Systematically investigating the role of context on effect replicability in reinstatement of fear in humans.

Context is crucial in guiding behavior in an ever-changing world and contextual information plays a crucial role in associative learning processes. For instance, the return of fear (RoF) after successful extinction, which is used to study the mechanisms underlying relapse phenomena in fear- and stress-related disorders in an experimental model, is known to be context dependent as evident from phenomena such as renewal (contextual change) and reinstatement (re-exposure to an aversive event). Human adaptions of reinstatement paradigms have resulted in mixed findings: CS specific as well as unspecific RoF or unexpected "reinstated" conditioned responding in no reinstatement US control groups. Here, we systematically investigate the role of context (i.e., cue-context compound) on reinstatement-induced RoF in a human differential fear conditioning paradigm using subjective and psychophysiological measures in a large sample (N = 212) including reinstatement and control groups. Overall, response patterns in reinstatement-groups mirrored results from single-cue rodent work. Yet, only generalized, not differential RoF was observed. Remarkably, depending on outcome measure RoF was also observed under identical experimental context conditions without US-re-exposure, underlining effects of contextual change beyond the reinstatement-US and challenging reinstatement research in human subjects and highlight that future reinstatement work should focus on the operationalization of context.

Individual differences in human fear generalization-pattern identification and implications for anxiety disorders.

Previous research indicates that anxiety disorders are characterized by an overgeneralization of conditioned fear as compared with healthy participants. Therefore, fear generalization is considered a key mechanism for the development of anxiety disorders. However, systematic investigations on the variance in fear generalization are lacking. Therefore, the current study aims at identifying distinctive phenotypes of fear generalization among healthy participants. To this end, 1175 participants completed a differential fear conditioning phase followed by a generalization test. To identify patterns of fear generalization, we used a k-means clustering algorithm based on individual arousal generalization gradients. Subsequently, we examined the reliability and validity of the clusters and phenotypical differences between subgroups on the basis of psychometric data and markers of fear expression. Cluster analysis reliably revealed five clusters that systematically differed in mean responses, differentiation between conditioned threat and safety, and linearity of the generalization gradients, though mean response levels accounted for most variance. Remarkably, the patterns of mean responses were already evident during fear acquisition and corresponded most closely to psychometric measures of anxiety traits. The identified clusters reliably described subgroups of healthy individuals with distinct response characteristics in a fear generalization test. Following a dimensional view of psychopathology, these clusters likely delineate risk factors for anxiety disorders. As crucial group characteristics were already evident during fear acquisition, our results emphasize the importance of average fear responses and differentiation between conditioned threat and safety as risk factors for anxiety disorders.

Latency of skin conductance responses across stimulus modalities.

Reproducibility and methodological robustness are of major concern in research today, also with respect to autonomic measures. Quantification of skin conductance responses (SCRs), for instance, relies on response characteristics such as response onset (i.e., latency), which were established more than four decades ago by using paper-pencil methods. Since then, data acquisition has advanced to digital methods, improving sampling rates up to 100,000 samples/second and thereby improving resolution and accuracy. Here, SCR latency as a major characteristic for defining an appropriate response window is revisited by using state-of-the-art equipment. Furthermore, SCR latencies are investigated across different stimulus modalities (tactile, auditory, visual) and with respect to their temporal dynamics over the course of a learning experiment (i.e., fear conditioning). The established response latency criteria were largely confirmed even though results did suggest an even narrower and potential stimulus modality-specific latency criterion. Exploratory analyses investigating individual differences in SCR latencies provided first evidence for a role of sex and cognitive effects (i.e., contingency awareness) while dispositional negativity as well as other personality traits did not affect SCR latencies. Consequently, SCR latencies might have an informative and discriminative value beyond a solely criterial function for defining response windows. The current findings may help to improve the rigor of using SCRs and suggest that SCR latency as a descriptive measure warrants further investigation.

Modulation of defensive reactivity by GLRB allelic variation: converging evidence from an intermediate phenotype approach.

Representing a phylogenetically old and very basic mechanism of inhibitory neurotransmission, glycine receptors have been implicated in the modulation of behavioral components underlying defensive responding toward threat. As one of the first findings being confirmed by genome-wide association studies for the phenotype of panic disorder and agoraphobia, allelic variation in a gene coding for the glycine receptor beta subunit (GLRB) has recently been associated with increased neural fear network activation and enhanced acoustic startle reflexes. On the basis of two independent healthy control samples, we here aimed to further explore the functional significance of the GLRB genotype (rs7688285) by employing an intermediate phenotype approach. We focused on the phenotype of defensive system reactivity across the levels of brain function, structure, and physiology. Converging evidence across both samples was found for increased neurofunctional activation in the (anterior) insular cortex in GLRB risk allele carriers and altered fear conditioning as a function of genotype. The robustness of GLRB effects is demonstrated by consistent findings across different experimental fear conditioning paradigms and recording sites. Altogether, findings provide translational evidence for glycine neurotransmission as a modulator of the brain's evolutionary old dynamic defensive system and provide further support for a strong, biologically plausible candidate intermediate phenotype of defensive reactivity. As such, glycine-dependent neurotransmission may open up new avenues for mechanistic research on the etiopathogenesis of fear and anxiety disorders.

GLRB allelic variation associated with agoraphobic cognitions, increased startle response and fear network activation: a potential neurogenetic pathway to panic disorder.

The molecular genetics of panic disorder (PD) with and without agoraphobia (AG) are still largely unknown and progress is hampered by small sample sizes. We therefore performed a genome-wide association study with a dimensional, PD/AG-related anxiety phenotype based on the Agoraphobia Cognition Questionnaire (ACQ) in a sample of 1370 healthy German volunteers of the CRC TRR58 MEGA study wave 1. A genome-wide significant association was found between ACQ and single non-coding nucleotide variants of the GLRB gene (rs78726293, P=3.3 × 10-8; rs191260602, P=3.9 × 10-8). We followed up on this finding in a larger dimensional ACQ sample (N=2547) and in independent samples with a dichotomous AG phenotype based on the Symptoms Checklist (SCL-90; N=3845) and a case-control sample with the categorical phenotype PD/AG (Ncombined =1012) obtaining highly significant P-values also for GLRB single-nucleotide variants rs17035816 (P=3.8 × 10-4) and rs7688285 (P=7.6 × 10-5). GLRB gene expression was found to be modulated by rs7688285 in brain tissue, as well as cell culture. Analyses of intermediate PD/AG phenotypes demonstrated increased startle reflex and increased fear network, as well as general sensory activation by GLRB risk gene variants rs78726293, rs191260602, rs17035816 and rs7688285. Partial Glrb knockout mice demonstrated an agoraphobic phenotype. In conjunction with the clinical observation that rare coding GLRB gene mutations are associated with the neurological disorder hyperekplexia characterized by a generalized startle reaction and agoraphobic behavior, our data provide evidence that non-coding, although functional GLRB gene polymorphisms may predispose to PD by increasing startle response and agoraphobic cognitions.

Adversity-induced relapse of fear: neural mechanisms and implications for relapse prevention from a study on experimentally induced return-of-fear following fear conditioning and extinction.

The efficacy of current treatments for anxiety disorders is limited by high relapse rates. Relapse of anxiety disorders and addiction can be triggered by exposure to life adversity, but the underlying mechanisms remain unexplored. Seventy-six healthy adults were a priori selected for the presence or absence of adverse experiences during childhood (CA) and recent past (RA; that is, past 12 months). Participants underwent fear conditioning (day 1) and fear extinction and experimental return-of-fear (ROF) induction through reinstatement (a model for adversity-induced relapse; day 2). Ratings, autonomic (skin conductance response) and neuronal activation measures (functional magnetic resonance imaging (fMRI)) were acquired. Individuals exposed to RA showed a generalized (that is, not CS- specific) fear recall and ROF, whereas unexposed individuals showed differential (that is, CS+ specific) fear recall and ROF on an autonomic level despite no group differences during fear acquisition and extinction learning. These group differences in ROF were accompanied by corresponding activation differences in brain areas known to be involved in fear processing and differentiability/generalization of ROF (that is, hippocampus). In addition, dimensional measures of RA, CA and lifetime adversity were negatively correlated with differential skin conductance responses (SCRs) during ROF and hippocampal activation. As discriminating signals of danger and safety, as well as a tendency for overgeneralization, are core features in clinically anxious populations, these deficits may specifically contribute to relapse risk following exposure to adversity, in particular to recent adversity. Hence, our results may provide first and novel insights into the possible mechanisms mediating enhanced relapse risk following exposure to (recent) adversity, which may guide the development of effective pre- and intervention programs.

Deficient inhibitory processing in trait anxiety: Evidence from context-dependent fear learning, extinction recall and renewal.

BACKGROUND: Impaired fear inhibition has been described as a hallmark of pathological anxiety. We aimed at further characterizing the relation between fear inhibition and anxiety by extending previous work to contextual safety stimuli as well as to dimensional scores of trait anxiety in a large sample. METHODS: We employed a validated paradigm for context-dependent fear acquisition/extinction (day 1) and retrieval/expression (day 2) in 377 healthy individuals. This large sample size allowed the employment of a dimensional rather than binary approach with respect to individual differences in trait anxiety. RESULTS: We observed a positive correlation on day 1 between trait anxiety with all CSs that possess an inherent inhibitory component, conveyed either by reliable non-reinforcement of a specific CS in a dangerous context (safe cue) or by the context itself (i.e., safe context). No correlation however was observed for a CS that possesses excitatory (threatening) properties only. These results were observed during fear learning (day 1) for US expectancy and fear ratings but not for SCRs. No such pattern was evident during fear and extinction retrieval/expression (day 2). CONCLUSION: We provide further evidence that high trait anxiety is associated with the inability to take immediate advantage of environmental safety cues (cued and contextual), which might represent a promising trans-diagnostic marker for different anxiety disorders. Consequently, the incorporation of methods to optimize inhibitory learning in current cognitive behavioral therapy (CBT) treatments might open up a promising avenue for precision medicine in anxiety disorders. LIMITATIONS: We did not include patients diagnosed with anxiety disorders.

A review on experimental and clinical genetic associations studies on fear conditioning, extinction and cognitive-behavioral treatment.

Fear conditioning and extinction represent basic forms of associative learning with considerable clinical relevance and have been implicated in the pathogenesis of anxiety disorders. There is considerable inter-individual variation in the ability to acquire and extinguish conditioned fear reactions and the study of genetic variants has recently become a focus of research. In this review, we give an overview of the existing genetic association studies on human fear conditioning and extinction in healthy individuals and of related studies on cognitive-behavioral treatment (CBT) and exposure, as well as pathology development after trauma. Variation in the serotonin transporter (5HTT) and the catechol-o-methyltransferase (COMT) genes has consistently been associated with effects in pre-clinical and clinical studies. Interesting new findings, which however require further replication, have been reported for genetic variation in the dopamine transporter (DAT1) and the pituitary adenylate cyclase 1 receptor (ADCYAP1R1) genes, whereas the current picture is inconsistent for variation in the brain-derived neurotrophic factor (BDNF) gene. We end with a discussion of the findings and their limitations, as well as future directions that we hope will aid the field to develop further.