Fear load: The psychophysiological over-expression of fear as an intermediate phenotype associated with trauma reactions

Impact of Gender on Child and Adolescent PTSD

PURPOSE OF REVIEW

This review examines the recent literature on biological factors that influence sex differences in posttraumatic stress disorder (PTSD) during childhood and adolescence, focusing on neurobiological, hormonal, and genetic factors that may increase risk in girls.

RECENT FINDINGS

More than 60% of children and adolescents are exposed to traumatic events, and many develop PTSD. There is increasing recognition of gender differences in PTSD, with women having double the rates of the disorder compared to men. These gender differences in symptoms and their underlying neurobiology appear to emerge during adolescence, although it is still unclear which biological mechanisms may play key roles in the development of sex difference. The literature on gender effects in children and adolescents is still in the early stages, and more prospective and longitudinal work is needed; however, estrogen appears to play a key role in increasing risk for PTSD in girls, which emerges in adolescence.

Dexamethasone facilitates fear extinction and safety discrimination in PTSD: A placebo-controlled, double-blind study

Psychophysiological hallmarks of posttraumatic stress disorder (PTSD) include exaggerated fear responses, impaired inhibition and extinction of conditioned fear, and decreased discrimination between safety and fear cues. This increased fear load associated with PTSD can be a barrier to effective therapy thus indicating the need for new treatments to reduce fear expression in people with PTSD. One potential biological target for reducing fear expression in PTSD is the hypothalamic-pituitary-adrenal (HPA) axis, which is dysregulated in PTSD. Recent translational rodent studies and cross-sectional clinical studies have shown that dexamethasone administration and the resulting suppression of cortisol in individuals with PTSD leads to a decrease in the fear responses characteristic of PTSD. These data, taken together, suggest that dexamethasone may serve as a novel pharmacologic intervention for heightened fear responses in PTSD. We conducted a double-blind, placebo-controlled trial to test our hypothesis that dexamethasone administration and the concomitant suppression of HPA axis hyperactivity would attenuate fear expression and enhance fear extinction in individuals with PTSD. Study participants (n=62) were recruited from Grady Memorial Hospital in Atlanta, GA. Participants were randomized to receive dexamethasone or placebo prior to fear conditioning and extinction, in a counterbalanced design (treatments separated by a week). Both PTSD- (n=37) and PTSD+ (n=25) participants showed significant startle increases in the presence of the danger signal during placebo and dexamethasone treatments (all p<0.05). However, only PTSD- control participants showed decreases in fear-potentiated startle across extinction blocks during both conditions (p's≤0.001), with PTSD+ participants showing deficits in fear extinction and safety discrimination in the placebo condition. Notably, extinction and discrimination deficits in PTSD+ subjects were markedly reversed with dexamethasone (p<0.001). These data suggest that dexamethasone may serve as a pharmacological agent with which to facilitate fear extinction and discrimination in individuals with PTSD.

The Moderating Effect of Childhood Maltreatment on the Relations Among PTSD Symptoms, Positive Urgency, and Negative Urgency

Childhood maltreatment increases the risk for posttraumatic stress disorder (PTSD) and comorbid substance use disorder (SUD). One pathway by which this occurs is through impaired emotion regulation. Past research has shown that negative urgency, a deficit in the regulation of negative emotions, is strongly related to PTSD in those with comorbid SUD. However, there is minimal research on the relation between positive urgency and PTSD in those with comorbid SUD. The current study investigated the association between childhood maltreatment, positive urgency, negative urgency, and PTSD symptoms among those with SUD. Results suggested that PTSD was associated with negative urgency and positive urgency overall. Childhood maltreatment did not moderate the association between negative urgency and PTSD. Childhood emotional abuse, emotional neglect, and sexual abuse moderated the relation between positive urgency and PTSD (ΔR² = .04 to .10). The association between PTSD and positive urgency was only significant at lower levels of emotional abuse and neglect. Future research should further examine the processing of positive emotions in those with PTSD and comorbid SUD. Findings might inform clinical interventions among populations exposed to childhood maltreatment to reduce or prevent the development of psychopathology.

Repeated trauma exposure does not impair distress reduction during imaginal exposure for posttraumatic stress disorder

BACKGROUND

Based on experimental research on threat extinction, individuals exposed to repeated traumatic events may have impaired outcome in exposure therapy compared to those who have experienced a single trauma (Lang & McTeague, ). This study examined whether repeated trauma exposure predicts smaller changes in self-reported distress during imaginal exposure and worse outcomes for patients with posttraumatic stress disorder (PTSD).

METHODS

Adults (N = 116) with chronic PTSD received up to 10 sessions of prolonged exposure (PE) therapy. Trauma exposure was assessed via interview and number of traumatic events were summed for each participant. To examine reductions in distress during treatment, mean and peak values of distress during imaginal exposure were calculated for the first imaginal session (initial distress activation) and subsequent sessions (between-session change in distress). Change in PTSD symptoms from pre- to posttreatment and follow-up provided an additional index of outcome.

RESULTS

In-session distress during imaginal exposure decreased over the course of treatment. PTSD symptoms also decreased over treatment, with gains being maintained through follow-up. Repeated trauma exposure was not significantly correlated with initial distress activation. Additionally, linear mixed-model analyses showed no significant association between repeated trauma exposure and between-session change in distress or PTSD symptoms.

CONCLUSIONS

Contrary to recent speculation, repeated trauma exposure did not predict less change in self-reported distress during imaginal exposure or worse PTSD outcomes. The bench-to-bedside linkage of threat extinction to exposure therapy is discussed, noting strengths and weaknesses. Patients with repeated trauma exposure show reductions in distress with exposure treatment and benefit from PE as much as patients with single-exposure trauma histories.

Negative appraisals and fear extinction are independently related to PTSD symptoms

BACKGROUND

Considerable research has revealed impaired fear extinction to be a significant predictor of PTSD. Fear extinction is also considered the primary mechanism of exposure therapy, and a critical factor in PTSD recovery. The cognitive theory of PTSD proposes that symptoms persist due to excessive negative appraisals about the trauma and its sequelae. Research has not yet examined the relationship between fear extinction and negative appraisals in PTSD.

METHODS

A cross-sectional sample of participants with PTSD (n =21), and trauma-exposed controls (n =33) underwent a standardized differential fear conditioning and extinction paradigm, with skin conductance response (SCR) amplitude serving as the index of conditioned responses. The Posttraumatic Cognitions Inventory (PTCI) was used to index catastrophic negative appraisals.

RESULTS

Participants with PTSD demonstrated a slower decrease in overall SCR responses during extinction and greater negative appraisals compared to the group. A moderation analysis revealed that both negative trauma-relevant appraisals and fear extinction learning were independently associated with PTSD symptoms, but there was no moderation interaction.

LIMITATIONS

The current study was limited by a modest sample size, leading to the inclusion of participants with subclinical PTSD symptoms. Further, the current study only assessed fear extinction learning; including a second day extinction recall task may show alternative effects.

CONCLUSIONS

These findings indicate that negative appraisals and fear extinction did not interact, but had independent relationships with PTSD symptoms. Here we show for the first time in an experimental framework that negative appraisals and fear extinction play separate roles in PTSD symptoms.

Amygdala Reactivity and Anterior Cingulate Habituation Predict Posttraumatic Stress Disorder Symptom Maintenance After Acute Civilian Trauma

BACKGROUND

Studies suggest that exaggerated amygdala reactivity is a vulnerability factor for posttraumatic stress disorder (PTSD); however, our understanding is limited by a paucity of prospective, longitudinal studies. Recent studies in healthy samples indicate that, relative to reactivity, habituation is a more reliable biomarker of individual differences in amygdala function. We investigated reactivity of the amygdala and cortical areas to repeated threat presentations in a prospective study of PTSD.

METHODS

Participants were recruited from the emergency department of a large level I trauma center within 24 hours of trauma. PTSD symptoms were assessed at baseline and approximately 1, 3, 6, and 12 months after trauma. Growth curve modeling was used to estimate symptom recovery trajectories. Thirty-one individuals participated in functional magnetic resonance imaging around the 1-month assessment, passively viewing fearful and neutral face stimuli. Reactivity (fearful > neutral) and habituation to fearful faces was examined.

RESULTS

Amygdala reactivity, but not habituation, 5 to 12 weeks after trauma was positively associated with the PTSD symptom intercept and predicted symptoms at 12 months after trauma. Habituation in the ventral anterior cingulate cortex was positively associated with the slope of PTSD symptoms, such that decreases in ventral anterior cingulate cortex activation over repeated presentations of fearful stimuli predicted increasing symptoms.

CONCLUSIONS

Findings point to neural signatures of risk for maintaining PTSD symptoms after trauma exposure. Specifically, chronic symptoms were predicted by amygdala hyperreactivity, and poor recovery was predicted by a failure to maintain ventral anterior cingulate cortex activation in response to fearful stimuli. The importance of identifying patients at risk after trauma exposure is discussed.

Elevated C-reactive protein and posttraumatic stress pathology among survivors of the 9/11 World Trade Center attacks

BACKGROUND

Systemic inflammation has emerged as a promising marker and potential mechanism underlying post-traumatic stress disorder (PTSD). The relationship between posttraumatic stress pathology and systemic inflammation has not, however, been consistently replicated and is potentially confounded by comorbid illness or injury, common complications of trauma exposure.

METHODS

We analyzed a large naturalistic cohort sharing a discrete physical and mental health trauma from the destruction of the World Trade Center (WTC) towers on September 11, 2001 (n = 641). We evaluated the relationship between multiple physical and mental health related indices collected through routine evaluations at the WTC Environmental Health Center (WTC EHC), a treatment program for community members exposed to the disaster. C-Reactive Protein (CRP), a marker of systemic inflammation, was examined in relation to scores for PTSD, PTSD symptom clusters (re-experiencing, avoidance, negative cognitions/mood, arousal), depression and anxiety, while controlling for WTC exposures, lower respiratory symptoms, age, sex, BMI and smoking as potential risks or confounders.

RESULTS

CRP was positively associated with PTSD severity (p < 0.001), trending toward association with depression (p = 0.06), but not with anxiety (p = 0.27). CRP was positively associated with re-experiencing (p < 0.001) and avoidance (p < 0.05) symptom clusters, and trended toward associations with negative cognitions/mood (p = 0.06) and arousal (p = 0.08).

CONCLUSIONS

In this large study of the relationship between CRP and posttraumatic stress pathology, we demonstrated an association between systemic inflammation and stress pathology (PTSD; trending with depression), which remained after adjusting for potentially confounding variables. These results contribute to research findings suggesting a salient relationship between inflammation and posttraumatic stress pathology.

Endogenous cortisol reactivity moderates the relationship between fear inhibition to safety signals and posttraumatic stress disorder symptoms

OBJECTIVE

Posttraumatic stress symptoms (PTSS) are commonly associated with impairments in extinguishing fear to signals previously associated with danger, and also with inhibiting fear to safety signals. Previous studies indicate that PTSS are associated with low cortisol activity, and cortisol is shown to facilitate fear extinction. Few studies have examined the influence of cortisol reactivity on fear extinction in PTSS.

METHOD

We used a standardized fear conditioning and extinction paradigm to investigate the relationship between fear extinction and endogenous salivary cortisol activity in participants with high PTSS (n=18), trauma-exposed controls (n=33), and non-trauma-exposed controls (n=27). Skin conductance response (SCR) was used as an index of conditioned responding. Saliva samples were collected at baseline, and 20min post-fear acquisition for basal and reactive cortisol levels, respectively.

RESULTS

PTSS participants demonstrated a slower rate of extinction learning during the early extinction phase. A moderation analysis revealed that cortisol reactivity was a significant moderator between fear inhibition to the safety signal (CS-) during early extinction and PTSS, but not to the threat signal (CS+). Specifically, this interaction was significant in two ways: (1) participants with elevated cortisol reactivity showed lower PTSS as fear inhibition improved; and (2) participants with low cortisol reactivity showed higher PTSS as fear inhibition improved.

CONCLUSION

The findings of the present study show that the relationship between fear inhibition and cortisol reactivity is complex, and suggest that cortisol reactivity shapes safety signal learning in PTSS.

Enhancing Effects of NMDA-Receptor Blockade on Extinction Learning and Related Brain Activation Are Modulated by BMI

A distributed network including prefrontal and hippocampal regions is involved in context-related extinction learning as well as in renewal. Renewal describes the recovery of an extinguished response if the context of extinction differs from the context of recall. Animal studies have demonstrated that prefrontal, but not hippocampal N-methyl-D-aspartate receptor (NMDAR) antagonism disrupted extinction learning and processing of task context. However, human studies of NMDAR in extinction learning are lacking, while NMDAR antagonism yielded contradictory results in other learning tasks. This fMRI study investigated the role of NMDAR for human behavioral and brain activation correlates of extinction and renewal. Healthy volunteers received a single dose of the NMDAR antagonist memantine prior to extinction of previously acquired stimulus-outcome associations presented in either identical or novel contexts. We observed better, and partly faster, extinction learning in participants receiving the NMDAR antagonist compared to placebo. However, memantine did not affect renewal. In both extinction and recall, the memantine group showed a deactivation in extinction-related brain regions, particularly in the prefrontal cortex, while hippocampal activity was increased. This higher hippocampal activation was in turn associated with the participants' body mass index (BMI) and extinction errors. Our results demonstrate potentially dose-related enhancing effects of memantine and highlight involvement of hippocampal NMDAR in context-related extinction learning.

Accessible Neurobehavioral Anger-Related Markers for Vulnerability to Post-Traumatic Stress Symptoms in a Population of Male Soldiers

Identifying vulnerable individuals prone to develop post-traumatic stress symptoms (PTSS) is of paramount importance, especially in populations at high risk for stress exposure such as combat soldiers. While several neural and psychological risk factors are known, no post-traumatic stress disorder (PTSD) biomarker has yet progressed to clinical use. Here we present novel and clinically applicable anger-related neurobehavioral risk markers for military-related PTSS in a large cohort of Israeli soldiers. The psychological, electrophysiological and neural (Simultaneous recording of scalp electroencephalography [EEG] and functional magnetic resonance imaging [fMRI]) reaction to an anger-inducing film were measured prior to advanced military training and PTSS were recorded at 1-year follow-up. Limbic modulation was measured using a novel approach that monitors amygdala modulation using fMRI-inspired EEG, hereafter termed amygdala electrical fingerprint (amyg-EFP). Inter-subject correlation (ISC) analysis on fMRI data indicated that during movie viewing participants' brain activity was synchronized in limbic regions including the amygdala. Self-reported state-anger and amyg-EFP modulation successfully predicted PTSS levels. State-anger significantly accounted for 20% of the variance in PTSS, and amyg-EFP signal modulation significantly accounted for additional 15% of the variance. Our study was limited by the moderate PTSS levels and lack of systematic baseline symptoms assessment. These results suggest that pre-stress neurobehavioral measures of anger may predict risk for later PTSS, pointing to anger-related vulnerability factors that can be measured efficiently and at a low cost before stress exposure. Possible mechanisms underlying the association between the anger response and risk for PTSS are discussed.

Six Years of Research on the National Institute of Mental Health's Research Domain Criteria (RDoC) Initiative: A Systematic Review

Six years have passed since the National Institute of Mental Health (NIMH) in the United States launched the Research Domain Criteria (RDoC) initiative. The RDoC introduces a framework for research on the biology of mental illness that integrates research findings across multiple levels of information. The framework outlines constructs that represent specific quantifiable dimensions of behavior (e.g., responses to acute threat, cognitive control) and corresponding units of analysis that can be used to study the constructs, beginning at the levels of genes, molecules, cells, circuits and physiology, and moving up to behaviors and self-reports. In this systematic review, a literature search was conducted to synthesize empirical research published since the proposal of the framework that incorporated the RDoC. Forty-eight peer-reviewed scholarly articles met eligibility criteria for the review. Studies differed according to whether they analyzed RDoC constructs and units of analysis within vs. between clinically-diagnosed and non-psychiatric samples. The most commonly studied constructs were subsumed within the domains of Negative Valence Systems, Positive Valence Systems and Cognitive Systems, providing initial results which primarily connected genetics, brain circuits and physiology research findings with behavior and self-reports. Prospects for future research adopting the RDoC matrix and utilizing a dimensional approach to studying the biology of mental illness are discussed.

Fear-Potentiated Startle and Fear Extinction in a Sample of Undergraduate Women Exposed to a Campus Mass Shooting

Posttraumatic stress disorder (PTSD) is a common psychological disorder that affects a substantial minority of individuals. Previous research has suggested that PTSD can be partially explained as a disorder of impaired fear inhibition. The current study utilized a previously validated fear acquisition and extinction paradigm in a sample of 75 undergraduate women who were exposed to a campus mass shooting that occurred in 2008. We used a protocol in which conditioned fear was first acquired through the presentation of one colored shape (reinforced conditioned stimulus, CS+) that was paired with an aversive airblast to the larynx (unconditioned stimulus, US) and a different colored shape that was not paired with the airblast (non-reinforced conditioned stimulus, CS-). Fear was extinguished 10 min later through repeated presentations of the CSs without reinforcement. Number of clinically significant posttraumatic stress symptoms (PTSS) immediately following the mass shooting were positively associated with fear-potentiated startle (FPS) to the CS+ and CS- during late periods of acquisition. During early periods of fear extinction, PTSS was positively associated with FPS to the CS+. Results from the current study suggest that PTSS is related to altered fear inhibition and extinction during an FPS paradigm. In line with similar research, women with greater PTSS demonstrated a greater “fear load,” suggesting that these women experienced elevated fear to the CS+ during extinction after conditioned fear was acquired.

Post-Traumatic Stress Disorder: The Relationship Between the Fear Response and Chronic Stress

Post-traumatic stress disorder (PTSD) is a disabling psychiatric condition that can develop following a physical, psychological, or sexual trauma. Despite the growing body of literature examining the psychological and biological factors involved in PTSD psychopathology, specific biomarkers that may improve diagnosis and treatment of PTSD have yet to be identified and validated. This challenge may be attributed to the diverse array of symptoms that individuals with the disorder manifest. Examining the interrelated stress and fear systems allows for a more comprehensive study of these symptoms, and through this approach, which aligns with the research domain criteria (RDoC) framework, neural and psychophysiological measures of PTSD have emerged. In this review, we discuss PTSD neurobiology and treatment within the context of fear and stress network interactions and elucidate the advantages of using an RDoC approach to better understand PTSD with fear conditioning and extinction paradigms.

Posttraumatic stress disorder: A metabolic disorder in disguise?

Posttraumatic stress disorder (PTSD) is a heterogeneous psychiatric disorder that affects individuals exposed to trauma and is highly co-morbid with other adverse health outcomes, including cardiovascular disease and obesity. The unique pathophysiological feature of PTSD is the inability to inhibit fear responses, such that individuals suffering from PTSD re-experience traumatic memories and are unable to control psychophysiological responses to trauma-associated stimuli. However, underlying alterations in sympathetic nervous system activity, neuroendocrine systems, and metabolism associated with PTSD are similar to those present in traditional metabolic disorders, such as obesity and diabetes. The current review highlights existing clinical, translational, and preclinical data that support the notion that underneath the primary indication of impaired fear inhibition, PTSD is itself also a metabolic disorder and proposes altered function of inflammatory responses as a common underlying mechanism. The therapeutic implications of treating PTSD as a whole-body condition are significant, as targeting any underlying biological system whose activity is altered in both PTSD and metabolic disorders, (i.e. HPA axis, sympathetic nervous systems, inflammation) may elicit symptomatic relief in individuals suffering from these whole-body adverse outcomes.

The centrality of fear extinction in linking risk factors to PTSD: A narrative review

Recent prospective studies in emergency services have identified impaired fear extinction learning and memory to be a significant predictor of Posttraumatic Stress Disorder (PTSD), complementing a wealth of cross-sectional evidence of extinction deficits associated with the disorder. Additional fields of research show specific risk factors and biomarkers of the disorder, including candidate genotypes, stress and sex hormones, cognitive factors, and sleep disturbances. Studies in mostly nonclinical populations also reveal that the aforementioned factors are involved in fear extinction learning and memory. Here, we provide a comprehensive narrative review of the literature linking PTSD to these risk factors, and linking these risk factors to impaired fear extinction. On balance, the evidence suggests that fear extinction may play a role in the relationship between risk factors and PTSD. Should this notion hold true, this review carries important implications for the improvement of exposure-based treatments, as well as strategies for the implementation of treatment.

Quantitative Trait Loci and a Novel Genetic Candidate for Fear Learning

Trauma- and stress-related disorders are clinically heterogeneous and associated with substantial genetic risk. Understanding the biological origins of heterogeneity of key intermediate phenotypes such as cognition and emotion can provide novel mechanistic insights into disorder pathogenesis. Performing quantitative genetics in animal models is a tractable strategy for examining both the genetic basis of intermediate phenotypes and functional testing of candidate quantitative traits genes (QTGs). Here, existing and newly collected data were used for collaborative genome-wide mapping of cued fear acquisition and expression in 65 mouse strains from the BXD genetic reference panel. For fear acquisition, we identified a significant locus on chromosome (Chr) 10 and eight suggestive loci on Chr 2, 4, 5, 11, 13, and 15. For fear expression, we identified one significant and another highly suggestive locus on Chr 13, as well as four suggestive loci on Chr 10, 11, and X. Across these loci, 60 putative QTGs were identified. The quantitative trait locus on distal Chr 13 contained a single, highly promising gene at the location of the peak likelihood ratio statistic score. The gene, hyperpolarization-activated cyclic nucleotide-gated channel 1 (Hcn1), regulates neuronal excitability. Validation experiments using behavioral pharmacology revealed that functional Hcn channels in the basolateral amygdala are necessary for conditioned fear acquisition and expression. Hcn1, together with the other candidate QTGs, thus provide new targets for neurobiological and treatment studies of fear learning and trauma- and stress-related disorders.

SIGNIFICANCE STATEMENT

There is a knowledge gap in understanding the genetic contributions to behavioral heterogeneity in typical and atypical populations. Mouse genetic reference panels (GRPs) provide one approach for identifying genetic sources of variation. Here, we identified three loci for conditioned fear acquisition and expression in a mouse GRP. Each locus contained candidate quantitative trait genes (QTGs). One locus had a single QTG, Hcn1 (hyperpolarization-activated cyclic nucleotide-gated channel 1), which has been implicated in neuronal excitability and learning. This discovery was validated using behavioral pharmacology, revealing that Hcn channels in the basolateral amygdala are required for fear acquisition and expression. The study thus identifies novel candidate QTGs that may contribute to variation in emotional learning and highlight the utility of mouse GRPs for the identification of genes underlying complex traits.

Baseline psychophysiological and cortisol reactivity as a predictor of PTSD treatment outcome in virtual reality exposure therapy

Baseline cue-dependent physiological reactivity may serve as an objective measure of posttraumatic stress disorder (PTSD) symptoms. Additionally, prior animal model and psychological studies would suggest that subjects with greatest symptoms at baseline may have the greatest violation of expectancy to danger when undergoing exposure based psychotherapy; thus treatment approaches which enhanced the learning under these conditions would be optimal for those with maximal baseline cue-dependent reactivity. However methods to study this hypothesis objectively are lacking. Virtual reality (VR) methodologies have been successfully employed as an enhanced form of imaginal prolonged exposure therapy for the treatment of PTSD. Our goal was to examine the predictive nature of initial psychophysiological (e.g., startle, skin conductance, heart rate) and stress hormone responses (e.g., cortisol) during presentation of VR-based combat-related stimuli on PTSD treatment outcome. Combat veterans with PTSD underwent 6 weeks of VR exposure therapy combined with either d-cycloserine (DCS), alprazolam (ALP), or placebo (PBO). In the DCS group, startle response to VR scenes prior to initiation of treatment accounted for 76% of the variance in CAPS change scores, p < 0.001, in that higher responses predicted greater changes in symptom severity over time. Additionally, baseline cortisol reactivity was inversely associated with treatment response in the ALP group, p = 0.04. We propose that baseline cue-activated physiological measures will be sensitive to predicting patients' level of response to exposure therapy, in particular in the presence of enhancement (e.g., DCS).

Fear Memory

Fear memory is the best-studied form of memory. It was thoroughly investigated in the past 60 years mostly using two classical conditioning procedures (contextual fear conditioning and fear conditioning to a tone) and one instrumental procedure (one-trial inhibitory avoidance). Fear memory is formed in the hippocampus (contextual conditioning and inhibitory avoidance), in the basolateral amygdala (inhibitory avoidance), and in the lateral amygdala (conditioning to a tone). The circuitry involves, in addition, the pre- and infralimbic ventromedial prefrontal cortex, the central amygdala subnuclei, and the dentate gyrus. Fear learning models, notably inhibitory avoidance, have also been very useful for the analysis of the biochemical mechanisms of memory consolidation as a whole. These studies have capitalized on in vitro observations on long-term potentiation and other kinds of plasticity. The effect of a very large number of drugs on fear learning has been intensively studied, often as a prelude to the investigation of effects on anxiety. The extinction of fear learning involves to an extent a reversal of the flow of information in the mentioned structures and is used in the therapy of posttraumatic stress disorder and fear memories in general.

Situating psychophysiological science within the Research Domain Criteria (RDoC) framework

The Research Domain Criteria (RDoC) reflects a paradigm shift in mental health research aimed at establishing a science of psychopathology that is grounded in neuroscience. In many ways, the RDoC approach to research has been utilized for decades by psychophysiologists who have leveraged a range of biological measures to study variability in psychological processes as a function of individual differences. We highlight the critical role of psychophysiology in the era of RDoC, and briefly review the 13 papers and commentary that form the current special issue.

Psychophysiological science and the research domain criteria: A commentary

The current special issue, devoted to the Research Domain Criteria (RDoC) initiative of the US National Institute of Mental Health, showcases a variety of empirical and review articles that address issues related to this dimensional and multi-method approach to research on mental disorders. Here, we provide an integrative perspective on various aspects of these articles, focused around the primary principles of the RDoC approach and the practical and methodological issues related to conducting RDoC-informed research. The chief point we wish to highlight is that these articles demonstrate the ways in which the field of psychophysiology already thinks along the lines of RDoC in terms of using biobehavioral constructs, looking for convergence among constructs using various methodologies, and utilizing dimensional measurements in studies. In this sense, RDoC is not novel; however, by specifying a formal research platform it provides explicit encouragement and guidance for using such principles in understanding psychiatric phenomena, rather than continuing to focus research efforts on traditional diagnostic categories alone.

An investigation of outcome expectancies as a predictor of treatment response for combat veterans with PTSD: comparison of clinician, self-report, and biological measures

BACKGROUND

Outcome expectancy, or the degree to which a client believes that therapy will result in improvement, is related to improved treatment outcomes for multiple disorders. There is a paucity of research investigating this relation in regards to posttraumatic stress disorder (PTSD). Additionally, the bulk of the research on outcome expectancy and treatment outcomes has relied mostly on self-report outcome measures.

METHODS

The relation between outcome expectancy on self-report measures, clinician-rated measures, and two biological indices (fear-potentiated startle and cortisol reactivity) of PTSD symptoms was explored. The sample included combat veterans (N = 116) treated with virtual reality exposure therapy for PTSD.

RESULTS

Results supported a negative association between outcome expectancy and both self-report and clinician-rated symptoms at the conclusion of treatment, but outcome expectancy was related to the magnitude of change during treatment for self-report measures only. Outcome expectancy was unrelated to biological measures of treatment response.

CONCLUSIONS

These findings suggest that outcome expectancy may be related to patient and clinician perceptions of outcomes, but not biological indices of outcome for PTSD.

Neural correlates of individual differences in fear learning

Variability in fear conditionability is common, and clarity regarding the neural regions responsible for individual differences in fear conditionability could uncover brain-based biomarkers of resilience or vulnerability to trauma-based psychopathologies (e.g., post-traumatic stress disorder). In recent years, neuroimaging work has yielded a detailed understanding of the neural mechanisms underlying fear conditioning common across participants, however only a minority of studies have investigated the brain basis of inter-individual variation in fear learning. Moreover, the majority of these studies have employed small sample sizes (mean n=17; range n=5-27) and all have failed to meet the minimum recommended sample size for functional magnetic resonance imaging (fMRI) studies of individual differences. Here, using fMRI, we analyzed blood-oxygenation level dependent (BOLD) response recorded simultaneously with skin conductance response (SCR) and ratings of unconditioned stimulus (US) expectancy in 49 participants undergoing Pavlovian fear conditioning. On average, participants became conditioned to the conditioned stimulus (CS+; higher US expectancy ratings and SCR for the CS+ compared to the unpaired conditioned stimulus, CS-); the CS+ also robustly increased activation in the bilateral insula. Amygdala activation was revealed from a regression analysis that incorporated individual differences in fear conditionability (i.e., a between-subjects regressor of mean CS+>CS- SCR). By replicating results observed using much smaller sample sizes, the results confirm that variation in amygdala reactivity covaries with individual differences in fear conditionability. The link between behavior (SCR) and brain (amygdala reactivity) may be a putative endophenotype for the acquisition of fear memories.

Norepinephrine and corticosterone in the medial prefrontal cortex and hippocampus predict PTSD-like symptoms in mice

This study measured changes in brain extracellular norepinephrine (NE) and free corticosterone (CORT) levels in a mouse model of post-traumatic stress disorder and related them to hyperarousal and fear memory retention. To this end, microdialysis in the medial prefrontal cortex (mPFC) and the hippocampus (HPC) of male C57BL/6NCrl mice was performed during an acoustic startle response (ASR) and following an electric foot shock (FS), as well as during an ASR and recall of contextual fear (CF) 1 day later. Changes in ASR-stimulated NE levels in the mPFC corresponded to ASR 34 days after FS. Changes in basal and ASR-stimulated extracellular NE levels in the HPC, in contrast, were related to expression of early (day 2) and late (day 34) CF after FS. The increase in extracellular NE levels correlated in a U-shape manner with arousal levels and CF, thus suggesting a non-direct relationship. Stress of different modalities/strength (ASR, FS and CF) caused a similar relative increase in free CORT levels both in the mPFC and the HPC. One day after FS, ASR-induced increases in the CORT content in the mPFC tended to correlate with the FS-potentiated ASR in a U-shape manner. Taken together, these data show that the intracerebral increase in free CORT was likely related to an immediate response to stress, whereas NE neurotransmission in the forebrain predicted arousal and CF 1 month after trauma.