for neuroscientific (in particular, EEG) fear conditioning research (e.g., appropriate US types and experimental designs, signal-to-noise ratio, simultaneous EEG-fMRI). Furthermore, this thesis gives critical insight into catecholaminergic (noradrenaline and dopamine) mechanisms. A variety of neuroscientific methods (e.g., EEG, fMRI, peripheral physiology, pharmacological manipulation, genetic associations) have been combined, an approach that allowed us (a) to translate knowledge from animal studies to human research, and (b) to stimulate novel clinical directions., Furchtkonditionierung beschreibt einen Lernmechanismus, bei dem ein spezifischer Reiz mit einem aversiven Ereignis (d.h. einem unkonditionierten Reiz; US) assoziiert wird. Dadurch wird dieser zunächst neutrale oder beliebig ausgewählte Reiz zu einem sogenannten „konditionierten“ Reiz (CS), der eine konditionierte Bedrohungs-Reaktion hervorruft. Unter Furchtextinktion versteht man die Abnahme der konditionierten Bedrohungs-Reaktion, sobald der CS wiederholt in Abwesenheit des US präsentiert wird. Während die Furchtkonditionierung ein wichtiges Lernmodell für das Verständnis der Ätiologie und Aufrechterhaltung von Angststörungen und Furcht-assoziierten Störungen darstellt, wird das Extinktionslernen als der wichtigste Lernprozess bei der Expositionstherapie angesehen. Neurophysiologische Korrelate der Furchtkonditionierung wurden umfassend in Nagetieren untersucht, was zur Entwicklung wegweisender neurobiologischer Modelle führte, welche Gehirnregionen wie die Amygdala, die Insula und präfrontale Areale beinhalten. Diese Modelle zielen darauf ab, neuronale Mechanismen der Bedrohungs-Verarbeitung zu erklären, mit dem letztendlichen Ziel, Behandlungs-Strategien für pathologische Furcht zu verbessern. Die Aufzeichnung der intrakraniellen elektrischen Aktivität einzelner Nervenzellen bietet im Tiermodell die Möglichkeit, neuronale Prozesse, die an der Bedrohungs-Verarbeitung beteiligt sind, mit hervorragender räumlicher und zeitlicher Auflösung aufzudecken. Eine große Anzahl von Studien mittels funktioneller Magnetresonanztomographie (fMRT) hat dazu beigetragen, dieses Wissen über anatomische Grundlagen der Furchtkonditionierung auf den Menschen zu übertragen. fMRT ist ein bildgebendes Verfahren mit hoher räumlicher Auflösung, das sich gut für die Untersuchung langsamerer Gehirnprozesse eignet. Allerdings ist die zeitliche Auflösung der fMRT relativ niedrig. Im Gegensatz dazu ist die Elektroenzephalographie (EEG) eine neurowissenschaftliche Methode, die sich hervorragend zur Erfassung schneller und transienter kortikaler Prozesse eignet. Während die EEG-Methodik vielversprechende Möglichkeiten eröffnet, die Geschwindigkeit neuronaler Bedrohungs-Verarbeitung zu entschlüsseln, bietet sie auch die Möglichkeit, oszillatorische Hirnaktivität (z. B. präfrontale Theta-Oszillationen) zu untersuchen. Die vorliegende Dissertation enthält sechs Forschungs-Manuskripte und beschreibt Studien zur Furchtkonditionierung, bei denen hauptsächlich EEG-Methoden in Kombination mit anderen zentral- (fMRT) und peripher-physiologischen Methoden (elektrodermale Aktivität, Herzfrequenz und Modulation des Schreckreflexes) eingesetzt wurden. Ein besonderer Schwerpunkt dieser Arbeit liegt auf methodischen Überlegungen zur Furchtkonditionierungs-Forschung mit EEG. Außerdem werden katecholaminerge Mechanismen untersucht, mit dem langfristigen Ziel, neue translationale Perspektiven zu eröffnen. Insgesamt adressiert die vorliegende Dissertation mehrere methodische Herausforderungen für die neurowissenschaftliche (insbesondere EEG) Furchtkonditionierungs-Forschung (z. B. geeignete US-Typen und experimentelle Paradigmen, Signal-Rausch-Verhältnis, simultane EEG-fMRT). Darüber hinaus gibt diese Arbeit wichtige Einblicke in katecholaminerge (Noradrenalin und Dopamin) Mechanismen. Eine Vielzahl neurowissenschaftlicher Methoden (z. B. EEG, fMRT, peripher-physiologische Maße, pharmakologische Manipulation, genetische Assoziationen) wurde kombiniert. Dieser Ansatz ermöglichte es uns, (a) Erkenntnisse aus Tiermodellen in die Humanforschung zu übertragen und (b) neue klinische Perspektiven aufzuzeigen.

Several psychiatric conditions such as phobias, generalized anxiety, and post-traumatic stress disorder (PTSD) are characterized by pathological fear and anxiety. The main therapeutic approach used in the management of these disorders is exposure-based therapy, which is conceptually based upon fear extinction with the formation of a new safe memory association, allowing the reduction in behavioral conditioned fear responses. Nevertheless, this approach is only partially resolutive, since many patients have difficulty following the demanding and long process, and relapses are frequently observed over time. One strategy to improve the efficacy of the cognitive therapy is the combination with pharmacological agents. Therefore, the identification of compounds able to strengthen the formation and persistence of the inhibitory associations is a key goal. Recently, growing interest has been aroused by the neuropeptide oxytocin (OXT), which has been shown to have anxiolytic effects. Furthermore, OXT receptors and binding sites have been found in the critical brain structures involved in fear extinction. In this review, the recent literature addressing the complex effects of OXT on fear extinction at preclinical and clinical levels is discussed. These studies suggest that the OXT roles in fear behavior are due to its local effects in several brain regions, most notably, distinct amygdaloid regions.

Reminders of loved ones have long been avoided during extinction-based treatments because of their assumed status as safety signals, which, by inhibiting fear in the moment, impair the long-term outcomes of fear extinction. Yet, recent work has demonstrated that in contrast to standard safety signals, social support reminders actually enhance fear extinction and lead to lasting reduction of fear, suggesting that they may have beneficial effects during exposure therapy that have before-now been overlooked. Here, we argue for a revision of the assumption that social support is detrimental to fear extinction processes and propose that future work should focus on the potential of social support reminders to improve treatment outcomes in those with anxiety disorders.

Perineuronal nets (PNNs) have an important physiological role in the retention of learning by restricting cognitive flexibility. Their deposition peaks after developmental periods of intensive learning, usually in late childhood, and they help in long-term preservation of newly acquired skills and information. Modulation of PNN function by various techniques enhances plasticity and regulates the retention of memories, which may be beneficial when memory persistence entails negative symptoms such as post-traumatic stress disorder (PTSD). In this study, we investigated the role of PTP sigma [receptor-type tyrosine-protein phosphatase S, a phosphatase that is activated by binding of chondroitin sulfate proteoglycans (CSPGs) from PNNs] in retention of memories using Novel Object Recognition and Fear Conditioning models. We observed that mice haploinsufficient for PTPRS gene (PTP sigma(+/-)), although having improved short-term object recognition memory, display impaired long-term memory in both Novel Object Recognition and Fear Conditioning paradigm, as compared to WT littermates. However, PTP sigma(+/-) mice did not show any differences in behavioral tests that do not heavily rely on cognitive flexibility, such as Elevated Plus Maze, Open Field, Marble Burying, and Forced Swimming Test. Since PTP sigma has been shown to interact with and dephosphorylate TRKB, we investigated activation of this receptor and its downstream pathways in limbic areas known to be associated with memory. We found that phosphorylation of TRKB and PLC gamma are increased in the hippocampus, prefrontal cortex, and amygdaloid complex of PTP sigma(+/-) mice, but other TRKB-mediated signaling pathways are not affected. Our data suggest that PTP sigma downregulation promotes TRKB phosphorylation in different brain areas, improves short-term memory performance but disrupts long-term memory retention in the tested animal models. Inhibition of PTP sigma or disruption of PNN-PTP sigma-TRKB complex might be a potential target for disorders where negative modulation of the acquired memories can be beneficial.

The inability to extinguish a traumatic memory is a key aspect of post-traumatic stress disorder (PTSD). While PTSD affects 10–20% of individuals who experience a trauma, women are particularly susceptible to developing the disorder. Despite this notable female vulnerability, few studies have investigated this particular resistance to fear extinction observed in females. Similar to humans, rodent models of Pavlovian fear learning and extinction show a wide range of individual differences in fear learning and extinction, although female rodents are considerably understudied. Therefore, the present study examined individual differences in fear responses, including freezing behavior and ultrasonic vocalizations (USVs), of female Long–Evans rats during acquisition of fear conditioning and cued fear extinction. Similar to prior studies in males, female rats displayed individual variation in freezing during cued fear extinction and were divided into extinction competent (EC) and extinction resistant (ER) phenotypes. Differences in freezing between ER and EC females were accompanied by shifts in rearing during extinction, but no darting was seen in any trial. Freezing behavior during fear learning did not differ between the EC and ER females. Vocalizations emitted in the 22 and 50 kHz ranges during fear learning and extinction were also examined. Unlike vocalizations seen in previous studies in males, very few 22 kHz distress vocalizations were emitted by female rats during fear acquisition and extinction, with no difference between ER and EC groups. Interestingly, all female rats produced significant levels of 50 kHz USVs, and EC females emitted significantly more 50 kHz USVs than ER rats. This difference in 50 kHz USVs was most apparent during initial exposure to the testing environment. These results suggest that like males, female rodents show individual differences in both freezing and USVs during fear extinction, although females appear to vocalize more in the 50 kHz range, especially during initial periods of exposure to the testing environment, and emit very few of the 22 kHz distress calls that are typically observed in males during fear learning or extinction paradigms. Overall, these findings show that female rodents display fear behavior repertoires divergent from males.

This study investigated whether transcutaneous auricular vagus nerve stimulation (taVNS) enhances reversal learning and augments noradrenergic biomarkers (i.e., pupil size, cortisol, and salivary alpha-amylase [sAA]). We also explored the effect of taVNS on respiratory rate and cardiac vagal activity (CVA). Seventy-one participants received stimulation of either the cymba concha (taVNS) or the earlobe (sham) of the left ear. After learning a series of cue-outcome associations, the stimulation was applied before and throughout a reversal phase in which cue-outcome associations were changed for some (reversal), but not for other (distractor) cues. Tonic pupil size, salivary cortisol, sAA, respiratory rate, and CVA were assessed at different time points. Contrary to our hypothesis, taVNS was not associated with an overall improvement in performance on the reversal task. Compared to sham, the taVNS group performed worse for distractor than reversal cues. taVNS did not increase tonic pupil size and sAA. Only post hoc analyses indicated that the cortisol decline was steeper in the sham compared to the taVNS group. Exploratory analyses showed that taVNS decreased respiratory rate but did not affect CVA. The weak and unexpected effects found in this study might relate to the lack of parameters optimization for taVNS and invite to further investigate the effect of taVNS on cortisol and respiratory rate. ispartof: Psychophysiology vol:58 issue:10 pages:1-20 ispartof: location:United States status: published

Cognitive behavioral therapy (CBT) including exposure and response prevention is a well-established treatment for obsessive-compulsive disorder (OCD) and is based on the principles of fear extinction. Fear extinction is linked to structural and functional variability in the ventromedial prefrontal cortex (vmPFC) and has been consistently associated with glutamate neurotransmission. The relationship between vmPFC glutamate and fear extinction and its effects on CBT outcome have not yet been explored in adults with OCD. We assessed glutamate levels in the vmPFC using 3T magnetic resonance spectroscopy, and fear extinction (learning and recall) using skin conductance responses during a 2-day experimental paradigm in OCD patients (n = 17) and in healthy controls (HC; n = 13). Obsessive-compulsive patients (n = 12) then received manualized CBT. Glutamate in the vmPFC was negatively associated with fear extinction recall and positively associated with CBT outcome (with higher glutamate levels predicting a better outcome) in OCD patients. Glutamate levels in the vmPFC in OCD patients were not significantly different from those in HC, and were not associated with OCD severity. Our results suggest that glutamate in the vmPFC is associated with fear extinction recall and CBT outcome in adult OCD patients.

Background: Exposure is the gold standard treatment for phobic anxiety and is thought to represent the clinical application of extinction learning. Reward sensitivity might however also represent a predictive factor for exposure therapy outcome, as this therapy promotes positive experiences and involves positive comments by the therapist. We hypothesized that high reward sensitivity, as expressed by elevated reward expectancy and reward value, can be associated with better outcome to exposure therapy specifically.Methods: Forty-four participants with a specific phobia for spiders were included in the current study. Participants were randomly assigned to exposure therapy (n = 25) or progressive muscle relaxation (PMR) (n = 19). Treatment outcome was defined as pre- versus post-therapy phobia symptoms. Before treatment, functional brain responses and behavioral responses (i.e. reaction time and accuracy) during reward anticipation and consumption were assessed with the Monetary Incentive Delay task (MID). Behavioral and neural responses in regions of interest (i.e. nucleus accumbens, ventromedial prefrontal cortex and the ventral tegmental area) as well as across the whole-brain were subsequently regressed on treatment outcomes.Results: Exposure therapy was more effective in reducing phobia symptoms than PMR. Longer reaction times to reward cues and lower activation in the left posterior cingulate cortex during reward consumption were selectively associated with symptoms reductions following exposure therapy but not following PMR. Only within the exposure therapy group, greater symptom reduction was related to increased activation in the ventrolateral prefrontal cortex during reward anticipation, and decreased activation in the medial prefrontal cortex during reward consumption.Conclusion: Results indicate that individual differences in reward sensitivity can specifically predict exposure therapy outcome. Although activation in regions of interest were not related to therapy outcome, regions involved in attentional processing of reward cues were predictive of phobic symptom change following exposure therapy but not PMR.

Background: Exposure is the gold standard treatment for phobic anxiety and is thought to represent the clinical application of extinction learning. Reward sensitivity might however also represent a predictive factor for exposure therapy outcome, as this therapy promotes positive experiences and involves positive comments by the therapist. We hypothesized that high reward sensitivity, as expressed by elevated reward expectancy and reward value, can be associated with better outcome to exposure therapy specifically.Methods: Forty-four participants with a specific phobia for spiders were included in the current study. Participants were randomly assigned to exposure therapy (n = 25) or progressive muscle relaxation (PMR) (n = 19). Treatment outcome was defined as pre- versus post-therapy phobia symptoms. Before treatment, functional brain responses and behavioral responses (i.e. reaction time and accuracy) during reward anticipation and consumption were assessed with the Monetary Incentive Delay task (MID). Behavioral and neural responses in regions of interest (i.e. nucleus accumbens, ventromedial prefrontal cortex and the ventral tegmental area) as well as across the whole-brain were subsequently regressed on treatment outcomes.Results: Exposure therapy was more effective in reducing phobia symptoms than PMR. Longer reaction times to reward cues and lower activation in the left posterior cingulate cortex during reward consumption were selectively associated with symptoms reductions following exposure therapy but not following PMR. Only within the exposure therapy group, greater symptom reduction was related to increased activation in the ventrolateral prefrontal cortex during reward anticipation, and decreased activation in the medial prefrontal cortex during reward consumption.Conclusion: Results indicate that individual differences in reward sensitivity can specifically predict exposure therapy outcome. Although activation in regions of interest were not related to therapy outcome, regions involved in attentional processing of reward cues were predictive of phobic symptom change following exposure therapy but not PMR.

This study investigated the effect of exogenously administered polyphenolic antioxidant, α-glycosyl isoquercitrin (AGIQ), on neural function in rats following dietary exposure at 0.5% from gestational day 6 to postnatal day 77, in comparison with nonpolyphenolic α-lipoic acid (ALA) at 0.2%. AGIQ-exposed offspring revealed enhanced fear extinction learning at the 3rd trial and transcript upregulation of Fos and Kif21b in the hippocampal dentate gyrus and Grin2d in the amygdala. AGIQ also increased the number of FOS-immunoreactive (+) hippocampal granule cells. While ALA showed fear extinction learning-related transcript expression changes, it changed neither fear extinction learning nor FOS+ cell numbers. The increases of FOS+ cells and Grin2d transcripts by AGIQ suggested an association with increase of synaptic plasticity, leading to enhancement of fear extinction learning. AGIQ may also upregulate KIF21B, a recently identified memory-rewriting molecule. The present study findings suggest a possible therapeutic use of AGIQ in mitigating some stress disorders.

The benefits of exposure-based interventions for anxiety disorders are substantial but not stable for everyone, given that these interventions are often followed by relapse of symptoms. A body of research provides a background on how to add certain strategies in exposure-based therapy to prevent relapse in anxiety disorders. This review summarizes some of these strategies and provides clear-cut clinical implications. Studies that provide support for two types of strategies to prevent relapse have been reviewed—the use of multiple contexts and the use of retrieval cues. The use of multiple contexts reduces context and stimulus specificity of extinction learning during exposure, while the use of retrieval cues enhances memory (re)consolidation and retrieval after exposure. The described strategies to enhance the accessibility and therefore the retrievability of exposure-based learning to prevent relapse in anxiety disorders can be summarized as advice to conduct exposure under variable conditions. This way, the generalizability of what is learned during exposure to the patients’ daily life after treatment improves. Therefore, adding these strategies in the course of exposure-based treatment of anxiety disorders seems beneficial. However, future replications and translational studies are needed to verify ecological validity.

Disproportionate, maladapted, and generalized fear are essential hallmarks of posttraumatic stress disorder (PTSD), which develops upon severe trauma in a subset of exposed individuals. Among the brain areas that are processing fear memories, the hippocampal formation exerts a central role linking emotional-affective with cognitive aspects. In the hippocampus, neuronal excitability is constrained by multiple GABAergic interneurons with highly specialized functions and an extensive repertoire of co-released neuromodulators. Neuropeptide Y (NPY) is one of these co-transmitters that significantly affects hippocampal signaling, with ample evidence supporting its fundamental role in emotional, cognitive, and metabolic circuitries. Here we investigated the role of NPY in relation to GABA, both released from the same interneurons of the dorsal dentate gyrus (DG), in different aspects of fear conditioning. We demonstrated that activation of dentate GABA neurons specifically during fear recall reduced cue-related as well as trace-related freezing behavior, whereas inhibition of the same neurons had no significant effects. Interestingly, concomitant overexpression of NPY in these neurons did not further modify fear recall, neither under baseline conditions nor upon chemogenetic stimulation. However, potentially increased co-release of NPY substantially reduced contextual fear, promoted extinction learning, and long-term suppression of fear in a foreground context–conditioning paradigm. Importantly, NPY in the dorsal DG was not only expressed in somatostatin neurons, but also in parvalbumin-positive basket cells and axoaxonic cells, indicating intense feedback and feedforward modulation of hippocampal signaling and precise curtailing of neuronal engrams. Thus, these findings suggest that co-release of NPY from specific interneuron populations of the dorsal DG modifies dedicated aspects of hippocampal processing by sharpening the activation of neural engrams and the consecutive fear response. Since inappropriate and generalized fear is the major impediment in the treatment of PTSD patients, the dentate NPY system may be a suitable access point to ameliorate PTSD symptoms and improve the inherent disease course.

Anxiety disorders are among the most prevalent mental disorders. Present treatments such as cognitive behavior therapy and pharmacological treatments show only moderate success, which emphasizes the importance for the development of new treatment protocols. Non-invasive brain stimulation methods such as repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) have been probed as therapeutic option for anxiety disorders in recent years. Mechanistic information about their mode of action, and most efficient protocols is however limited. Here the fear extinction model can serve as a model of exposure therapies for studying therapeutic mechanisms, and development of appropriate intervention protocols. We systematically reviewed 30 research articles that investigated the impact of rTMS and tDCS on fear memory and extinction in animal models and humans, in clinical and healthy populations. The results of these studies suggest that tDCS and rTMS can be efficient methods to modulate fear memory and extinction. Furthermore, excitability-enhancing stimulation applied over the vmPFC showed the strongest potential to enhance fear extinction. We further discuss factors that determine the efficacy of rTMS and tDCS in the context of the fear extinction model and provide future directions to optimize parameters and protocols of stimulation for research and treatment.

Recent meta-analyses indicated differences in fear acquisition and extinction between patients with anxiety-related disorders and comparison subjects. However, these effects are small and may hold for only a subsample of patients. To investigate individual trajectories in fear acquisition and extinction across patients with anxiety-related disorders (N = 104; before treatment) and comparison subjects (N = 93), data from a previous study (Duits et al., 2017) were re-analyzed using data-driven latent class growth analyses. In this explorative study, subjective fear ratings, shock expectancy ratings and startle responses were used as outcome measures. Fear and expectancy ratings, but not startle data, yielded distinct fear conditioning trajectories across participants. Patients were, compared to controls, overrepresented in two distinct dysfunctional fear conditioning trajectories: impaired safety learning and poor fear extinction to danger cues. The profiling of individual patterns allowed to determine that whereas a subset of patients showed trajectories of dysfunctional fear conditioning, a significant proportion of patients (≥50 %) did not. The strength of trajectory analyses as opposed to group analyses is that it allows the identification of individuals with dysfunctional fear conditioning. Results suggested that dysfunctional fear learning may also be associated with poor treatment outcome, but further research in larger samples is needed to address this question.

Recent meta-analyses indicated differences in fear acquisition and extinction between patients with anxiety related disorders and comparison subjects. However, these effects are small and may hold for only a subsample of patients. To investigate individual trajectories in fear acquisition and extinction across patients with anxiety-related disorders (N = 104; before treatment) and comparison subjects (N = 93), data from a previous study (Duits et al., 2017) were re-analyzed using data-driven latent class growth analyses. In this explorative study, subjective fear ratings, shock expectancy ratings and startle responses were used as outcome measures. Fear and expectancy ratings, but not startle data, yielded distinct fear conditioning trajectories across participants. Patients were, compared to controls, overrepresented in two distinct dysfunctional fear conditioning trajectories: impaired safety learning and poor fear extinction to danger cues. The profiling of individual patterns allowed to determine that whereas a subset of patients showed trajectories of dysfunctional fear conditioning, a significant proportion of patients (?50 %) did not. The strength of trajectory analyses as opposed to group analyses is that it allows the identification of individuals with dysfunctional fear conditioning. Results suggested that dysfunctional fear learning may also be associated with poor treatment outcome, but further research in larger samples is needed to address this question.

The ability to extinguish fear memories when threats are no longer present is critical for adaptive behavior. Fear extinction represents a new learning process that eventually leads to the formation of extinction memories. Understanding the neural basis of fear extinction has considerable clinical significance as deficits in extinction learning are the hallmark of human anxiety disorders. In recent years, the dopamine (DA) system has emerged as one of the key regulators of fear extinction. In this review article, we highlight recent advances that have demonstrated the crucial role DA plays in mediating different phases of fear extinction. Emerging concepts and outstanding questions for future research are also discussed.

Fear renewal occurs when the context changes after fear extinction; however, whether avoidance is also influenced by context changes following fear extinction is untested. Forty-two participants performed an avoidance task within a typical fear renewal procedure. During Pavlovian conditioning, two stimuli (CS+) were associated with an aversive electrical stimulus (US), while a third stimulus was not (CS-). During subsequent avoidance learning, clicking a button canceled the delivery of the US during one but not the other CS+. Fear-related levels were then reduced by removing the US and the button in a new context (fear extinction with response prevention [Ext-RP]). Next, persistence of avoidance was tested in the extinction context B (group ABB) or the original conditioning context A (group ABA). We also tested whether ratings of relief pleasantness (based on both the CS- and the avoided CS+) during avoidance and Ext-RP predicted individual levels of persistent avoidance. Results showed that persistent avoidance was higher in conditioning context A than in extinction context B, and was predicted by higher relief pleasantness during avoidance conditioning. We conclude that persistent avoidance poses a threat to the long-term success of Ext-RP, and we propose that interventions aimed at mitigating the influence of context and relief levels might prove beneficial in this regard. ispartof: BEHAVIOUR RESEARCH AND THERAPY vol:138 ispartof: location:England status: published

Recent neurobiological models of obsessive-compulsive disorder (OCD) have highlighted the potential role of abnormalities in fear learning processes. We compared brain activation -as assessed with whole-brain functional magnetic resonance imaging- during fear conditioning, fear extinction learning, and fear extinction recall in patients with OCD (n = 18) and healthy controls (n = 18). We also investigated whether brain activation during any of these processes was associated with exposure-based cognitive-behavioral therapy (CBT) outcome in patients. Patients with OCD showed significantly lower brain activation in the right insulo-opercular region and the dorsal anterior cingulate cortex during fear conditioning in comparison to healthy controls. Moreover, brain activation in the right insula predicted CBT outcome, with lower activation predicting a better outcome. Brain activation during extinction learning or recall did not differ between patients and controls or predicted CBT outcome in patients. Our results suggest that neural activations during fear conditioning in patients with OCD are abnormal and predict CBT outcome.

Insomnia is one of the most common health issues, with occasional symptoms affecting up to 50% of the general population. Lack of sleep is associated with many negative health effects. A new evolutionary hypothesis has been proposed to explain the mechanism behind insomnia symptoms. The evolutionary-emotional hypothesis proposes that while acute insomnia might be advantageous from an evolutionary perspective, chronic insomnia is maladaptive and may follow from a failure or delay of fear extinction. The aim of the current thesis was to investigate which neural mechanisms might be at work if one is to consider the evolutionaryemotional hypothesis about the causes of insomnia plausible and to review studies from cognitive neuroscience to discover what support there might be for the hypothesis. Studies have found heightened activation in fear-related brain areas in insomnia patients. Delayed fear extinction and altered emotion regulation circuitry, among other things, were also observed for insomnia patients. However, few experimental studies on the effect of fear extinction on sleep in insomnia patients have been conducted. At this time, some emerging evidence lends support for the evolutionary-emotional hypothesis of insomnia, but more studies that directly assess fear conditioning and fear extinction processes in insomnia patients are needed to assess the explanatory power of the theory.