D-Cycloserine Augmentation of Exposure-Based Cognitive Behavior Therapy for Anxiety, Obsessive-Compulsive, and Posttraumatic Stress Disorders: A Systematic Review and Meta-analysis of Individual Participant Data

Effects of sodium benzoate on cognitive function in neuropsychiatric disorders: a systematic review and meta-analysis

We performed a systematic review and meta-analysis on sodium benzoate's effects on cognitive function and other psychiatric symptoms in individuals with neuropsychiatric disorders. We searched PubMed, Embase, Cochrane Library, and PsychInfo databases until September 2023. A random-effects meta-analysis was performed within a frequentist framework. To investigate the potential sources of heterogeneity, we performed subgroup analyses based on sex, dose, diagnosis, and risk of bias of the included studies. Trial sequential analyses were performed to investigate the statistical power of the synthesized studies. The certainty in evidence was evaluated using the Grading of Recommendations Assessment, Development and Evaluation approach. A total of 10 studies were included in the analysis. Sodium benzoate demonstrated a small-to-moderate positive effect on global cognitive function compared with placebo (standardized mean difference 0.40, 95% confidence interval 0.20 to 0.60, high certainty). Subgroup analyses suggested more pronounced effects in women; individuals receiving doses >500 mg/day; and individuals with early-phase Alzheimer's disease, chronic schizophrenia, or major depressive disorder. Sodium benzoate also demonstrated potential efficacy in enhancing the speed of processing, working memory, verbal learning and memory, visual learning and memory, and reasoning and problem solving. Furthermore, sodium benzoate was effective for positive psychotic symptoms but not for negative psychotic and depressive symptoms with moderate certainty. The current evidence strongly supports the positive effects of sodium benzoate on cognitive function in neuropsychiatric disorders. Further research is required to confirm its efficacy across different subtypes or stages of neurocognitive disorders and within specific cognitive domains.

Systematic Review Registration

PROSPERO, identifier CRD42023457462.

Ketamine-enhanced prolonged exposure therapy in veterans with PTSD: A randomized controlled trial protocol

BACKGROUND

The 2023 VA/DoD Clinical Practice Guideline for the Management of PTSD recommends individual, manualized trauma-focused such as Prolonged Exposure (PE) over pharmacologic interventions for the primary treatment of PTSD. Unfortunately, clinical trials of trauma-based therapies in the military and veteran population showed that 30% to 50% of patients did not demonstrate clinically meaningful symptom change. Ketamine, an FDA-approved anesthetic with potent non-competitive glutamatergic N-methyl-d-aspartate antagonistic properties, has demonstrated to enhance the recall of extinction learning and decrease fear renewal without interference of extinction training in preclinical studies.

METHODS

We plan to conduct a single site RCT comparing three ketamine treatment vs. active placebo (midazolam) adjunct to PE therapy among Veterans with PTSD. Pharmacological phase will start simultaneously with PE session 1. Infusions will be administered 24 h. prior to PE session for the first 3 weeks. After PE is completed (session 10), patients will be assessed during a 3-month follow-up period at various time points. We estimate that out of 100 veterans, 80 will reach time point for primary outcome measure and will be considered for primary analysis. Secondary outcomes include severity of depression and anxiety scores, safety and tolerability of ketamine-enhanced PE therapy, cognitive performance during treatment and early improvement during PE related to the rate of dropouts during PE therapy.

DISCUSSION

Results of the proposed RCT could provide scientific foundation to distinguish the essential components of this approach, enhance the methodology, elucidate the mechanisms involved, and identify sub-PTSD populations that most likely benefit from this intervention.

Combined effects of pharmacological interventions and intermittent theta-burst stimulation on motor sequence learning

Drugs that modulate N-methyl-D-aspartate (NMDA) or γ-Aminobutyric acid type A (GABA A ) receptors can shed light on their role in synaptic plasticity mechanisms underlying the effects of non-invasive brain stimulation. However, research on the combined effects of these drugs and exogenous stimulation on motor learning is limited. This study aimed to investigate the effects of pharmacological interventions combined with intermittent theta-burst stimulation (iTBS) on human motor learning. Nine right-handed healthy subjects (mean age ± SD: 31.56 ± 12.96 years; 6 females) participated in this double-blind crossover study. All participants were assigned to four drug conditions in a randomized order: (1) D-cycloserine (partial NMDA receptor agonist), (2) D-cycloserine + dextromethorphan (NMDA receptor agonist + antagonist), (3) lorazepam (GABA A receptor agonist), and (4) placebo (identical microcrystalline cellulose capsule). After drug intake, participants practiced the 12-item keyboard sequential task as a baseline measure. Two hours after drug intake, iTBS was administered at the primary motor cortex. Following iTBS, the retention test was performed in the same manner as the baseline measure. Our findings revealed that lorazepam combined with iTBS impaired motor learning during the retention test. Future studies are still needed for a better understanding of the mechanisms through which TMS may influence human motor learning.

Treatment Approaches for Posttraumatic Stress Disorder Derived From Basic Research on Fear Extinction

This brief review article will describe treatment approaches for posttraumatic stress disorder (PTSD) based on findings from basic research. The focus of this review will be fear conditioning and extinction models, which provide a translational model of PTSD that can help translate basic research in nonhuman animals through well-controlled trials confirming the efficacy of treatment approaches in humans with PTSD such as prolonged exposure therapy. Specific cognitive aspects of fear extinction processes, including consolidation and reconsolidation, are reviewed along with behavioral and pharmacological treatment strategies based on basic research in these areas including attempts to prevent the development of PTSD as well as the treatment of chronic PTSD. Pharmacological, behavioral, and device-based augmentation strategies of PTSD treatment based in basic science findings are reviewed, including those that disrupt noradrenergic receptor processes, medications that act on NMDA receptors, physical exercise, cannabinoids, estradiol, dexamethasone, yohimbine, losartan, dopamine, and MDMA, along with the evidence for their efficacy in human clinical samples. While fear extinction provides an exciting translational opportunity to improve PTSD based on basic science findings, we review limitations and challenges of the extant literature as well as future directions.

Pediatric Treatment-Resistant Obsessive Compulsive Disorder: Treatment Options and Challenges

Pediatric obsessive-compulsive disorder (OCD) is a chronic, potentially debilitating psychiatric condition. Although effective treatments exist, at least 10% of youth do not achieve remission despite receiving first-line treatments. This article reviews the extant, albeit limited, evidence supporting treatment approaches for youth with treatment-resistant OCD. A literature search for articles addressing pediatric treatment-resistant OCD was conducted through April 11, 2024. These results were augmented by searching for treatment-resistant OCD in adults; treatment strategies discovered for the adult population were then searched in the context of children and adolescents. In general, intensive treatment programs and antipsychotic augmentation of an antidepressant had the most substantial and consistent evidence base for treatment-resistant youth with OCD, although studies were limited and of relatively poor methodological quality (i.e., open trials, naturalistic studies). Several pharmacological approaches (clomipramine, antipsychotics [e.g., aripiprazole, risperidone], riluzole, ketamine, D-cycloserine, memantine, topiramate, N-acetylcysteine, ondansetron), largely based on supporting data among adults, have received varying levels of investigation and support. There is nascent support for how to treat pediatric treatment-resistant OCD. Future treatment studies need to consider how to manage the significant minority of youth who fail to benefit from first-line treatment approaches.

The future of psychological treatments: The Marburg Declaration

Although psychological treatments are broadly recognized as evidence-based interventions for various mental disorders, challenges remain. For example, a substantial proportion of patients receiving such treatments do not fully recover, and many obstacles hinder the dissemination, implementation, and training of psychological treatments. These problems require those in our field to rethink some of our basic models of mental disorders and their treatments, and question how research and practice in clinical psychology should progress. To answer these questions, a group of experts of clinical psychology convened at a Think-Tank in Marburg, Germany, in August 2022 to review the evidence and analyze barriers for current and future developments. After this event, an overview of the current state-of-the-art was drafted and suggestions for improvements and specific recommendations for research and practice were integrated. Recommendations arising from our meeting cover further improving psychological interventions through translational approaches, improving clinical research methodology, bridging the gap between more nomothetic (group-oriented) studies and idiographic (person-centered) decisions, using network approaches in addition to selecting single mechanisms to embrace the complexity of clinical reality, making use of scalable digital options for assessments and interventions, improving the training and education of future psychotherapists, and accepting the societal responsibilities that clinical psychology has in improving national and global health care. The objective of the Marburg Declaration is to stimulate a significant change regarding our understanding of mental disorders and their treatments, with the aim to trigger a new era of evidence-based psychological interventions.

[Treatment resistance in anxiety disorders-Definition and treatment options]

Treatment resistance in anxiety disorders represents a clinical challenge, contributes to the chronicity of the diseases as well as sequential comorbidities, and is associated with a significant individual and socioeconomic burden. This narrative review presents the operational definition of treatment resistance in anxiety disorders according to international consensus criteria (< 50% reduction in the Hamilton Anxiety Scale, HAM‑A, score or < 50% reduction in the Beck Anxiety Inventory, BAI, score or a clinical global impression-improvement, CGI‑I, score > 2). At least two unsuccessful guideline-based treatment attempts with pharmacological monotherapy or at least one unsuccessful treatment attempt with adequately delivered cognitive behavioral therapy are required. Pharmacotherapeutically, after excluding pseudo-resistance, switching the medication within one class or to another class and augmentation strategies with other antidepressants (mirtazapine, agomelatine), antipsychotics (quetiapine) or anticonvulsants (valproate) are recommended. Psychotherapeutically, third-wave therapies, psychodynamic therapy, systemic therapy and physical exercise can be considered for therapy resistance. In cases of no response to psychotherapy or pharmacotherapy, the respective other form of therapy or a combination of both should be offered. Compounds targeting the glutamatergic and endocannabinoid systems as well as neuropeptides are being tested as potential innovative pharmaceuticals for treatment-resistant anxiety disorders. There is an urgent need for further research to identify predictive markers and mechanisms as well as to develop innovative pharmacological and psychotherapeutic interventions for treatment-resistant anxiety disorders.

[Non-response to psychotherapy: concepts, problems and referral options]

AIM

In this paper we review the current literature on the clinical problem that some patients do not achieve response after adequately conducted psychotherapy. We explicate our understanding of nonresponse and treatment resistance including the operational definitions, summarize the theoretical explanations and empirical studies and put forward possible study designs and treatment options.

METHODS

Literature search using PubMed and Web of Science.

RESULTS

For the domain of psychotherapy, the term treatment resistance does not seem appropriate; instead, we use the more descriptive terms nonresponse and recurrent nonresponse. Generally, this topic is far less represented in psychotherapy than in pharmacotherapy. Controlled switching studies with a switch from pharmacotherapy to psychotherapy are rare and those switching from one psychotherapeutic approach to another are nearly nonexistent. Building on clinical considerations, we propose a flow-chart for clinical decision making after nonresponse in psychotherapy.

DISCUSSION

Learning from errors is highly beneficial. This principle should be more consistently followed up in psychotherapy research as well as in supervision and training. Guidelines should include consensual and evidence-based advice on how to deal with nonresponse and recurring nonresponse.

D-Cycloserine enhances the bidirectional range of NMDAR-dependent hippocampal synaptic plasticity

The partial N-methyl-D-aspartate receptor (NMDAR) agonist D-Cycloserine (DCS) has been evaluated for the treatment of a wide variety of psychiatric disorders, including dementia, schizophrenia, depression and for the augmentation of exposure-based psychotherapy. Most if not all of the potential psychiatric applications of DCS target an enhancement or restitution of cognitive functions, learning and memory. Their molecular correlate is long-term synaptic plasticity; and many forms of synaptic plasticity depend on the activation of NMDA receptors. Here, we comprehensively examined the modulation of different forms of synaptic plasticity in the hippocampus by DCS and its mechanism. We found that DCS positively modulates NMDAR-dependent forms of long-term synaptic plasticity (long-term synaptic potentiation, LTP, and long-term synaptic depression, LTD) in hippocampal brain slices of juvenile rats without affecting basal synaptic transmission. DCS binds to the D-serine/glycine binding site of the NMDAR. Pharmacological inhibition of this site prevented the induction of LTP, whereas agonism at the D-serine/glycine binding site augmented LTP and could functionally substitute for weak LTP induction paradigms. The most probable origin of endogenous D-serine are astrocytes, and its exocytosis is regulated by astrocytic metabotropic glutamate receptors (mGluR1). Functional eradication of astrocytes, inhibition of mGluR1 receptors and G-protein signaling in astrocytes adjacent to postsynaptic neurons prevented the induction of NMDAR-dependent forms of LTP and LTD. Our results support the enhancement of a bidirectional range of NMDAR-dependent hippocampal synaptic plasticity by DCS and D-serine-mediated gliotransmission. Therefore, the D-serine/glycine-binding site in NMDAR is a major target for psychopharmacological interventions targeting plasticity-related disorders.

Impact of virtual reality applications in the treatment of anxiety disorders: A systematic review and meta-analysis of randomized-controlled trials

BACKGROUND AND OBJECTIVES

Anxiety disorders are the most prevalent mental disorders worldwide. Virtual reality (VR) treatment approaches have increasingly been studied. Before clinical implementation, it is necessary to evaluate the treatment effect of VR applications. The objective is to evaluate the treatment effect of virtual reality applications in the treatment of anxiety disorders compared to conventional therapy.

METHODS

A systematic literature review with meta-analysis was conducted. Four databases were used to identify randomized controlled trials published between April 2011 and April 2021 which compare VR applications with non-VR interventions or waiting lists. Study characteristics, pre- and post-treatment data were extracted. Hedges g was calculated as effect size. Primary outcome was anxiety symptoms.

RESULTS

Data from 17 studies from 827 participants was extracted. The studies examined specific phobia (n = 9), social anxiety disorder (n = 4), agoraphobia (n = 2) and panic disorder (n = 2). 16 out of 17 studies used head-mounted displays as VR application. A non-significant effect size with significant heterogeneity was observed in favor of the use of VR applications in anxiety symptoms (g, 0.33; 95%-CI, -0.20-0.87). Compared to passive control groups, VR applications are associated significant with lower anxiety symptoms (g, 1.29; 95%-CI, 0.68-1.90).

LIMITATIONS

The study and patient characteristics varied between the individual studies which is reflected in a high statistical heterogeneity of the effect sizes.

CONCLUSIONS

The added value of VR applications over waiting-list or psychoeducation only control groups is obvious. VR applications can be used as part of the treatment of anxiety disorders, especially when conventional therapy is unavailable.

Adjunctive cognitive training with exposure enhances fear and neural outcomes in social anxiety

Exposure-based cognitive behavioral therapy (CBT) is the gold standard for treating social anxiety disorder (SAD), yet response is not universal. CBT is thought to operate via extinction-related learning during exposure, which in turn relies on cognitive processes such as working memory. The present proof-of-concept study investigates the potential for training working memory to improve anxiety related outcomes following exposure. Thirty-three adults with elevated social anxiety were randomized to complete a working memory training or sham training condition. Post-training, participants completed a working memory assessment, speech exposure session, and two fMRI tasks. Participants who received working memory training demonstrated lower distress ratings by the end of the speech exposures and better performance on the fMRI working memory task than those in sham. Working memory training completers had greater neural activation in frontoparietal regions during an in-scanner working memory task and exhibited less neural activation in the fusiform gyrus in response to an emotional face processing task than those in sham. Adding working memory training to exposure procedures could strengthen functioning of frontoparietal regions and alter emotional processing - key mechanisms implicated in extinction learning. Findings provide preliminary evidence that training working memory in conjunction with exposure may enhance exposure success.

Using pre-treatment de novo threat conditioning outcomes to predict treatment response to DCS augmentation of exposure-based CBT

BACKGROUND

Over a decade and a half of research has resulted in inconsistent evidence for the efficacy of d-cycloserine (DCS), a partial glutamatergic N-methyl-D-aspartate agonist, for augmenting exposure-based cognitive behavioral therapy (CBT) for anxiety- and fear-based disorders. These variable findings have motivated the search for moderators of DCS augmentation efficacy.

METHODS

In this secondary analysis of a previous randomized clinical trial, we evaluated the value of de novo threat conditioning outcomes-degree of threat acquisition, extinction, and extinction retention-for predicting treatment response to exposure-based CBT for social anxiety disorder, applied with and without DCS augmentation in a sample of 59 outpatients.

RESULTS

We found that average differential skin conductance response (SCR) during extinction and extinction retention significantly moderated the prediction of clinical response to DCS: participants with poorer extinction and extinction retention showed relatively improved treatment response with DCS. No such effects were found for expectancy ratings, consistent with accounts of DCS selectively aiding lower-order but not higher-order extinction learning.

CONCLUSIONS

These findings provide support for extinction and extinction retention outcomes from threat conditioning as potential pre-treatment biomarkers for DCS augmentation benefits. Independent of DCS augmentation, the current study did not support threat conditioning outcomes as useful for predicting response to exposure-based CBT.

Anxiety as a disorder of uncertainty: implications for understanding maladaptive anxiety, anxious avoidance, and exposure therapy

In cognitive-behavioral conceptualizations of anxiety, exaggerated threat expectancies underlie maladaptive anxiety. This view has led to successful treatments, notably exposure therapy, but is not consistent with the empirical literature on learning and choice alterations in anxiety. Empirically, anxiety is better described as a disorder of uncertainty learning. How disruptions in uncertainty lead to impairing avoidance and are treated with exposure-based methods, however, is unclear. Here, we integrate concepts from neurocomputational learning models with clinical literature on exposure therapy to propose a new framework for understanding maladaptive uncertainty functioning in anxiety. Specifically, we propose that anxiety disorders are fundamentally disorders of uncertainty learning and that successful treatments, particularly exposure therapy, work by remediating maladaptive avoidance from dysfunctional explore/exploit decisions in uncertain, potentially aversive situations. This framework reconciles several inconsistencies in the literature and provides a path forward to better understand and treat anxiety.

Pilot Study of Self-Distancing Augmentation to Exposure Therapy for Youth Anxiety

This pilot examines a self-distancing augmentation to exposure. Nine youth with anxiety (ages 11-17; 67% female) completed treatment. The study employed a brief (eight session) crossover ABA/BAB design. Exposure difficulty, engagement with exposure, and treatment acceptability were examined as primary outcome variables. Visual inspection of plots indicated that youth completed more difficult exposures during augmented exposure sessions [EXSD] than classic exposure sessions [EX] by therapist- and youth-report and that therapists reported higher youth engagement during EXSD than EX sessions. There were no significant differences between EXSD and EX on exposure difficulty or engagement by therapist- or youth-report. Treatment acceptability was high, although some youth reported that self-distancing was "awkward". Self-distancing may be associated with increased exposure engagement and willingness to complete more difficult exposures, which has been linked to treatment outcomes. Future research is needed to further demonstrate this link, and link self-distancing to outcomes directly.

A transdiagnostic meta-analysis of acute augmentations to psychological therapy

At least half of all patients with mental health disorders do not respond adequately to psychological therapy. Acutely enhancing particular biological or psychological processes during psychological therapy may improve treatment outcomes. However, previous studies are confined to specific augmentation approaches, typically assessed within single diagnostic categories. Our objective was to assess to what degree acute augmentations of psychological therapy reduce psychiatric symptoms and estimate effect sizes of augmentation types (for example, brain stimulation or psychedelics). We searched Medline, PsycINFO and Embase for controlled studies published between database inception and 25 May 2022. We conducted a preregistered random-effects meta-analysis (PROSPERO CRD42021236403). We identified 108 studies (N = 5,889). Acute augmentation significantly reduced the severity of mental health problems (Hedges' g = -0.27, 95% CI: [-0.36, -0.18]; P < 0.0001), particularly for the transdiagnostic dimensions 'Fear' and 'Distress'. This result survived a trim-and-fill analysis to account for publication bias. Subgroup analyses revealed that pharmacological, psychological and somatic augmentations were effective, but to varying degrees. Acute augmentation approaches are a promising route to improve outcomes from psychological therapy.

[Combination of ketamine and esketamine with Exposure and Response Prevention (ERP) therapy for Obsessive-Compulsive Disorder]

Obsessive-Compulsive Disorder (OCD), characterized by the combination of obsession and compulsion, is a clinical and therapeutic challenge. Many patients with OCD do not respond to first-line treatments such as serotonin selective reuptake inhibitors (SSRIs) and exposure and response prevention psychotherapy (ERP). For these resistant patients, some preliminary studies have shown that ketamine, a non-selective glutamatergic NMDA receptors antagonist, could improve the obsessive symptoms. A number of these studies have also suggested that the combination of ketamine with ERP psychotherapy may jointly potentiate the effectiveness of ketamine and ERP. In this paper, we present the existing data on the combined use of ketamine with ERP psychotherapy for OCD. We suggest that modulation of NMDA receptor activity and glutamatergic signaling by ketamine may promote the therapeutic mechanisms involved in ERP such as fear extinction and brain plasticity mechanisms. Finally, we propose a ketamine-augmented ERP psychotherapy (KAP-ERP) protocol in OCD, and we present the limitations associated with its application in clinical practice.

Alleviating anxiety and taming trauma: Novel pharmacotherapeutics for anxiety disorders and posttraumatic stress disorder

Psychiatric disorders associated with psychological trauma, stress and anxiety are a highly prevalent and increasing cause of morbidity worldwide. Current therapeutic approaches, including medication, are effective in alleviating symptoms of anxiety disorders and posttraumatic stress disorder (PTSD), at least in some individuals, but have unwanted side-effects and do not resolve underlying pathophysiology. After a period of stagnation, there is renewed enthusiasm from public, academic and commercial parties in designing and developing drug treatments for these disorders. Here, we aim to provide a snapshot of the current state of this field that is written for neuropharmacologists, but also practicing clinicians and the interested lay-reader. After introducing currently available drug treatments, we summarize recent/ongoing clinical assessment of novel medicines for anxiety and PTSD, grouped according to primary neurochemical targets and their potential to produce acute and/or enduring therapeutic effects. The evaluation of putative treatments targeting monoamine (including psychedelics), GABA, glutamate, cannabinoid, cholinergic and neuropeptide systems, amongst others, are discussed. We emphasize the importance of designing and clinically assessing new medications based on a firm understanding of the underlying neurobiology stemming from the rapid advances being made in neuroscience. This includes harnessing neuroplasticity to bring about lasting beneficial changes in the brain rather than - as many current medications do - produce a transient attenuation of symptoms, as exemplified by combining psychotropic/cognitive enhancing drugs with psychotherapeutic approaches. We conclude by noting some of the other emerging trends in this promising new phase of drug development.

Aerobic exercise after extinction learning reduces return of fear and enhances memory of items encoded during extinction learning

Fear conditioning paradigms are widely used in laboratory settings to discover treatments that enhance memory consolidation and various fear processes (extinction learning, limit return of fear) that are relevant targets of exposure-based therapies. However, traditional lab-based paradigms often use the exact same conditioned stimuli for acquisition and extinction (typically differentiated with a context manipulation), whereas the opposite is true in clinical settings, as exposure therapy rarely (if ever) uses precisely the exact same stimuli from an individual's learning history. Accordingly, this study utilized a novel three-day category-based fear conditioning protocol (that uses categories of non-repeating objects [animals and tools] as conditioned stimuli during fear conditioning and extinction) to determine if aerobic exercise enhances the consolidation of extinction learning (reduces return of fear) and memory (for items encoded during extinction) during subsequent tests of extinction recall. Participants (n=40) completed a fear acquisition (day 1), fear extinction (day 2), and extinction recall (day 3) protocol. On day 1, participants completed a fear acquisition task in which they were trained to associate a category of conditioned stimuli (CS+) with the occurrence of an unconditioned stimulus (US). On day 2, participants were administered a fear extinction procedure during which CS+ and CS- categorical stimuli were presented in absence of the occurrence of the US. After completing the task, participants were randomly assigned to either receive moderate-intensity aerobic exercise (EX) or a light-intensity control (CON) condition. On day 3, participants completed fear recall tests (during which day 1, day 2, and novel CS+ and CS- stimuli were presented). Fear responding was assessed via threat expectancy ratings and skin conductance responses (SCR). During the fear recall tests, the EX group reported significantly lower threat expectancy ratings to the CS+ and CS- and exhibited greater memory of CS+ and CS- stimuli that were previously presented during day 2. There were no significant group differences for SCR. These results suggests that administration of moderate-intensity aerobic exercise following extinction learning contributes to reduced threat expectancies during tests of fear recall and enhanced memory of items encoded during extinction.

Is Fear Extinction Impairment Central to Psychopathology?

As discussed in this chapter, there have been enormous advances in our understanding of how anxiety disorders develop, are maintained, and can be treated. Many of these advances have been the result of translational studies using fear conditioning and extinction models. Despite these successes, we recognize, as a field, that there are important limitations in the extent to which extinction can explain how anxiety disorders and behaviors remit. Clinically speaking, the outstanding challenge for treatment of anxiety disorders is to improve the current suboptimal success rates. Over the past 30 years, we have not improved our treatment success rates despite employing many pharmacological and pharmacological strategies. While extinction and related fear circuitry mechanisms most certainly appear to play a role in treatment of anxiety disorders, they are also apparently insufficient to fully accommodate the varied responses individuals exhibit with this treatment approach. Increasingly diverse and innovative approaches are needed that accommodate the multitude of change mechanisms involved in treating anxiety. However, this is not to suggest ignoring the key role that extinction and memory updating processes play in overcoming anxiety.

Treatment of disgust in specific emotional disorders

Although conditioning approaches have highlighted potential characteristics of disgust in anxiety disorders, obsessive-compulsive disorder (OCD), and posttraumatic stress disorder (PTSD), these findings have yet to be translated into evidence-based treatments. Examination of the literature suggests various indicators of disgust that predict treatment outcome in these disorders. However, mechanisms remain unclear because studies examining disgust during the course of treatment are limited. Increasingly, the field has moved toward experimental investigation of strategies that reduce disgust. While cognitive reappraisal and imagery techniques appear promising, such techniques have yet to be examined as anxiety disorder treatments in large-scale randomized clinical trials. The literature also points to novel approaches to treating disgust, ranging from an inhibitory-informed approach to exposure therapy to transcranial direct current stimulation. However, the development of novel treatment approaches will require more rigorous experimental psychopathology approaches that can further elucidate processes that contribute to the etiology and/or maintenance of disorders of disgust.

Causally mapping human threat extinction relevant circuits with depolarizing brain stimulation methods

Laboratory threat extinction paradigms and exposure-based therapy both involve repeated, safe confrontation with stimuli previously experienced as threatening. This fundamental procedural overlap supports laboratory threat extinction as a compelling analogue of exposure-based therapy. Threat extinction impairments have been detected in clinical anxiety and may contribute to exposure-based therapy non-response and relapse. However, efforts to improve exposure outcomes using techniques that boost extinction - primarily rodent extinction - have largely failed to date, potentially due to fundamental differences between rodent and human neurobiology. In this review, we articulate a comprehensive pre-clinical human research agenda designed to overcome these failures. We describe how connectivity guided depolarizing brain stimulation methods (i.e., TMS and DBS) can be applied concurrently with threat extinction and dual threat reconsolidation-extinction paradigms to causally map human extinction relevant circuits and inform the optimal integration of these methods with exposure-based therapy. We highlight candidate targets including the amygdala, hippocampus, ventromedial prefrontal cortex, dorsal anterior cingulate cortex, and mesolimbic structures, and propose hypotheses about how stimulation delivered at specific learning phases could strengthen threat extinction.

Enhancing Fear Extinction: Pharmacological Approaches

Extinction is the process by which the memory of a learned conditioned association decreases over time and with introduction of new associations. It is a vital part of fear learning, and it is critical to recovery in multiple fear-related disorders, including Specific and Social Phobias, Panic Disorder, Obsessive Compulsive Disorder (OCD), and Posttraumatic Stress Disorder (PTSD). The process of extinction is also the underlying mechanism for recovery in gold-standard therapies for PTSD, including prolonged exposure, cognitive processing therapy, eye movement desensitization and procession, as well as other empirically-based paradigms. Pharmacological modulators of extinction are thus promising targets for treatment of fear-related disorders. We focus here on emerging psychopharmacological treatments to facilitate extinction: D-cycloserine, scopolamine, losartan, ketamine, and 3,4-methylenedioxymethamphetamine. We also provide an overview of recent advances in molecular pathways that show promise as targets for extincion and inhibitory learning, including pathways related to cannabinoid, brain-derived neurotrophic factor, hypothalamic-pituitary-adrenal signaling, and promising work in neurosteroid compounds.

Understanding Human Fear Extinction: Insights from Psychophysiology

The study of fear extinction has been driven largely by Pavlovian fear conditioning methods across the translational spectrum. The primary methods used to study these processes in humans have been recordings of skin conductance (historically termed galvanic skin response) and fear-potentiation of the acoustic startle reflex. As outlined in the following chapter, the combined corpus of this work has demonstrated the value of psychophysiology in better understanding the underlying neurobiology of extinction learning in healthy humans as well as those with psychopathologies. In addition, psychophysiological approaches, which allow for the preservation of methods between species, have shown their applicability to the assessment of wide-ranging treatment effects. The chapter concludes with potential trajectories for future study in this area.

Test–retest reliability of human threat conditioning and generalization across a 1‐to‐2‐week interval

Given the increasing use of threat conditioning and generalization for clinical-translational research efforts, establishing test-retest reliability of these paradigms is necessary. Specifically, it is an empirical question whether the same participant evinces a similar generalization gradient of conditioned responses across two sessions with the identical contingencies and stimuli. Here, 46 human volunteers participated in an identical auditory threat acquisition and generalization protocol at two sessions separated by 1-to-2 weeks. Skin conductance responses (SCR) and trial-by-trial shock risk ratings served as primary measures. We used linear mixed effects modeling to test differential threat responses and generalization gradients, and Generalizability (G) theory coefficients as our primary formal assessment of test-retest reliability of intraindividual stability and change across time. Results showed largely invariant differential conditioning and generalization gradients across time. G coefficients indicated fair reliability for acquisition and generalization SCR. In contrast, risk rating reliabilities were mixed, and reliability was particularly low for acquisition risk ratings. Our findings generally support reliability of the threat conditioning and generalization paradigm for shorter test-retest intervals and highlight their utility for assessments of behavioral interventions in mental health research, but challenges remain and further work is needed. Threat conditioning and generalization tasks are increasingly used for translational efforts to improve behavioral interventions, and thus test-retest reliability for these tasks needs to be established. Our results support the test-retest reliability of threat conditioning and generalization over a relatively short (1-to-2 week) interval, but this depends on the measure used (physiological vs. self-report). Overall, these tasks could be appropriate for repeated testing over the course of a short-duration intervention study, but more research is needed, particularly in regard to longer-duration studies.

Mechanisms of Action in Exposure Therapy

PURPOSE OF REVIEW

Exposure therapy is an effective treatment for anxiety-related disorders, but many individuals do not achieve full symptom relief, and return of fear is a common occurrence. Understanding how exposure therapy works enables further development of strategies to improve its effectiveness.

RECENT FINDINGS

Recent studies have examined mechanisms of exposure-based interventions across multiple levels of analysis, from cognitive and behavioral changes that occur during treatment to the neurobiological mechanisms underlying fear extinction. Belief change and reductions in safety behaviors and avoidance mediate symptom improvements during exposure therapy, suggesting plausible cognitive and behavioral mechanisms. On the neural level, increased activation of prefrontal regions during extinction learning is a likely mechanism of exposure. Improved understanding of the biological mechanisms of exposure have led to exciting developments in clinical research, including pharmacological augmentation, though clinical translation of basic research has produced mixed results. Though still in development, such translational research is a promising future direction for exposure-based interventions.

Efficacy of Adjunctive D-Cycloserine to Intermittent Theta-Burst Stimulation for Major Depressive Disorder: A Randomized Clinical Trial

Importance

The antidepressant effects of transcranial magnetic stimulation protocols for major depressive disorder (MDD) are thought to depend on synaptic plasticity. The theta-burst stimulation (TBS) protocol synaptic plasticity is known to be N-methyl-D-aspartate (NMDA)-receptor dependent, yet it is unknown whether enhancing NMDA-receptor signaling improves treatment outcomes in MDD.

Objective

To test whether low doses of the NMDA-receptor partial-agonist, D-cycloserine, would enhance intermittent TBS (iTBS) treatment outcomes in MDD.

Design, Setting, and Participants

This was a single-site 4-week, double-blind, placebo-controlled, randomized clinical trial conducted from November 6, 2019, to December 24, 2020, including 50 participants with MDD. Participants were recruited via advertisements and referral. Inclusion criteria were as follows: age 18 to 65 years with a primary diagnosis of MDD, a major depressive episode with score of 18 or more on the 17-item Hamilton Depression Rating Scale, a Young Mania Rating Scale score of 8 or less, and normal blood work (including complete blood cell count, electrolytes, liver function tests, and creatinine level).

Interventions

Participants were randomly assigned 1:1 to either iTBS plus placebo or iTBS plus D-cycloserine (100 mg) for the first 2 weeks followed by iTBS without an adjunct for weeks 3 and 4.

Main Outcomes and Measures

The primary outcome was change in depressive symptoms as measured by the Montgomery-Åsberg Depression Rating Scale (MADRS) at the conclusion of treatment. Secondary outcomes included clinical response, clinical remission, and Clinical Global Impression (CGI) scores.

Results

A total of 50 participants (mean [SD] age, 40.8 [13.4] years; 31 female [62%]) were randomly assigned to treatment groups: iTBS plus placebo (mean [SD] baseline score, 30.3 [4.2]) and iTBS plus D-cycloserine (mean [SD] baseline score, 30.4 [4.5]). The iTBS plus D-cycloserine group had greater improvements in MADRS scores compared with the iTBS plus placebo group (mean difference, -6.15; 95% CI, -2.43 to -9.88; Hedges g = 0.99; 95% CI, 0.34-1.62). Rates of clinical response were higher in the iTBS plus D-cycloserine group than in the iTBS plus placebo group (73.9% vs 29.3%), as were rates of clinical remission (39.1% vs 4.2%). This was reflected in lower CGI-severity ratings and greater CGI-improvement ratings. No serious adverse events occurred.

Conclusions and Relevance

Findings from this clinical trial indicate that adjunctive D-cycloserine may be a promising strategy for enhancing transcranial magnetic stimulation treatment outcomes in MDD using iTBS requiring further investigation.

Trial Registration

ClinicalTrials.gov Identifier: NCT03937596.

A systematic review of the pharmacological modulation of autobiographical memory specificity

Background

Over-general autobiographical memory (AM) retrieval is proposed to have a causal role in the maintenance of psychological disorders like depression and PTSD. As such, the identification of drugs that modulate AM specificity may open up new avenues of research on pharmacological modeling and treatment of psychological disorders.

Aim

The current review summarizes randomized, placebo-controlled studies of acute pharmacological modulation of AM specificity.

Method

A systematic search was conducted of studies that examined the acute effects of pharmacological interventions on AM specificity in human volunteers (healthy and clinical participants) measured using the Autobiographical Memory Test.

Results

Seventeen studies were identified (986 total participants), of which 16 were judged to have low risk of bias. The presence and direction of effects varied across drugs and diagnostic status of participants (clinical vs. healthy volunteers). The most commonly studied drug-hydrocortisone-produced an overall impairment in AM specificity in healthy volunteers [g = -0.28, CI (-0.53, -0.03), p = 0.03], although improvements were reported in two studies of clinical participants. In general, studies of monoamine modulators reported no effect on specificity.

Conclusion

Pharmacological enhancement of AM specificity is inconsistent, although monaminergic modulators show little promise in this regard. Drugs that reduce AM specificity in healthy volunteers may be useful experimental-pharmacological tools that mimic an important transdiagnostic impairment in psychological disorders.

Systematic review registration

PROSPERO, identifier CRD42020199076, https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020199076.

A randomized pharmacological fMRI trial investigating D-cycloserine and brain plasticity mechanisms in learned pain responses

Learning and negative outcome expectations can increase pain sensitivity, a phenomenon known as nocebo hyperalgesia. Here, we examined how a targeted pharmacological manipulation of learning would impact nocebo responses and their brain correlates. Participants received either a placebo (n = 27) or a single 80 mg dose of D-cycloserine (a partial NMDA receptor agonist; n = 23) and underwent fMRI. Behavioral conditioning and negative suggestions were used to induce nocebo responses. Participants underwent pre-conditioning outside the scanner. During scanning, we first delivered baseline pain stimulations, followed by nocebo acquisition and extinction phases. During acquisition, high intensity thermal pain was paired with supposed activation of sham electrical stimuli (nocebo trials), whereas moderate pain was administered with inactive electrical stimulation (control trials). Nocebo hyperalgesia was induced in both groups (p < 0.001). Nocebo magnitudes and brain activations did not show significant differences between D-cycloserine and placebo. In acquisition and extinction, there were significantly increased activations bilaterally in the amygdala, ACC, and insula, during nocebo compared to control trials. Nocebo acquisition trials also showed increased vlPFC activation. Increased opercular activation differentiated nocebo-augmented pain aggravation from baseline pain. These results support the involvement of integrative cognitive-emotional processes in nocebo hyperalgesia.

The global assessment of OCD

Obsessive Compulsive Disorder (OCD) is a common mental disorder that often causes great sufferance, with substantial impairment in social functioning and quality of life and affects family and significant relationships. Notwithstanding its severity, OCD is often not adequately diagnosed, or it is diagnosed with delay, leading often to a long latency between onset of the OCD symptoms and the start of adequate treatments. Several factors contribute to the complexity of OCD's clinical picture: early age of onset, chronic course, heterogeneity of symptoms, high rate of comorbidity with other psychiatric disorders, slow or partial response to therapy. Therefore, it is of primary importance for clinicians involved in diagnosing OCD, to assess all aspects of the disorder. This narrative review focuses on the global assessment of OCD, highlighting crucial areas to explore, pointing out the clinical features which are relevant for the treatment of the disorder, and giving an overview of the psychometric tools that can be useful during the screening procedure.

Randomized controlled experimental study of hydrocortisone and D-cycloserine effects on fear extinction in PTSD

Fear extinction underlies prolonged exposure, one of the most well-studied treatments for posttraumatic stress disorder (PTSD). There has been increased interest in exploring pharmacological agents to enhance fear extinction learning in humans and their potential as adjuncts to PE. The objective of such adjuncts is to augment the clinical impact of PE on the durability and magnitude of symptom reduction. In this study, we examined whether hydrocortisone (HC), a corticosteroid, and D-Cycloserine (DCS), an N-methyl-D-aspartate receptor partial agonist, enhance fear extinction learning and consolidation in individuals with PTSD. In a double-blind placebo-controlled 3-group experimental design, 90 individuals with full or subsyndromal PTSD underwent fear conditioning with stimuli that were paired (CS+) or unpaired (CS-) with shock. Extinction learning occurred 72 h later and extinction retention was tested one week after extinction. HC 25 mg, DCS 50 mg or placebo was administered one hour prior to extinction learning. During extinction learning, the DCS and HC groups showed a reduced differential CS+/CS- skin conductance response (SCR) compared to placebo (b = -0.19, CI = -0.01 to -37, p = 0.042 and b = -0.25, CI = -08 to -0.43, p = 0.005, respectively). A nonsignificant trend for a lower differential CS+/CS- SCR in the DCS group, compared to placebo, (b = -0.25, CI = 0.04 to -0.55, p = 0.089) was observed at retention testing, one week later. A single dose of HC and DCS facilitated fear extinction learning in participants with PTSD symptoms. While clinical implications have yet to be determined, our findings suggest that glucocorticoids and NMDA agonists hold promise for facilitating extinction learning in PTSD.

The elegant complexity of fear in non-human animals

Activation of the fear system is adaptive, and protects individuals from impending harm; yet, exacerbation of the fear system is at the source of anxiety-related disorders. Here, we briefly review the 'why' and 'how' of fear, with an emphasis on models that encapsulate the elegant complexity of rodents' behavioral responding in the face of impending harm, and its relevance to developing treatment interventions.

The role of attention control in complex real-world tasks

Working memory capacity is an important psychological construct, and many real-world phenomena are strongly associated with individual differences in working memory functioning. Although working memory and attention are intertwined, several studies have recently shown that individual differences in the general ability to control attention is more strongly predictive of human behavior than working memory capacity. In this review, we argue that researchers would therefore generally be better suited to studying the role of attention control rather than memory-based abilities in explaining real-world behavior and performance in humans. The review begins with a discussion of relevant literature on the nature and measurement of both working memory capacity and attention control, including recent developments in the study of individual differences of attention control. We then selectively review existing literature on the role of both working memory and attention in various applied settings and explain, in each case, why a switch in emphasis to attention control is warranted. Topics covered include psychological testing, cognitive training, education, sports, police decision-making, human factors, and disorders within clinical psychology. The review concludes with general recommendations and best practices for researchers interested in conducting studies of individual differences in attention control.

Enhancing exposure therapy for posttraumatic stress disorder (PTSD): a randomized clinical trial of virtual reality and imaginal exposure with a cognitive enhancer

Posttraumatic stress disorder (PTSD) is a significant public health issue. Yet, there are limited treatment options and no data to suggest which treatment will work for whom. We tested the efficacy of virtual reality exposure (VRE) or prolonged imaginal exposure (PE), augmented with D-cycloserine (DCS) for combat-related PTSD. As an exploratory aim, we examined whether brain-derived neurotrophic factor (BDNF) and fatty acid amide hydrolase (FAAH) moderated treatment response. Military personnel with PTSD (n = 192) were recruited into a multisite double-blind randomized controlled trial to receive nine weeks of VRE or PE, with DCS or placebo. Primary outcome was the improvement in symptom severity. Randomization was stratified by comorbid depression (MDD) and site. Participants in both VRE and PE showed similar meaningful clinical improvement with no difference between the treatment groups. A significant interaction (p = 0.45) suggested VRE was more effective for depressed participants (CAPS difference M = 3.51 [95% CI 1.17-5.86], p = 0.004, ES = 0.14) while PE was more effective for nondepressed participants (M = -8.87 [95% CI -11.33 to -6.40], p < 0.001, ES = -0.44). The main effect of DCS vs. placebo was not significant. Augmentation by MDD interaction (p = 0.073) suggested that depressed participants improved more on placebo (M = -8.43 [95% CI -10.98 to -5.88], p < 0.001, ES = -0.42); DCS and placebo were equally effective for nondepressed participants. There was an apparent moderating effect of BDNF Val66Met polymorphism on DCS augmentation (ES = 0.67). Met66 allele carriers improved more on DCS (ES = -0.25). FAAH 385 A carriers improved more than non-carriers (ES = 0.33), particularly those with MDD (ES = 0.62). This study provides a step toward precision therapeutics for PTSD by demonstrating that comorbid MDD and genetic markers may help guide treatment selection.ClinicalTrials.gov Identifier: NCT01352637.

A Case for Translation From the Clinic to the Laboratory

Laboratory procedures have been used for decades as analogues for clinical processes with the goal of improving our understanding of psychological treatments for emotional disorders and identifying strategies to make treatments more effective. This research has often focused on translation from the laboratory to the clinic. Although this approach has notable successes, it has not been seamless. There are many examples of strategies that work in the laboratory that fail to lead to improved outcomes when applied clinically. One possible reason for this gap between experimental and clinical research is a failure to focus on translation from the clinic to the laboratory. Here, we discuss potential benefits of translation from the clinic to the laboratory and provide examples of how this might be implemented. We first consider two well-established laboratory analogues (extinction and cognitive reappraisal), identify critical aspects of the related clinical procedures (exposure and cognitive restructuring) that are missing from these analogues, and propose variations to better capture the clinical process. Second, we discuss two clinical procedures that have more recently been brought into the laboratory (eye-movement desensitization and reprocessing and imagery rescripting). We conclude by highlighting potential implications of this proposed shift in focus for translational research.

Rational and Translational Implications of D-Amino Acids for Treatment-Resistant Schizophrenia: From Neurobiology to the Clinics

Schizophrenia has been conceptualized as a neurodevelopmental disorder with synaptic alterations and aberrant cortical–subcortical connections. Antipsychotics are the mainstay of schizophrenia treatment and nearly all share the common feature of dopamine D2 receptor occupancy, whereas glutamatergic abnormalities are not targeted by the presently available therapies. D-amino acids, acting as N-methyl-D-aspartate receptor (NMDAR) modulators, have emerged in the last few years as a potential augmentation strategy in those cases of schizophrenia that do not respond well to antipsychotics, a condition defined as treatment-resistant schizophrenia (TRS), affecting almost 30–40% of patients, and characterized by serious cognitive deficits and functional impairment. In the present systematic review, we address with a direct and reverse translational perspective the efficacy of D-amino acids, including D-serine, D-aspartate, and D-alanine, in poor responders. The impact of these molecules on the synaptic architecture is also considered in the light of dendritic spine changes reported in schizophrenia and antipsychotics’ effect on postsynaptic density proteins. Moreover, we describe compounds targeting D-amino acid oxidase and D-aspartate oxidase enzymes. Finally, other drugs acting at NMDAR and proxy of D-amino acids function, such as D-cycloserine, sarcosine, and glycine, are considered in the light of the clinical burden of TRS, together with other emerging molecules.

Efficacy of D-cycloserine augmented brief intensive cognitive-behavioural therapy for paediatric obsessive-compulsive disorder: A randomised clinical trial

OBJECTIVE

To examine the efficacy of weight-adjusted D-cycloserine (DCS) (35 or 70 mg) relative to placebo augmentation of intensive exposure therapy for youth with obsessive-compulsive disorder (OCD) in a double-blind, randomised controlled trial, and examine whether antidepressant medication or patient age moderated outcomes.

METHODS

Youth (n = 100, 7-17 years) with OCD were randomised in a 1:1 ratio to either DCS + exposure (n = 49) or placebo + exposure (n = 51). Assessments occurred posttreatment, 1 month later, and at 3 and 6 months. Pills were ingested immediately before sessions.

RESULTS

Significant improvements on all outcomes were observed at posttreatment, and to 6-month follow-up. Treatment arms did not differ across time, with no significant time-by-medication interactions on symptom severity (T1 to T2 estimate: 9.3, 95% confidence interval [CI]: -11.2 to -7.4, and estimate -10.7, 95% CI: -12.6 to -8.7), diagnostic severity (T1 to T2 estimate: -2.0, 95% CI: -2.4 to -1.5 and estimate -2.5, 95% CI: -3.0 to -2.0) or global functioning (T1 to T2 estimate: 13.8, 95% CI: 10.6 to 17.0, and estimate 16.6, 95% CI: 13.2 to 19.9). Neither antidepressants at baseline nor age moderated primary outcomes. There were significantly fewer responders/remitters at 1- and 6-month follow-up among youth in the DCS condition stabilised on SSRIs, relative to youth not taking SSRIs.

CONCLUSIONS

DCS augmented intensive exposure therapy did not result in overall additional benefits relative to placebo. Intensive exposure proved effective in reducing symptoms for the overall sample.

Potential processes of change in MDMA-Assisted therapy for social anxiety disorder: Enhanced memory reconsolidation, self-transcendence, and therapeutic relationships

OBJECTIVE

Researchers have suggested that psychotherapy may be enhanced by the addition of 3,4-methylenedioxymethamphetamine (MDMA), particularly in the treatment of disorders wherein interpersonal dysfunction is central, such as social anxiety disorder. We review literature pertaining to three potential processes of change that may be instigated during sessions involving MDMA administration in the treatment of social anxiety disorder.

DESIGN

This is a narrative review that integrates research on the etiology and maintenance of social anxiety disorder and mechanisms of action of MDMA to examine how MDMA may enhance psychotherapy outcomes.

RESULTS

We first outline how MDMA may enhance memory reconsolidation in social anxiety disorder. We then discuss how MDMA may induce experiences of self-transcendence and self-transcendent emotions such as compassion, love, and awe; and how these experiences may be therapeutic in the context of social anxiety disorder. We subsequently discuss the possibility that MDMA may enhance the strength and effectiveness of the therapeutic relationship which is a robust predictor of outcomes across many disorders as well as a potential key ingredient in treating disorders where shame and social disconnection are central factors.

CONCLUSION

We discuss how processes of change may extend beyond the MDMA dosing sessions themselves.

The influence of FAAH genetic variation on physiological, cognitive, and neural signatures of fear acquisition and extinction learning in women with PTSD

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PTSD is often treated with psychotherapies based on principles of fear acquisition and extinction.

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Increased AEA has resulted in enhanced extinction learning and recall among healthy adults.

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These effects have not yet been comprehensively examined in a PTSD population.

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Results suggest that genetic variation within the FAAH gene affects how fear learning is tuned in women with PTSD.

Background

Posttraumatic Stress Disorder (PTSD) is commonly treated with exposure-based cognitive therapies that are based on the principles of fear acquisition and extinction learning. Elevations in one of the major endocannabinoids (anandamide) either via inhibition of the primary degrading enzyme (fatty acid amide hydrolase; FAAH) or via a genetic variation in the FAAH gene (C385A; rs324420) has resulted in accelerated extinction learning and enhanced extinction recall among healthy adults. These results suggest that targeting FAAH may be a promising therapeutic approach for PTSD. However, these effects have not yet been comprehensively examined in a PTSD population.

Methods

The current study examined whether genetic variation in the FAAH gene (CC [n = 49] vs AA/AC [n = 36] allele carriers) influences physiological (skin conductance), cognitive (threat expectancy), and neural (network and voxel-wise activation) indices of fear acquisition and extinction learning among a sample of adult women with PTSD (N = 85).

Results

The physiological, cognitive, and neural signatures of fear acquisition and extinction learning varied as a function of whether or not individuals possess the FAAH C385A polymorphism. For instance, we report divergent responding between CC and AA/AC allele carriers to CS + vs CS- in limbic and striatum networks and overall greater activation throughout the task among AA/AC allele carriers in several regions [e.g., inferior frontal, middle frontal, parietal] that are highly consistent with a frontoparietal network involved in higher-order executive functions.

Conclusions

These results suggest that genetic variation within the FAAH gene influences physiological, cognitive, and neural signatures of fear learning in women with PTSD. In order to advance our understanding of the efficacy of FAAH inhibition as a treatment for PTSD, future clinical trials in this area should assess genetic variation in the FAAH gene in order to fully depict and differentiate the acute effects of a drug manipulation (FAAH inhibition) from more chronic (genetic) influences on fear extinction processes.

Parsing neural circuits of fear learning and extinction across basic and clinical neuroscience: Towards better translation

Over the past decades, studies of fear learning and extinction have advanced our understanding of the neurobiology of threat and safety learning. Animal studies can provide mechanistic/causal insights into human brain regions and their functional connectivity involved in fear learning and extinction. Findings in humans, conversely, may further enrich our understanding of neural circuits in animals by providing macroscopic insights at the level of brain-wide networks. Nevertheless, there is still much room for improvement in translation between basic and clinical research on fear learning and extinction. Through the lens of neural circuits, in this article, we aim to review the current knowledge of fear learning and extinction in both animals and humans, and to propose strategies to fill in the current knowledge gap for the purpose of enhancing clinical benefits.

Selective δ-Opioid Receptor Agonist, KNT-127, Facilitates Contextual Fear Extinction via Infralimbic Cortex and Amygdala in Mice

Facilitation of fear extinction is a desirable action for the drugs to treat fear-related diseases, such as posttraumatic stress disorder (PTSD). We previously reported that a selective agonist of the δ-opioid receptor (DOP), KNT-127, facilitates contextual fear extinction in mice. However, its site of action in the brain and the underlying molecular mechanism remains unknown. Here, we investigated brain regions and cellular signaling pathways that may mediate the action of KNT-127 on fear extinction. Twenty-four hours after the fear conditioning, mice were reexposed to the conditioning chamber for 6 min as extinction training (reexposure 1). KNT-127 was microinjected into either the basolateral nucleus of the amygdala (BLA), hippocampus (HPC), prelimbic (PL), or infralimbic (IL) subregions of the medial prefrontal cortex, 30 min before reexposure 1. Next day, mice were reexposed to the chamber for 6 min as memory testing (reexposure 2). KNT-127 that infused into the BLA and IL, but not HPC or PL, significantly reduced the freezing response in reexposure 2 compared with those of control. The effect of KNT-127 administered into the BLA and IL was antagonized by pretreatment with a selective DOP antagonist. Further, the effect of KNT-127 was abolished by local administration of MEK/ERK inhibitor into the BLA, and PI3K/Akt inhibitor into the IL, respectively. These results suggested that the effect of KNT-127 was mediated by MEK/ERK signaling in the BLA, PI3K/Akt signaling in the IL, and DOPs in both brain regions. Here, we propose that DOPs play a role in fear extinction via distinct signaling pathways in the BLA and IL.

Hallucinogenic drugs and their potential for treating fear-related disorders: Through the lens of fear extinction

Fear-related disorders, mainly phobias and post-traumatic stress disorder, are highly prevalent, debilitating disorders that pose a significant public health problem. They are characterized by aberrant processing of aversive experiences and dysregulated fear extinction, leading to excessive expression of fear and diminished quality of life. The gold standard for treating fear-related disorders is extinction-based exposure therapy (ET), shown to be ineffective for up to 35% of subjects. Moreover, ET combined with traditional pharmacological treatments for fear-related disorders, such as selective serotonin reuptake inhibitors, offers no further advantage to patients. This prompted the search for ways to improve ET outcomes, with current research focused on pharmacological agents that can augment ET by strengthening fear extinction learning. Hallucinogenic drugs promote reprocessing of fear-imbued memories and induce positive mood and openness, relieving anxiety and enabling the necessary emotional engagement during psychotherapeutic interventions. Mechanistically, hallucinogens induce dynamic structural and functional neuroplastic changes across the fear extinction circuitry and temper amygdala's hyperreactivity to threat-related stimuli, effectively mitigating one of the hallmarks of fear-related disorders. This paper provides the first comprehensive review of hallucinogens' potential to alleviate symptoms of fear-related disorders by focusing on their effects on fear extinction and the underlying molecular mechanisms. We overview both preclinical and clinical studies and emphasize the advantages of hallucinogenic drugs over current first-line treatments. We highlight 3,4-methylenedioxymethamphetamine and ketamine as the most effective therapeutics for fear-related disorders and discuss the potential molecular mechanisms responsible for their potency with implications for improving hallucinogen-assisted psychotherapy.

Augmentation of Psychotherapy with Neurobiological Methods: Current State and Future Directions

BACKGROUND

Psychotherapy and pharmacotherapy are first-line treatments for mental disorders. Despite recent improvements, only approximately 50% of the patients reach sustained remission, indicating a need for novel developments. The main concept put forward in this systematic review and hypothesis article is the targeted co-administration of defined neurobiological interventions and specific psychotherapeutic techniques.

METHODS

We conducted a systematic literature search for randomized controlled trials comparing the efficacy of augmented psychotherapy to psychotherapy alone.

RESULTS

Thirty-five trials fulfilled the inclusion criteria. The majority (29 trials) used augmentation strategies such as D-cycloserine, yohimbine, or sleep to enhance the effects of exposure therapy for anxiety disorders. Fewer studies investigated noninvasive brain stimulation with the aim of improving cognitive control, psychedelic compounds with the aim of enhancing existentially oriented psychotherapy, and oxytocin to improve social communication during psychotherapy. Results demonstrate small augmentation effects for the enhancement of exposure therapy - however, some of the studies found negative results. Other methods are less thoroughly researched, and results are mixed.

CONCLUSIONS

This approach provides an open matrix for further research and has the potential to systematically guide future studies.

Cathodal transcranial direct current stimulation on the prefrontal cortex applied after reactivation attenuates fear memories and prevent reinstatement after extinction

BACKGROUND

In the last decade, pharmacological strategies targeting reconsolidation after memory retrieval have shown promising efforts to attenuate persistent memories and overcome fear recovery. However, most reconsolidation inhibiting agents have not been approved for human testing. While non-invasive neuromodulation can be considered an alternative approach to pharmacological treatments, there is a lack of evidence about the efficacy of these technologies when modifying memory traces via reactivation/reconsolidation mechanism.

OBJECTIVE

In this study, we evaluate the effect of cathodal (c-tDCS) and anodal (a-DCS) transcranial direct current stimulation applied after memory reactivation and extinction in rats.

METHODS

Male Wistar rats were randomly assigned into three groups: one sham group, one anodal tDCS group, and one cathodal tDCS group (500 μA, 20 min). Reconsolidation and extinction of fear memories were evaluated using a contextual fear conditioning.

RESULTS

Our results showed that c-tDCS and a-tDCS after memory reactivation can attenuate mild fear memories. However, only c-tDCS stimulation prevented both fear expression under strong fear learning and fear recovery after a reinstatement protocol without modification of learning rate or extinction retrieval. Nevertheless, the remote memories were resistant to modification through this type of neuromodulation. Our results are discussed considering the interaction between intrinsic excitability promoted by learning and memory retrieval and the electric field applied during tDCS.

CONCLUSION

These results point out some of the boundary conditions influencing the efficacy of tDCS in fear attenuation and open new ways for the development of noninvasive interventions aimed to control fear-related disorders via reconsolidation.

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

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

Effect of the NMDA receptor partial agonist, d-cycloserine, on emotional processing and autobiographical memory

BACKGROUND

Studies suggest that d-cycloserine (DCS) may have antidepressant potential through its interaction with the glycine site of the N-methyl-D-aspartate receptor; however, clinical evidence of DCS's efficacy as a treatment for depression is limited. Other evidence suggests that DCS affects emotional learning which may also be relevant for the treatment of depression and anxiety. The aim of the present investigation was to assess the effect of DCS on emotional processing in healthy volunteers and to further characterise its effects on emotional and autobiographical memory.

METHODS

Forty healthy volunteers were randomly allocated to a single dose of 250 mg DCS or placebo in a double-blind design. Three hours later, participants performed an Emotional Test Battery [including Facial Expression Recognition Task (FERT), Emotional Categorisation Task (ECAT), Emotional Recall Task (EREC), Facial Dot-Probe Task (FDOT) and Emotional Recognition Memory Task (EMEM)] and an Autobiographical Memory Test (AMT). Also, participants performed the FERT, EREC and AMT tasks again after 24 h in order to assess longer lasting effects of a single dose of DCS.

RESULTS

DCS did not significantly affect the FERT, EMEM and FDOT performance but significantly increased emotional memory and classification for positive words v. negative words. Also, DCS enhanced the retrieval of more specific autobiographical memories, and this effect persisted at 24 h.

CONCLUSIONS

These findings support the suggestion that low-dose DCS increases specific autobiographical memory retrieval and positive emotional memory. Such effects make it an intriguing agent for further investigation in clinical depression, which is characterised by decreased autobiographical memory specificity and increased negative bias in memory recall. It also underscores the potential role of DCS as an adjunct to cognitive behavioural therapy in depression.

Prevention of the return of extinguished fear by disrupting the interaction of neuronal nitric oxide synthase with its carboxy-terminal PDZ ligand

Exposure therapy based on the extinction of fear memory is first-line treatment for post-traumatic stress disorder (PTSD). However, fear extinction is relatively easy to learn but difficult to remember, extinguished fear often relapses under a number of circumstances. Here, we report that extinction learning-induced association of neuronal nitric oxide synthase (nNOS) with its carboxy-terminal PDZ ligand (CAPON) in the infralimbic (IL) subregion of medial prefrontal cortex negatively regulates extinction memory and dissociating nNOS-CAPON can prevent the return of extinguished fear in mice. Extinction training significantly increases nNOS-CAPON association in the IL. Disruptors of nNOS-CAPON increase extracellular signal-regulated kinase (ERK) phosphorylation and facilitate the retention of extinction memory in an ERK2-dependent manner. More importantly, dissociating nNOS-CAPON after extinction training enhances long-term potentiation and excitatory synaptic transmission, increases spine density in the IL, and prevents spontaneous recovery, renewal and reinstatement of remote fear of mice. Moreover, nNOS-CAPON disruptors do not affect other types of learning. Thus, nNOS-CAPON can serve as a new target for treating PTSD.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

Many physiologic effects of l-glutamate, the major excitatory neurotransmitter in the mammalian central nervous system, are mediated via signaling by ionotropic glutamate receptors (iGluRs). These ligand-gated ion channels are critical to brain function and are centrally implicated in numerous psychiatric and neurologic disorders. There are different classes of iGluRs with a variety of receptor subtypes in each class that play distinct roles in neuronal functions. The diversity in iGluR subtypes, with their unique functional properties and physiologic roles, has motivated a large number of studies. Our understanding of receptor subtypes has advanced considerably since the first iGluR subunit gene was cloned in 1989, and the research focus has expanded to encompass facets of biology that have been recently discovered and to exploit experimental paradigms made possible by technological advances. Here, we review insights from more than 3 decades of iGluR studies with an emphasis on the progress that has occurred in the past decade. We cover structure, function, pharmacology, roles in neurophysiology, and therapeutic implications for all classes of receptors assembled from the subunits encoded by the 18 ionotropic glutamate receptor genes. SIGNIFICANCE STATEMENT: Glutamate receptors play important roles in virtually all aspects of brain function and are either involved in mediating some clinical features of neurological disease or represent a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of this class of receptors will advance our understanding of many aspects of brain function at molecular, cellular, and system levels and provide new opportunities to treat patients.

Exercise-induced increases in Anandamide and BDNF during extinction consolidation contribute to reduced threat following reinstatement: Preliminary evidence from a randomized controlled trial

INTRODUCTION

We recently demonstrated that moderate-intensity aerobic exercise delivered during the consolidation of fear extinction learning reduced threat expectancy during a test of extinction recall among women with posttraumatic stress disorder (PTSD). These findings suggest that exercise may be a potential candidate for improving the efficacy of exposure-based therapies, which are hypothesized to work via the mechanisms of fear extinction learning. The purpose of this secondary analysis was to examine whether exercise-induced increases in circulating concentrations of candidate biomarkers: endocannabinoids (anandamide [AEA]; 2-arachidonoylglycerol [2-AG], brain-derived neurotrophic factor (BDNF), and homovanillic acid (HVA), mediate the effects of exercise on extinction recall.

METHODS

Participants (N = 35) completed a 3-day fear acquisition (day 1), extinction (day 2), and extinction recall (day 3) protocol, in which participants were randomly assigned to complete either moderate-intensity aerobic exercise (EX) or a light-intensity control (CON) condition following extinction training (day 2). Blood was obtained prior to and following EX or CON. Threat expectancy ratings during tests of extinction recall (i.e., initial fear recall and fear recall following reinstatement) were obtained 24 h following EX or CON. Mediation was tested using linear-mixed effects models and bootstrapping of the indirect effect.

RESULTS

Circulating concentrations of AEA and BDNF (but not 2-AG and HVA) were found to mediate the relationship between moderate-intensity aerobic exercise and reduced threat expectancy ratings following reinstatement (AEA 95% CI: -0.623 to -0.005; BDNF 95% CI: -0.941 to -0.005).

CONCLUSIONS

Exercise-induced increases in peripheral AEA and BDNF appear to play a role in enhancing consolidation of fear extinction learning, thereby leading to reduced threat expectancies following reinstatement among women with PTSD. Future mechanistic research examining these and other biomarkers (e.g., brain-based biomarkers) is warranted.