Prefrontal mechanisms of fear reduction after threat offset

Medial anterior prefrontal cortex stimulation downregulates implicit reactions to threats and prevents the return of fear

Downregulating emotional overreactions toward threats is fundamental for developing treatments for anxiety and post-traumatic disorders. The prefrontal cortex (PFC) is critical for top-down modulatory processes, and despite previous studies adopting repetitive transcranial magnetic stimulation (rTMS) over this region provided encouraging results in enhancing extinction, no studies have hitherto explored the effects of stimulating the medial anterior PFC (aPFC, encompassing the Brodmann area 10) on threat memory and generalization. Here we showed that rTMS over the aPFC applied before threat memory retrieval immediately decreases implicit reactions to learned and novel stimuli in humans. These effects enduringly persisted 1 week later in the absence of rTMS. No effects were detected on explicit recognition. Critically, rTMS over the aPFC resulted in a more pronounced reduction of defensive responses compared to rTMS targeting the dorsolateral PFC. These findings reveal a previously unexplored prefrontal region, the modulation of which can efficiently and durably inhibit implicit reactions to learned threats. This represents a significant advancement toward the long-term deactivation of exaggerated responses to threats.

Optimised Multi-Channel Transcranial Direct Current Stimulation (MtDCS) Reveals Differential Involvement of the Right-Ventrolateral Prefrontal Cortex (rVLPFC) and Insular Complex in those Predisposed to Aberrant Experiences

Research has shown a prominent role for cortical hyperexcitability underlying aberrant perceptions, hallucinations, and distortions in human conscious experience - even in neurotypical groups. The rVLPFC has been identified as an important structure in mediating cognitive affective states / feeling conscious states. The current study examined the involvement of the rVLPFC in mediating cognitive affective states in those predisposed to aberrant experiences in the neurotypical population. Participants completed two trait-based measures: (i) the Cortical Hyperexcitability Index_II (CHi_II, a proxy measure of cortical hyperexcitability) and (ii) two factors from the Cambridge Depersonalisation Scale (CDS). An optimised 7-channel MtDCS montage for stimulation conditions (Anodal, Cathodal and Sham) was created targeting the rVLPFC in a single-blind study. At the end of each stimulation session, participants completed a body-threat task (BTAB) while skin conductance responses (SCRs) and psychological responses were recorded. Participants with signs of increasing cortical hyperexcitability showed significant suppression of SCRs in the Cathodal stimulation relative to the Anodal and sSham conditions. Those high on the trait-based measures of depersonalisation-like experiences failed to show reliable effects. Collectively, the findings suggest that baseline brain states can mediate the effects of neurostimulation which would be missed via sample level averaging and without appropriate measures for stratifying individual differences.

Recent advances in studying brain-behavior interactions using functional imaging: The primary startle response pathway and its affective modulation in humans

The startle response is a cross-species defensive reflex that is considered a key tool for cross-species translational emotion research. While the neural pathway mediating (affective) startle modulation has been extensively studied in rodents, human work on brain-behavior interactions has lagged in the past due to technical challenges, which have only recently been overcome through non-invasive simultaneous EMG-fMRI assessments. We illustrate key paradigms and methodological tools for startle response assessment in rodents and humans and review evidence for primary and modulatory neural circuits underlying startle responses and their affective modulation in humans. Based on this, we suggest a refined and integrative model for primary and modulatory startle response pathways in humans concluding that there is strong evidence from human work on the neurobiological pathway underlying the primary startle response while evidence for the modulatory pathway is still sparse. In addition, we provide methodological considerations to guide future work and provide an outlook on new and exciting perspectives enabled through technical and theoretical advances outlined in this work.

Conscious expectancy rather than associative strength elicits brain activity during single-cue fear conditioning

The neurocognitive processes underlying Pavlovian conditioning in humans are still largely debated. The conventional view is that conditioned responses (CRs) emerge automatically as a function of the contingencies between a conditioned stimulus (CS) and an unconditioned stimulus (US). As such, the associative strength model asserts that the frequency or amplitude of CRs reflects the strength of the CS-US associations. Alternatively, the expectation model asserts that the presentation of the CS triggers conscious expectancy of the US, which is responsible for the production of CRs. The present study tested the hypothesis that there are dissociable brain networks related to the expectancy and associative strength theories using a single-cue fear conditioning paradigm with a pseudo-random intermittent reinforcement schedule during functional magnetic resonance imaging. Participants' (n = 21) trial-by-trial expectations of receiving shock displayed a significant linear effect consistent with the expectation model. We also found a positive linear relationship between the expectancy model and activity in frontoparietal brain areas including the dorsolateral prefrontal cortex (PFC) and dorsomedial PFC. While an exploratory analysis found a linear relationship consistent with the associated strength model in the insula and early visual cortex, our primary results are consistent with the view that conscious expectancy contributes to CRs.

Fear conditioning and extinction learning in the mood and anxiety disorders spectrum - Associations with the outcome of cognitive behavior therapy

In the current study, we test for the specificity of deficits in fear acquisition and extinction for the anxiety disorders spectrum. We compared fear acquisition and fear extinction learning between a group of patients with either an anxiety disorder (n = 93) or depression (n = 103) attending for treatment in our outpatient center and a sample of healthy control participants (n = 60). To assess the specificity of the predictive validity of extinction learning and safety learning for the outcome of exposure-based treatments, patients additionally underwent disorder-specific cognitive behavior therapy (CBT). We found only very little evidence for differences in safety or extinction learning between healthy controls and patients with anxiety-disorders or depression using both a group-based categorical analytic approach, as well as a trans-diagnostic, dimensional analytic approach. On the contrary, for anxiety patients only, more favorable extinction learning and more favorable safety learning was associated with more favorable treatment outcome. In sum, this specific prediction of treatment outcome in anxiety patients confirms and extends current theoretical models of exposure-based treatments for anxiety disorders, but does not support the notion of general extinction learning deficits in the anxiety disorders spectrum.

Postural freezing relates to startle potentiation in a human fear-conditioning paradigm

Freezing to impending threat is a core defensive response. It has been studied primarily using fear conditioning in non-human animals, thwarting advances in translational human anxiety research that has used other indices, such as skin conductance responses. Here we examine postural freezing as a human conditioning index for translational anxiety research. We employed a mixed cued/contextual fear-conditioning paradigm where one context signals the occurrence of the US upon the presentation of the CS, and another context signals that the CS is not followed by the US. Critically, during the following generalization phase, the CS is presented in a third and novel context. We show that human freezing is highly sensitive to fear conditioning, generalizes to ambiguous contexts, and amplifies with threat imminence. Intriguingly, stronger parasympathetically driven freezing under threat, but not sympathetically mediated skin conductance, predicts subsequent startle magnitude. These results demonstrate that humans show fear-conditioned animal-like freezing responses, known to aid in active preparation for unexpected attack, and that freezing captures real-life anxiety expression. Conditioned freezing offers a promising new, non-invasive, and continuous, readout for human fear conditioning, paving the way for future translational studies into human fear and anxiety.

Human defensive freezing: Associations with hair cortisol and trait anxiety

The anticipation of threat facilitates innate defensive behaviours including freezing reactions. Freezing in humans is characterised by reductions in body sway and heart rate. Limited evidence suggests that individual differences in freezing reactions are associated with predictors of anxiety-related psychopathology including trait anxiety and hypothalamic-pituitary-adrenal (HPA) axis activity. However, previous human studies focused on acutely circulating cortisol levels, leaving the link between freezing and more stable, individual trait markers of HPA axis activity unclear. We investigated whether individual differences in anticipatory freezing reactions are predicted by accumulated hair cortisol concentrations (HCC) and trait anxiety, in a well-powered mixed sample of police recruits at the start of the police training, and age, sex and education matched controls (total N = 419, mean age = 24, N_women = 106, N_{police recruits} = 337). Freezing-related reactions were assessed with posturographic and heart rate measurements during an active shooting task under threat of shock. The anticipation of threat of shock elicited the expected reductions in body sway and heart rate, indicative of human freezing. Individual differences in threat-related reductions in body sway, but not heart rate, were related to lower HCC and higher trait anxiety. The observed links between postural freezing and predictors of anxiety-related psychopathology suggest the potential value of defensive freezing as a somatic marker for individual differences in stress-vulnerability and resilience. DATA AVAILABILITY: The datasets analysed during the current study are available from the corresponding authors upon reasonable request.

Anterior prefrontal brain activity during emotion control predicts resilience to post-traumatic stress symptoms

Regulating social emotional actions is essential for coping with life stressors and is associated with control by the anterior prefrontal cortex (aPFC) over the amygdala. However, it remains unclear to what extent prefrontal emotion regulation capacities contribute to resilience against developing post-traumatic stress disorder (PTSD) symptoms. Here, 185 police recruits who experienced their core trauma in the line of duty participated in a prospective longitudinal study. Pre- and post-trauma, they performed a well-established functional magnetic resonance imaging (fMRI) approach-avoidance task, mapping impulsive and controlled emotional actions. Higher baseline aPFC, dorsal and medial frontal pole activity was related to lower PTSD symptoms after trauma exposure. aPFC activity predicted symptom development over and above self-reported and behavioural measures. Trauma exposure, but not trauma symptoms, predicted amygdala activation at follow-up. These findings suggest that prefrontal emotion regulation activity predicts increased resilience against developing post-traumatic stress symptoms and may provide fruitful starting points for prediction and intervention studies.

Attentive immobility in the face of inevitable distal threat-Startle potentiation and fear bradycardia as an index of emotion and attention

During fear conditioning, a cue (CS) signals an inevitable distal threat (US) and evokes a conditioned response that can be described as attentive immobility (freezing). The organism remains motionless and monitors the source of danger while startle responses are potentiated, indicating a state of defensive hypervigilance. Although in animals vagally mediated fear bradycardia is also reliably observed under such circumstances, results are mixed in human fear conditioning. Using a single-cue fear conditioning and extinction protocol, we tested cardiac reactivity and startle potentiation indexing low-level defensive strategies in a fear-conditioned (n = 40; paired presentations of CS and US) compared with a non-conditioned control group (n = 40; unpaired presentations of CS and US). Additionally, we assessed shock expectancy ratings on a trial-by-trial basis indexing declarative knowledge of the previous contingencies. Half of each group underwent extinction under sham or active transcutaneous vagus nerve stimulation (tVNS), serving as additional proof of concept. We found stronger cardiac deceleration during CS presentation in the fear learning relative to the control group. This learned fear bradycardia was positively correlated with conditioned startle potentiation but not with declarative knowledge of CS-US contingencies. TVNS abolished differences in heart rate changes between both groups and removed the significant correlation between late cardiac deceleration and startle potentiation in the fear learning group. Results suggest, fear-conditioned cues evoke attentive immobility in humans, characterized by cardiac deceleration and startle potentiation. Such defensive response pattern is elicited by cues predicting inevitable distal threat and resembles conditioned fear responses observed in rodents.

Latent class growth analyses reveal overrepresentation of dysfunctional fear conditioning trajectories in patients with anxiety-related disorders compared to controls

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

Individual differences in costly fearful avoidance and the relation to psychophysiology

Excessive avoidance behaviour is a cardinal symptom of anxiety disorders. Avoidance is not only associated with the benefits of avoiding threats, but also with the costs of missing out on rewards upon exploration. Psychological and psychophysiological mechanisms contributing to these costly avoidance decisions in prospect of mixed outcomes remain unclear. We developed a novel Fearful Avoidance Task (FAT) that resembles characteristics of real-life approach-avoidance conflicts, enabling to disentangle reward and threat effects. Using the FAT, we investigated individual differences in avoidance behaviour and anticipatory psychophysiological states (i.e. startle reflex and skin conductance) in a relatively large sample of 343 (78 females) participants. Avoidance under acute threat of shock depends on a trade-off between perceived reward and threat. Both increased startle and skin conductance in the absence of threat of shock emerged as predictors of increased avoidance (potentially indicative of fear generalization). Increased avoidance was also associated with female sex and trait anxiety, dependent on reward and threat levels. Our findings highlight distinct possible predictors of heightened avoidance and add to mechanistic understanding of how individual propensity for costly avoidance may emerge. Distinct avoidance typologies based on differential reward and threat sensitivities may have different mechanistic origins and thereby could benefit from different treatment strategies.

Learning dynamics of electrophysiological brain signals during human fear conditioning

Electrophysiological studies in rodents allow recording neural activity during threats with high temporal and spatial precision. Although fMRI has helped translate insights about the anatomy of underlying brain circuits to humans, the temporal dynamics of neural fear processes remain opaque and require EEG. To date, studies on electrophysiological brain signals in humans have helped to elucidate underlying perceptual and attentional processes, but have widely ignored how fear memory traces evolve over time. The low signal-to-noise ratio of EEG demands aggregations across high numbers of trials, which will wash out transient neurobiological processes that are induced by learning and prone to habituation. Here, our goal was to unravel the plasticity and temporal emergence of EEG responses during fear conditioning. To this end, we developed a new sequential-set fear conditioning paradigm that comprises three successive acquisition and extinction phases, each with a novel CS+/CS- set. Each set consists of two different neutral faces on different background colors which serve as CS+ and CS-, respectively. Thereby, this design provides sufficient trials for EEG analyses while tripling the relative amount of trials that tap into more transient neurobiological processes. Consistent with prior studies on ERP components, data-driven topographic EEG analyses revealed that ERP amplitudes were potentiated during time periods from 33-60 ms, 108-200 ms, and 468-820 ms indicating that fear conditioning prioritizes early sensory processing in the brain, but also facilitates neural responding during later attentional and evaluative stages. Importantly, averaging across the three CS+/CS- sets allowed us to probe the temporal evolution of neural processes: Responses during each of the three time windows gradually increased from early to late fear conditioning, while long-latency (460-730 ms) electrocortical responses diminished throughout fear extinction. Our novel paradigm demonstrates how short-, mid-, and long-latency EEG responses change during fear conditioning and extinction, findings that enlighten the learning curve of neurophysiological responses to threat in humans.

Neural Dynamics of Shooting Decisions and the Switch from Freeze to Fight

Real-life shooting decisions typically occur under acute threat and require fast switching between vigilant situational assessment and immediate fight-or-flight actions. Recent studies suggested that freezing facilitates action preparation and decision-making but the neurocognitive mechanisms remain unclear. We applied functional magnetic resonance imaging, posturographic and autonomic measurements while participants performed a shooting task under threat of shock. Two independent studies, in unselected civilians (N = 22) and police recruits (N = 54), revealed that preparation for shooting decisions under threat is associated with postural freezing, bradycardia, midbrain activity (including the periaqueductal gray-PAG) and PAG-amygdala connectivity. Crucially, stronger activity in the midbrain/PAG during this preparatory stage of freezing predicted faster subsequent accurate shooting. Finally, the switch from preparation to active shooting was associated with tachycardia, perigenual anterior cingulate cortex (pgACC) activity and pgACC-amygdala connectivity. These findings suggest that threat-anticipatory midbrain activity centred around the PAG supports decision-making by facilitating action preparation and highlight the role of the pgACC when switching from preparation to action. These results translate animal models of the neural switch from freeze-to-action. In addition, they reveal a core neural circuit for shooting performance under threat and provide empirical evidence for the role of defensive reactions such as freezing in subsequent action decision-making.

No Time-Dependent Effects of Psychosocial Stress on Fear Contextualization and Generalization: A Randomized-Controlled Study With Healthy Participants

The formation of context-dependent fear memories (fear contextualization) can aid the recognition of danger in new, similar, situations. Overgeneralization of fear is often seen as hallmark of anxiety and trauma-related disorders. In this randomized-controlled study, we investigated whether exposure to a psychosocial stressor influences retention of fear contextualization and generalization in a time-dependent manner. The Trier Social Stress Test was used to induce psychosocial stress. Healthy male participants (n = 117) were randomly divided into three experimental groups that were subjected to the acquisition phase of the Fear Generalization Task: (1) without stress, (2) immediately after acute stress, or (3) 2 h after acute stress. In this task, a male with neutral facial expression (conditioned stimuli) was depicted in two different contexts that modulated the conditioned stimuli-unconditioned stimuli (=shock) association (threat, safe). Salivary alpha-amylase and cortisol levels were measured throughout the experiment. After a 24-h delay, context-dependency of fear memory was investigated with an unannounced memory test consisting of the threat and safe contexts alternated with a novel context (the generalization context). Multilevel analyses revealed that participants showed increased fear-potentiated startle responses to the conditioned stimuli in the threat compared to the safe context, at the end of the acquisition phase, indicating adequate fear contextualization. Directly after acquisition, there were no time-dependent effects of psychosocial stress on fear contextualization. Context-dependency of fear memories was retained 24 h later, as fear-potentiated startle responding was modulated by context (threat > safe or novel). At that time, the context-dependency of fear memories was also not influenced by the early or late effects of the endogenous stress response during acquisition. These results with experimental stress deviate in some aspects from those earlier obtained with exogenous hydrocortisone administration, suggesting a distinct role for stress mediators other than cortisol.

The uncertain brain: A co-ordinate based meta-analysis of the neural signatures supporting uncertainty during different contexts

Uncertainty is often inevitable in everyday life and can be both stressful and exciting. Given its relevance to psychopathology and wellbeing, recent research has begun to address the brain basis of uncertainty. In the current review we examined whether there are discrete and shared neural signatures for different uncertain contexts. From the literature we identified three broad categories of uncertainty currently empirically studied using functional MRI (fMRI): basic threat and reward uncertainty, decision-making under uncertainty, and associative learning under uncertainty. We examined the neural basis of each category by using a coordinate based meta-analysis, where brain activation foci from previously published fMRI experiments were drawn together (1998-2017; 87 studies). The analyses revealed shared and discrete patterns of neural activation for uncertainty, such as the insula and amygdala, depending on the category. Such findings will have relevance for researchers attempting to conceptualise uncertainty, as well as clinical researchers examining the neural basis of uncertainty in relation to psychopathology.

The Basolateral Amygdala Is Essential for Rapid Escape: A Human and Rodent Study

Rodent research delineates how the basolateral amygdala (BLA) and central amygdala (CeA) control defensive behaviors, but translation of these findings to humans is needed. Here, we compare humans with natural-selective bilateral BLA lesions to rats with a chemogenetically silenced BLA. We find, across species, an essential role for the BLA in the selection of active escape over passive freezing during exposure to imminent yet escapable threat (Timm). In response to Timm, BLA-damaged humans showed increased startle potentiation and BLA-silenced rats demonstrated increased startle potentiation, freezing, and reduced escape behavior as compared to controls. Neuroimaging in humans suggested that the BLA reduces passive defensive responses by inhibiting the brainstem via the CeA. Indeed, Timm conditioning potentiated BLA projections onto an inhibitory CeA pathway, and pharmacological activation of this pathway rescued deficient Timm responses in BLA-silenced rats. Our data reveal how the BLA, via the CeA, adaptively regulates escape behavior from imminent threat and that this mechanism is evolutionary conserved across rodents and humans.

Effects of testosterone administration on threat and escape anticipation in the orbitofrontal cortex

Recent evidence suggests that the steroid hormone testosterone can decrease the functional coupling between orbitofrontal cortex (OFC) and amygdala. Theoretically this decoupling has been linked to a testosterone-driven increase of goal-directed behaviour in case of threat, but this has never been studied directly. Therefore, we placed twenty-two women in dynamically changing situations of escapable and inescapable threat after a within-subject placebo controlled testosterone administration. Using functional magnetic resonance imaging (fMRI) we provide evidence that testosterone activates the left lateral OFC (LOFC) in preparation of active goal-directed escape and decouples this OFC area from a subcortical threat system including the central-medial amygdala, hypothalamus and periaqueductal gray. This LOFC decoupling was specific to threatening situations, a point that was further emphasized by an absence of such decoupling in a second experiment focused on resting-state connectivity. These results not only confirm that testosterone administration decouples the LOFC from the subcortical threat system, but also show that this is specifically the case in response to acute threat, and ultimately leads to an increase in LOFC activity when the participant prepares a goal-directed action to escape. Together these results for the first time provide a detailed understanding of functional brain alterations induced by testosterone under threat conditions, and corroborate and extend the view that testosterone prepares the brain for goal-directed action in case of threat.

Augmentation of Fear Extinction by Transcranial Direct Current Stimulation (tDCS)

Although posttraumatic stress disorder (PTSD; DSM-V 309.82) and anxiety disorders (DSM-V 300.xx) are widely spread mental disorders, the effectiveness of their therapy is still unsatisfying. Non-invasive brain-stimulation techniques like transcranial direct current stimulation (tDCS) might be an option to improve extinction learning, which is a main functional factor of exposure-based therapy for anxiety disorders. To examine this hypothesis, we used a fear conditioning paradigm with female faces as conditioned stimuli (CS) and a 95-dB female scream as unconditioned stimulus (UCS). We aimed to perform a tDCS of the ventromedial prefrontal cortex (vmPFC), which is mainly involved in the control of extinction-processes. Therefore, we applied two 4 × 4 cm electrodes approximately at the EEG-positions F7 and F8 and used a direct current of 1.5 mA. The 20-min stimulation was started during a 10-min break between acquisition and extinction and went on overall extinction-trials. The healthy participants were randomly assigned in two double-blinded process into two sham stimulation and two verum stimulation groups with opposite current flow directions. To measure the fear reactions, we used skin conductance responses (SCR) and subjective ratings. We performed a generalized estimating equations model for the SCR to assess the impact of tDCS and current flow direction on extinction processes for all subjects that showed a successful conditioning (N = 84). The results indicate that tDCS accelerates early extinction processes with a significantly faster loss of CS+/CS– discrimination. The discrimination loss was driven by a significant decrease in reaction toward the CS+ as well as an increase in reaction toward the CS– in the tDCS verum groups, whereas the sham groups showed no significant reaction changes during this period. Therefore, we assume that tDCS of the vmPFC can be used to enhance early extinction processes successfully. But before it should be tested in a clinical context further investigation is needed to assess the reason for the reaction increase on CS–. If this negative side effect can be avoided, tDCS may be a tool to improve exposure-based anxiety therapies.

How acute stress may enhance subsequent memory for threat stimuli outside the focus of attention: DLPFC-amygdala decoupling

Stress-related disorders, e.g., anxiety and depression, are characterized by decreased top-down control for distracting information, as well as a memory bias for threatening information. However, it is unclear how acute stress biases mnemonic encoding and leads to prioritized storage of threat-related information even if outside the focus of attention. In the current study, healthy adults (N = 53, all male) were randomly assigned to stress induction using the socially evaluated cold-pressor test (SECPT) or a control condition. Participants performed a task in which they were required to identify a target letter within a string of letters that were either identical to the target and thereby facilitating detection (low distractor load) or mixed with other letters to complicate the search (high load). Either a fearful or neutral face was presented on the background, outside the focus of attention. Twenty-four hours later, participants were asked to perform a surprise recognition memory test for those background faces. Stress induction resulted in increased cortisol and negative subjective mood ratings. Stress did not affect visual search performance, however, participants in the stress group showed stronger memory compared to the control group for fearful faces in the low attentional load condition. Critically, the stress induced memory bias was accompanied by decoupling between amygdala and DLFPC during encoding, which may represent a mechanism for decreased ability to filter task-irrelevant threatening background information. The current study provides a potential neural account for how stress can produce a negative memory bias for threatening information even if presented outside the focus of attention. Despite of an adaptive advantage for survival, such tendencies may ultimately also lead to generalized fear, a possibility requiring additional investigation.

How Human Amygdala and Bed Nucleus of the Stria Terminalis May Drive Distinct Defensive Responses

The ability to adaptively regulate responses to the proximity of potential danger is critical to survival and imbalance in this system may contribute to psychopathology. The bed nucleus of the stria terminalis (BNST) is implicated in defensive responding during uncertain threat anticipation whereas the amygdala may drive responding upon more acute danger. This functional dissociation between the BNST and amygdala is however controversial, and human evidence scarce. Here we used data from two independent functional magnetic resonance imaging studies [n = 108 males and n = 70 (45 females)] to probe how coordination between the BNST and amygdala may regulate responses during shock anticipation and actual shock confrontation. In a subset of participants from Sample 2 (n = 48) we demonstrate that anticipation and confrontation evoke bradycardic and tachycardic responses, respectively. Further, we show that in each sample when going from shock anticipation to the moment of shock confrontation neural activity shifted from a region anatomically consistent with the BNST toward the amygdala. Comparisons of functional connectivity during threat processing showed overlapping yet also consistently divergent functional connectivity profiles for the BNST and amygdala. Finally, childhood maltreatment levels predicted amygdala, but not BNST, hyperactivity during shock anticipation. Our results support an evolutionary conserved, defensive distance-dependent dynamic balance between BNST and amygdala activity. Shifts in this balance may enable shifts in defensive reactions via the demonstrated differential functional connectivity. Our results indicate that early life stress may tip the neural balance toward acute threat responding and via that route predispose for affective disorder.SIGNIFICANCE STATEMENT Previously proposed differential contributions of the BNST and amygdala to fear and anxiety have been recently debated. Despite the significance of understanding their contributions to defensive reactions, there is a paucity of human studies that directly compared these regions on activity and connectivity during threat processing. We show strong evidence for a dissociable role of the BNST and amygdala in threat processing by demonstrating in two large participant samples that they show a distinct temporal signature of threat responding as well as a discriminable pattern of functional connections and differential sensitivity to early life threat.

Proximity alert! Distance related cuneus activation in military veterans with anger and aggression problems

Problems involving anger and aggression are common after military deployment, and may involve abnormal responses to threat. This study therefore investigated effects on neural activation related to threat and escapability among veterans with deployment experience. Twenty-seven male veterans with anger and aggression problems (Anger group) and 30 Control veterans performed a virtual predator-task during fMRI measurement. In this task, threat and proximity were manipulated. The distance of cues determined their possibility for escape. Cues signaled impending attack by zooming in towards the participant. If Threat cues, but not Safe cues, reached the participants without being halted by a button press, an aversive noise (105dB scream) was presented. In both the Threat and the Safe condition, closer proximity of the virtual predator resulted in stronger activation in the cuneus in the Anger versus Control group. The results suggest that anger and aggression problems are related to a generalized sensitivity to proximity rather than preparatory processes related to task-contingent aversive stimuli. Anger and aggression problems in natural, dynamically changing environments may be related to an overall heightened vigilance, which is non-adaptively driven by proximity.

Don't fear 'fear conditioning': Methodological considerations for the design and analysis of studies on human fear acquisition, extinction, and return of fear

The so-called 'replicability crisis' has sparked methodological discussions in many areas of science in general, and in psychology in particular. This has led to recent endeavours to promote the transparency, rigour, and ultimately, replicability of research. Originating from this zeitgeist, the challenge to discuss critical issues on terminology, design, methods, and analysis considerations in fear conditioning research is taken up by this work, which involved representatives from fourteen of the major human fear conditioning laboratories in Europe. This compendium is intended to provide a basis for the development of a common procedural and terminology framework for the field of human fear conditioning. Whenever possible, we give general recommendations. When this is not feasible, we provide evidence-based guidance for methodological decisions on study design, outcome measures, and analyses. Importantly, this work is also intended to raise awareness and initiate discussions on crucial questions with respect to data collection, processing, statistical analyses, the impact of subtle procedural changes, and data reporting specifically tailored to the research on fear conditioning.

The role of automatic defensive responses in the development of posttraumatic stress symptoms in police recruits: protocol of a prospective study

Background: Control over automatic tendencies is often compromised in challenging situations when people fall back on automatic defensive reactions, such as freeze-fight-flight responses. Stress-induced lack of control over automatic defensive responses constitutes a problem endemic to high-risk professions, such as the police. Difficulties controlling automatic defensive responses may not only impair split-second decisions under threat, but also increase the risk for and persistence of posttraumatic stress disorder (PTSD) symptoms. However, the significance of these automatic defensive responses in the development and maintenance of trauma-related symptoms remains unclear due to a shortage of large-scale prospective studies. Objective: The 'Police-in-Action' study is conducted to investigate the role of automatic defensive responses in the development and maintenance of PTSD symptomatology after trauma exposure. Methods: In this prospective study, 340 police recruits from the Dutch Police Academy are tested before (wave 1; pre-exposure) and after (wave 2; post-exposure) their first emergency aid experiences as police officers. The two waves of data assessment are separated by approximately 15 months. To control for unspecific time effects, a well-matched control group of civilians (n = 85) is also tested twice, approximately 15 months apart, but without being frequently exposed to potentially traumatic events. Main outcomes are associations between (changes in) behavioural, psychophysiological, endocrine and neural markers of automatic defensive responses and development of trauma-related symptoms after trauma exposure in police recruits. Discussion: This prospective study in a large group of primary responders enables us to distinguish predisposing from acquired neurobiological abnormalities in automatic defensive responses, associated with the development of trauma-related symptoms. Identifying neurobiological correlates of (vulnerability for) trauma-related psychopathology may greatly improve screening for individuals at risk for developing PTSD symptomatology and offer valuable targets for (early preventive) interventions for PTSD.

Transcranial Direct Current Stimulation (tDCS) of the Right Inferior Frontal Gyrus Attenuates Skin Conductance Responses to Unpredictable Threat Conditions

Patients with panic and post-traumatic stress disorders seem to show increased psychophysiological reactions to conditions of unpredictable (U) threat, which has been discussed as a neurobiological marker of elevated levels of sustained fear in these disorders. Interestingly, a recent study found that the right inferior frontal gyrus (rIFG) is correlated to the successful regulation of sustained fear during U threat. Therefore this study aimed to examine the potential use of non-invasive brain stimulation to foster the rIFG by means of anodal transcranial direct current stimulation (tDCS) in order to reduce psychophysiological reactions to U threat. Twenty six participants were randomly assigned into an anodal and sham stimulation group in a double-blinded manner. Anodal and cathodal electrodes (7 * 5 cm) were positioned right frontal to target the rIFG. Stimulation intensity was I = 2 mA applied for 20 min during a task including U threat conditions (NPU-task). The effects of the NPU paradigm were measured by assessing the emotional startle modulation and the skin conductance response (SCR) at the outset of the different conditions. We found a significant interaction effect of condition × tDCS for the SCR (F_(2,48) = 6.3, p < 0.01) without main effects of condition and tDCS. Post hoc tests revealed that the increase in SCR from neutral (N) to U condition was significantly reduced in verum compared to the sham tDCS group (t₍₂₄₎ = 3.84, p < 0.001). Our results emphasize the causal role of rIFG for emotional regulation and the potential use of tDCS to reduce apprehension during U threat conditions and therefore as a treatment for anxiety disorders.

Human fear acquisition deficits in relation to genetic variants of the corticotropin-releasing hormone receptor 1 and the serotonin transporter--revisited

We recently showed that a genetic polymorphism (rs878886) in the human corticotropin-releasing hormone receptor 1 (CRHR1) is associated with reduced fear-conditioned responses to a threat cue. This is a potentially important finding considering that the failure to acquire fear contingencies can leave an individual in a maladaptive state of more generalized anxiety. Consistent with that idea, the CRHR1-dependent fear acquisition deficit translated into heightened contextual anxiety when taking genetic variability within the serotonin transporter long polymorphic region (5-HTTLPR) into account. To replicate our previous findings, we conducted a replication study in 224 healthy medication-free human subjects using the exact same cue and context virtual reality fear-conditioning procedure as in study by Heitland et al. (2013). In the replication study, consistent with the original findings, CRHR1 rs878886 G-allele carriers showed reduced acquisition of cue-specific fear-conditioned responses compared with C/C homozygotes. Also, in this larger sample the cue acquisition deficit of G-allele carriers translated into heightened contextual anxiety, even independent of 5-HTT gene variation. In contrast to our earlier findings, there was an additional interaction effect of CRHR1 rs878886 and the triallelic 5-HTTLPR/rs25531 variant on cued fear acquisition. In summary, this study replicated the initially reported association of the CRHR1 rs878886 G-allele with cued fear acquisition deficits, albeit with a different pattern of results regarding the interaction with 5-HTT variation. This further supports the notion that the human corticotropin-releasing hormone plays a role in the acquisition of fears.

A Stress-Induced Shift From Trace to Delay Conditioning Depends on the Mineralocorticoid Receptor

BACKGROUND

Fear learning in stressful situations is highly adaptive for survival by steering behavior in subsequent situations, but fear learning can become disproportionate in vulnerable individuals. Despite the potential clinical significance, the mechanism by which stress modulates fear learning is poorly understood. Memory theories state that stress can cause a shift away from more controlled processing depending on the hippocampus toward more reflexive processing supported by the amygdala and striatum. This shift may be mediated by activation of the mineralocorticoid receptor (MR) for cortisol. We investigated how stress shifts processes underlying cognitively demanding learning versus less demanding fear learning using a combined trace and delay fear conditioning paradigm.

METHODS

In a pharmacological functional magnetic resonance imaging study, we tested 101 healthy men probing the effects of stress (socially evaluated cold pressor vs. control procedure) and MR-availability (400 mg spironolactone vs. placebo) in a randomized, placebo-controlled, full-factorial, between-subjects design.

RESULTS

Effective stress induction and successful conditioning were confirmed by subjective, physiologic, and somatic data. In line with a stress-induced shift, stress enhanced later recall of delay compared with trace conditioning in the MR-available groups as indexed by skin conductance responses. During learning, this was accompanied by a stress-induced reduction of learning-related hippocampal activity for trace conditioning. The stress-induced shift in fear and neural processing was absent in the MR-blocked groups.

CONCLUSIONS

Our results are in line with a stress-induced shift in fear learning, mediated by the MR, resulting in a dominance of cognitively less demanding amygdala-based learning, which might be particularly prominent in individuals with high MR sensitivity.

Dissociated neural effects of cortisol depending on threat escapability

Evolution has provided us with a highly flexible neuroendocrine threat system which, depending on threat imminence, switches between active escape and passive freezing. Cortisol, the "stress-hormone", is thought to play an important role in both fear behaviors, but the exact mechanisms are not understood. Using pharmacological functional magnetic resonance imaging we investigated how cortisol modulates the brain's fear systems when humans are under virtual-predator attack. We show dissociated neural effects of cortisol depending on whether escape from threat is possible. During inescapable threat cortisol reduces fear-related midbrain activity, whereas in anticipation of active escape cortisol boosts activity in the frontal salience network (insula and anterior cingulate cortex), which is involved in autonomic control, visceral perception and motivated action. Our findings suggest that cortisol adjusts the human neural threat system from passive fear to active escape, which illuminates the hormone's crucial role in the adaptive flexibility of fear behaviors.

Psychopathology research in the RDoC era: Unanswered questions and the importance of the psychophysiological unit of analysis

The NIMH Research Domain Criteria (RDoC) initiative seeks to re-conceptualize psychopathology by identifying transdiagnostic constructs that reflect core mechanisms of psychopathology. Although the RDoC framework has been discussed in many prior papers, there are several methodological and conceptual points that have yet to be fully specified. For example, little discussion exists on the importance of distinguishing each construct's nomological network and linking it to risk for psychopathology. It has also been unclear the extent to which RDoC constructs (within and across systems) should relate to one another and how these associations may differ as a function of developmental period. These are important questions as we enter the RDoC era and psychophysiological measures represent an exciting tool to address these issues. In this paper, we discuss the currently un- (or under-)specified aspects of the RDoC initiative and highlight the advantages of the psychophysiological 'unit of analysis.' We also briefly review existing psychophysiological studies, within the positive and negative valence systems, that exemplify the RDoC approach and make recommendations for how future studies can help the field progress in this mission.

Dorsomedial Prefrontal Cortex Mediates the Impact of Serotonin Transporter Linked Polymorphic Region Genotype on Anticipatory Threat Reactions

BACKGROUND

Excessive anticipatory reactions to potential future adversity are observed across a range of anxiety disorders, but the neurogenetic mechanisms driving interindividual differences are largely unknown. We aimed to discover and validate a gene-brain-behavior pathway by linking presumed genetic risk for anxiety-related psychopathology, key neural activity involved in anxious anticipation, and resulting aversive emotional states.

METHODS

The functional neuroanatomy of aversive anticipation was probed through functional magnetic resonance imaging in two independent samples of healthy subjects (n = 99 and n = 69), and we studied the influence of genetic variance in the serotonin transporter linked polymorphic region (5-HTTLPR). Skin conductance and startle data served as objective psychophysiological indices of the intensity of individuals' anticipatory responses to potential threat.

RESULTS

Threat cues signaling risk of future electrical shock activated the dorsomedial prefrontal cortex (dmPFC), anterior insula, bed nucleus of the stria terminalis, thalamus, and midbrain consistently across both samples. Threat-related dmPFC activation was enhanced in 5-HTTLPR short allele carriers in sample 1 and this effect was validated in sample 2. Critically, we show that this region mediates the increase in anticipatory psychophysiological reactions in short allele carriers indexed by skin conductance (experiment 1) and startle reactions (experiment 2).

CONCLUSIONS

The converging results from these experiments demonstrate that innate 5-HTTLPR linked variation in dmPFC activity predicts psychophysiological responsivity to pending threats. Our results reveal a neurogenetic pathway mediating interindividual variability in anticipatory responses to threat and yield a novel mechanistic account for previously reported associations between genetic variability in serotonin transporter function and stress-related psychopathology.

Controllability modulates the neural response to predictable but not unpredictable threat in humans

Stress resilience is mediated, in part, by our ability to predict and control threats within our environment. Therefore, determining the neural mechanisms that regulate the emotional response to predictable and controllable threats may provide important new insight into the processes that mediate resilience to emotional dysfunction and guide the future development of interventions for anxiety disorders. To better understand the effect of predictability and controllability on threat-related brain activity in humans, two groups of healthy volunteers participated in a yoked Pavlovian fear conditioning study during functional magnetic resonance imaging (fMRI). Threat predictability was manipulated by presenting an aversive unconditioned stimulus (UCS) that was either preceded by a conditioned stimulus (i.e., predictable) or by presenting the UCS alone (i.e., unpredictable). Similar to animal model research that has employed yoked fear conditioning procedures, one group (controllable condition; CC), but not the other group (uncontrollable condition; UC) was able to terminate the UCS. The fMRI signal response within the dorsolateral prefrontal cortex (PFC), dorsomedial PFC, ventromedial PFC, and posterior cingulate was diminished during predictable compared to unpredictable threat (i.e., UCS). In addition, threat-related activity within the ventromedial PFC and bilateral hippocampus was diminished only to threats that were both predictable and controllable. These findings provide insight into how threat predictability and controllability affects the activity of brain regions (i.e., ventromedial PFC and hippocampus) involved in emotion regulation, and may have important implications for better understanding neural processes that mediate emotional resilience to stress.

Impaired acquisition of classically conditioned fear-potentiated startle reflexes in humans with focal bilateral basolateral amygdala damage

Based on studies in rodents, the basolateral amygdala (BLA) is considered a key site for experience-dependent neural plasticity underlying the acquisition of conditioned fear responses. In humans, very few studies exist of subjects with selective amygdala lesions and those studies have only implicated the amygdala more broadly leaving the role of amygdala sub-regions underexplored. We tested a rare sample of subjects (N = 4) with unprecedented focal bilateral BLA lesions due to a genetic condition called Urbach-Wiethe disease. In a classical delay fear conditioning experiment, these subjects showed impaired acquisition of conditioned fear relative to a group of matched control subjects (N = 10) as measured by fear-potentiation of the defensive eye-blink startle reflex. After the experiment, the BLA-damaged cases showed normal declarative memory of the conditioned association. Our findings provide new evidence that the human BLA is essential to drive fast classically conditioned defensive reflexes.

The impact of cue learning, trait anxiety and genetic variation in the serotonin 1A receptor on contextual fear

In everyday life, aversive events are usually associated with certain predictive cues. Normally, the acquisition of these contingencies enables organisms to appropriately respond to threat. Presence of a threat cue clearly signals 'danger', whereas absence of such cues signals a period of 'safety'. Failure to identify threat cues may lead to chronic states of anxious apprehension in the context in which the threat has been imminent, which may be instrumental in the pathogenesis of anxiety disorders. In this study, existing data from 150 healthy volunteers in a cue and context virtual reality fear conditioning paradigm were reanalyzed. The aim was to further characterize the impact of cue acquisition and trait anxiety, and of a single nucleotide polymorphism in the serotonin 1A receptor gene (5-HTR1A, rs6295), on cued fear and contextual anxiety before and after fear contingencies were explicitly introduced. Fear conditioned responding was quantified with fear potentiation of the eyeblink startle reflex and subjective fear ratings. First, we replicated previous findings that the inability to identify danger cues during acquisition leads to heightened anxious apprehension in the threat context. Second, in subjects who did not identify the danger cue initially, contextual fear was associated with trait anxiety after the contingencies were explicitly instructed. Third, genetic variability within 5-HTR1A (rs6295) was associated with contextual fear independent of awareness or trait anxiety. These findings confirm that failure to acquire cue contingencies impacts contextual fear responding, in association with trait anxiety. The observed 5-HTR1A effect is in line with models of anxiety, but needs further replication.

No impact of deep brain stimulation on fear-potentiated startle in obsessive-compulsive disorder

Deep brain stimulation (DBS) of the ventral internal capsule is effective in treating therapy refractory obsessive-compulsive disorder (OCD). Given the close proximity of the stimulation site to the stria terminalis (BNST), we hypothesized that the striking decrease in anxiety symptoms following DBS could be the result of the modulation of contextual anxiety. However, the effect of DBS in this region on contextual anxiety is as of yet unknown. Thus, the current study investigated the effect of DBS on contextual anxiety in an experimental threat of shock paradigm. Eight patients with DBS treatment for severe OCD were tested in a double-blind crossover design with randomly assigned 2-week periods of active and sham stimulation. DBS resulted in significant decrease of obsessive-compulsive symptoms, anxiety, and depression. However, even though the threat manipulation resulted in a clear context-potentiated startle effect, none of the parameters derived from the startle recordings was modulated by the DBS. This suggests that DBS in the ventral internal capsule is effective in treating anxiety symptoms of OCD without modulating the startle circuitry. We hypothesize that the anxiety symptoms present in OCD are likely distinct from the pathological brain circuits in defensive states of other anxiety disorders.

The amygdala mediates the emotional modulation of threat-elicited skin conductance response

The ability to respond adaptively to threats in a changing environment is an important emotional function. The amygdala is a critical component of the neural circuit that mediates many emotion-related processes, and thus likely plays an important role in modulating the peripheral emotional response to threat. However, prior research has largely focused on the amygdala's response to stimuli that signal impending threat, giving less attention to the amygdala's response to the threat itself. From a functional perspective, however, it is the response to the threat itself that is most biologically relevant. Thus, understanding the factors that influence the amygdala's response to threat is critical for a complete understanding of adaptive emotional processes. Therefore, we used functional MRI to investigate factors (i.e., valence and arousal of co-occurring visual stimuli) that influence the amygdala's response to threat (loud white noise). We also assessed whether changes in amygdala activity varied with the peripheral expression of emotion (indexed via skin conductance response; SCR). The results showed that threat-elicited amygdala activation varied with the arousal, not valence, of emotional images. More specifically, threat-elicited amygdala activation was larger to the threat when presented during high-arousal (i.e., negative and positive) versus low-arousal (i.e., neutral) images. Further, the threat-elicited amygdala response was positively correlated with threat-elicited SCR. These findings indicate the amygdala's response to threat is modified by the nature (e.g., arousal) of other stimuli in the environment. In turn, the amygdala appears to mediate important aspects of the peripheral emotional response to threat.

The BDNF Val66Met polymorphism modulates the generalization of cued fear responses to a novel context

Brain-derived neurotrophic factor (BDNF) has a crucial role in activity-dependent synaptic plasticity and learning and memory. The human functional single-nucleotide BDNF rs6265 (Val66Met) polymorphism has been found to be associated with alteration in neural BDNF release and function correlating with altered emotional behavior. Here, we investigated for the first time the hypothesis that this polymorphism in humans modulates the context dependency of conditioned fear responses. Applying a new paradigm examining generalization of cued fear across contexts, 70 participants stratified for BDNF Val66Met polymorphism were guided through two virtual offices (context) in which briefly illuminated blue and yellow lights served as cues. In the fear context, one light (conditioned stimulus, CS+) but not the other light (CS-) was associated with an electric shock (unconditioned stimulus, US). In the safety context, both lights were presented too, but no US was delivered. During the test phase, lights were presented again both in learning contexts and in a novel generalization context without any US. All participants showed clear fear conditioning to the CS+ in the fear context as indicated by potentiation of startle responses and reports of fear. No fear reactions were found for the CS+ in the safety context. Importantly, generalization of fear responses indicated by the potentiation of startle response to the CS+ compared with the CS- in the novel context was evident only in the Met-carrying group. These are the first results to provide evidence in humans that BDNF modulates the generalization of fear responses. Such context-dependent generalization processes might predispose Met carriers for affective and anxiety disorders.

Conditioned fear in low- and high-anxious rats is differentially regulated by cortical subcortical and midbrain 5-HT(1A) receptors

Interactions between the prelimbic cortex and the basolateral amygdala underlie fear memory processing, mostly through acquiring and consolidating the learning of a conditioned fear. More recently, studies highlighted the role of the dorsal periaqueductal gray (DPAG) in the modulation of learning fear responses. In addition, extensive data in the literature have signaled the importance of serotonin (5-HT) on fear and anxiety. In the present study, the role of 5-HT neurotransmission of the prelimbic cortex, basolateral amygdala or the DPAG on the unconditioned and conditioned fear responses in rats previously selected as low- (LA) or high-anxious (HA) were assessed through local infusions of 5-HT itself (10nmol/0.2μl) or the selective 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT - 0.3μg/0.2μl). Behavioral analysis was conducted using the fear-potentiated startle (FPS) procedure. Dependent variables recorded were the latency and amplitude of the unconditioned startle response and FPS. Our findings suggest that, on the prelimbic cortex, 5-HT modulates the expression of conditioned fear response in HA rats and this modulation is dependent on 5-HT1A receptors. This is not true, however, for the basolateral amygdala or the DPAG. In these regions LA but not HA rats were susceptible to the anxiolytic-like effect of 5-HT1A receptor activation. It is thought that the expression of conditioned fear in HA subjects may be dependent on other 5-HT receptors, as the 5-HT1B subtype, and/or changes in other systems such as the GABA and glutamate neurotransmitters. These results increase our understanding of the rostrocaudal influence of 5-HT on the unconditioned and conditioned fear responses in LA and HA subjects and, to some extent, are in disagreement with the theoretical current that emphasizes the role of 5-HT on anxiety, mainly at the subcortical and midbrain levels.

Psychophysiology in the study of psychological trauma: where are we now and where do we need to be?

Posttraumatic stress disorder (PTSD) is a major public health concern, which has been seeing increased recent attention partly due to the wars in Iraq and Afghanistan. Historically, research attempting to understand the etiology and treatment of PTSD has made frequent use of psychophysiological measures of arousal as they provide a number of advantages in providing objective, non-self-report outcomes that are closely related to proposed neurobiological mechanisms and provide opportunity for cross-species translation. Further, the ongoing shift in classification of psychiatric illness based on symptom clusters to specific biological, physiological, and behavioral constructs, as outlined in the US National Institute of Mental Health (NIMH) Research Domain Criteria project (RDoC), promises that psychophysiological research will continue to play a prominent role in research on trauma-related illnesses. This review focuses on the current state of the knowledge regarding psychophysiological measures and PTSD with a focus on physiological markers associated with current PTSD symptoms, as well as markers of constructs thought to be relevant to PTSD symptomatology (safety signal learning, fear extinction), and psychophysiological markers of risk for developing PTSD following trauma. Future directions and issues for the psychophysiological study of trauma including traumatic brain injury (TBI), treatment outcome studies, and new wearable physiological monitoring technologies are also discussed.

Alpha absolute power measurement in panic disorder with agoraphobia patients

BACKGROUND

Panic attacks are thought to be a result from a dysfunctional coordination of cortical and brainstem sensory information leading to heightened amygdala activity with subsequent neuroendocrine, autonomic and behavioral activation. Prefrontal areas may be responsible for inhibitory top-down control processes and alpha synchronization seems to reflect this modulation. The objective of this study was to measure frontal absolute alpha-power with qEEG in 24 subjects with panic disorder and agoraphobia (PDA) compared to 21 healthy controls.

METHODS

qEEG data were acquired while participants watched a computer simulation, consisting of moments classified as "high anxiety"(HAM) and "low anxiety" (LAM). qEEG data were also acquired during two rest conditions, before and after the computer simulation display.

RESULTS

We observed a higher absolute alpha-power in controls when compared to the PDA patients while watching the computer simulation. The main finding was an interaction between the moment and group factors on frontal cortex. Our findings suggest that the decreased alpha-power in the frontal cortex for the PDA group may reflect a state of high excitability.

CONCLUSIONS

Our results suggest a possible deficiency in top-down control processes of anxiety reflected by a low absolute alpha-power in the PDA group while watching the computer simulation and they highlight that prefrontal regions and frontal region nearby the temporal area are recruited during the exposure to anxiogenic stimuli.

Human fear acquisition deficits in relation to genetic variants of the corticotropin releasing hormone receptor 1 and the serotonin transporter

The ability to identify predictors of aversive events allows organisms to appropriately respond to these events, and failure to acquire these fear contingencies can lead to maladaptive contextual anxiety. Recently, preclinical studies demonstrated that the corticotropin-releasing factor and serotonin systems are interactively involved in adaptive fear acquisition. Here, 150 healthy medication-free human subjects completed a cue and context fear conditioning procedure in a virtual reality environment. Fear potentiation of the eyeblink startle reflex (FPS) was measured to assess both uninstructed fear acquisition and instructed fear expression. All participants were genotyped for polymorphisms located within regulatory regions of the corticotropin releasing hormone receptor 1 (CRHR1 - rs878886) and the serotonin transporter (5HTTLPR). These polymorphisms have previously been linked to panic disorder and anxious symptomology and personality, respectively. G-allele carriers of CRHR1 (rs878886) showed no acquisition of fear conditioned responses (FPS) to the threat cue in the uninstructed phase, whereas fear acquisition was present in C/C homozygotes. Moreover, carrying the risk alleles of both rs878886 (G-allele) and 5HTTLPR (short allele) was associated with increased FPS to the threat context during this phase. After explicit instructions regarding the threat contingency were given, the cue FPS and context FPS normalized in all genotype groups. The present results indicate that genetic variability in the corticotropin-releasing hormone receptor 1, especially in interaction with the 5HTTLPR, is involved in the acquisition of fear in humans. This translates prior animal findings to the human realm.

Pain, decisions, and actions: a motivational perspective

Because pain signals potential harm to the organism, it immediately attracts attention and motivates decisions and action. However, pain is also subject to motivations—an aspect that has led to considerable changes in our understanding of (chronic) pain over the recent years. The relationship between pain and motivational states is therefore clearly bidirectional. This review provides an overview on behavioral and neuroimaging studies investigating motivational aspects of pain. We highlight recent insights into the modulation of pain through fear and social factors, summarize findings on the role of pain in fear conditioning, avoidance learning and goal conflicts and discuss evidence on pain-related cognitive interference and motivational aspects of pain relief.

Global decrease of serotonin-1A receptor binding after electroconvulsive therapy in major depression measured by PET

Electroconvulsive therapy (ECT) is a potent therapy in severe treatment-refractory depression. Although commonly applied in psychiatric clinical routine since decades, the exact neurobiological mechanism regarding its efficacy remains unclear. Results from preclinical and clinical studies emphasize a crucial involvement of the serotonin-1A receptor (5-HT(1A)) in the mode of action of antidepressant treatment. This includes associations between treatment response and changes in 5-HT(1A) function and density by antidepressants. Further, alterations of the 5-HT(1A) receptor are consistently reported in depression. To elucidate the effect of ECT on 5-HT(1A) receptor binding, 12 subjects with severe treatment-resistant major depression underwent three positron emission tomography (PET) measurements using the highly selective radioligand [carbonyl-(11)C]WAY100635, twice before (test-retest variability) and once after 10.08±2.35 ECT sessions. Ten patients (~83%) were responders to ECT. The voxel-wise comparison of the 5-HT(1A) receptor binding (BP(ND)) before and after ECT revealed a widespread reduction in cortical and subcortical regions (P<0.05 corrected), except for the occipital cortex and the cerebellum. Strongest reductions were found in regions consistently reported to be altered in major depression and involved in emotion regulation, such as the subgenual part of the anterior cingulate cortex (-27.5%), the orbitofrontal cortex (-30.1%), the amygdala (-31.8%), the hippocampus (-30.6%) and the insula (-28.9%). No significant change was found in the raphe nuclei. There was no significant difference in receptor binding in any region comparing the first two PET scans conducted before ECT. This PET study proposes a global involvement of the postsynaptic 5-HT(1A) receptor binding in the effect of ECT.

Reduced fear-recognition sensitivity following acute buprenorphine administration in healthy volunteers

In rodents, the endogenous opioid system has been implicated in emotion regulation, and in the reduction of fear in particular. In humans, while there is evidence that the opioid antagonist naloxone acutely enhances the acquisition of conditioned fear, there are no corresponding data on the effect of opioid agonists in moderating responses to fear. We investigated whether a single 0.2mg administration of the mu-opioid agonist buprenorphine would decrease fear sensitivity with an emotion-recognition paradigm. Healthy human subjects participated in a randomized placebo-controlled within-subject design, in which they performed a dynamic emotion recognition task 120min after administration of buprenorphine and placebo. In the recognition task, basic emotional expressions were morphed between their full expression and neutral in 2% steps, and presented as dynamic video-clips with final frames of different emotional intensity for each trial, which allows for a fine-grained measurement of emotion sensitivity. Additionally, visual analog scales were used to investigate acute effects of buprenorphine on mood. Compared to placebo, buprenorphine resulted in a significant reduction in the sensitivity for recognizing fearful facial expressions exclusively. Our data demonstrate, for the first time in humans, that acute up-regulation of the opioid system reduces fear recognition sensitivity. Moreover, the absence of an effect of buprenorphine on mood provides evidence of a direct influence of opioids upon the core fear system in the human brain.

Neurobiological mechanisms underlying the blocking effect in aversive learning

Current theories of classical conditioning assume that learning depends on the predictive relationship between events, not just on their temporal contiguity. Here we employ the classic experiment substantiating this reasoning-the blocking paradigm-in combination with functional magnetic resonance imaging (fMRI) to investigate whether human amygdala responses in aversive learning conform to these assumptions. In accordance with blocking, we demonstrate that significantly stronger behavioral and amygdala responses are evoked by conditioned stimuli that are predictive of the unconditioned stimulus than by conditioned stimuli that have received the same pairing with the unconditioned stimulus, yet have no predictive value. When studying the development of this effect, we not only observed that it was related to the strength of previous conditioned responses, but also that predictive compared with nonpredictive conditioned stimuli received more overt attention, as measured by fMRI-concurrent eye tracking, and that this went along with enhanced amygdala responses. We furthermore observed that prefrontal regions play a role in the development of the blocking effect: ventromedial prefrontal cortex (subgenual anterior cingulate) only exhibited responses when conditioned stimuli had to be established as nonpredictive for an outcome, whereas dorsolateral prefrontal cortex also showed responses when conditioned stimuli had to be established as predictive. Most importantly, dorsolateral prefrontal cortex connectivity to amygdala flexibly switched between positive and negative coupling, depending on the requirements posed by predictive relationships. Together, our findings highlight the role of predictive value in explaining amygdala responses and identify mechanisms that shape these responses in human fear conditioning.

Failure to extinguish fear and genetic variability in the human cannabinoid receptor 1

Failure to extinguish fear can lead to persevering anxiety and has been postulated as an important mechanism in the pathogenesis of human anxiety disorders. In animals, it is well documented that the endogenous cannabinoid system has a pivotal role in the successful extinction of fear, most importantly through the cannabinoid receptor 1. However, no human studies have reported a translation of this preclinical evidence yet. Healthy medication-free human subjects (N=150) underwent a fear conditioning and extinction procedure in a virtual reality environment. Fear potentiation of the eyeblink startle reflex was measured to assess fear-conditioned responding, and subjective fear ratings were collected. Participants were genotyped for two polymorphisms located within the promoter region (rs2180619) and the coding region (rs1049353) of cannabinoid receptor 1. As predicted from the preclinical literature, acquisition and expression of conditioned fear did not differ between genotypes. Crucially, whereas both homozygote (G/G, N=23) and heterozygote (A/G, N=68) G-allele carriers of rs2180619 displayed robust extinction of fear, extinction of fear-potentiated startle was absent in A/A homozygotes (N=51). Additionally, this resistance to extinguish fear left A/A carriers of rs2180619 with significantly higher levels of fear-potentiated startle at the end of the extinction training. No effects of rs1049353 genotype were observed regarding fear acquisition and extinction. These results suggest for the first time involvement of the human endocannabinoid system in fear extinction. Implications are that genetic variability in this system may underlie individual differences in anxiety, rendering cannabinoid receptor 1 a potential target for novel pharmacological treatments of anxiety disorders.

Identification of neuronal loci involved with displays of affective aggression in NC900 mice

Aggression is a complex behavior that is essential for survival. Of the various forms of aggression, impulsive violent displays without prior planning or deliberation are referred to as affective aggression. Affective aggression is thought to be caused by aberrant perceptions of, and consequent responses to, threat. Understanding the neuronal networks that regulate affective aggression is pivotal to development of novel approaches to treat chronic affective aggression. Here, we provide a detailed anatomical map of neuronal activity in the forebrain of two inbred lines of mice that were selected for low (NC100) and high (NC900) affective aggression. Attack behavior was induced in male NC900 mice by exposure to an unfamiliar male in a novel environment. Forebrain maps of c-Fos+ nuclei, which are surrogates for neuronal activity during behavior, were then generated and analyzed. NC100 males rarely exhibited affective aggression in response to the same stimulus, thus their forebrain c-Fos maps were utilized to identify unique patterns of neuronal activity in NC900s. Quantitative results indicated robust differences in the distribution patterns and densities of c-Fos+ nuclei in distinct thalamic, subthalamic, and amygdaloid nuclei, together with unique patterns of neuronal activity in the nucleus accumbens and the frontal cortices. Our findings implicate these areas as foci regulating differential behavioral responses to an unfamiliar male in NC900 mice when expressing affective aggression. Based on the highly conserved patterns of connections and organization of neuronal limbic structures from mice to humans, we speculate that neuronal activities in analogous networks may be disrupted in humans prone to maladaptive affective aggression.

Effects of anxiolytic treatment on potentiated startle during aversive image anticipation

OBJECTIVE

Heightened anticipation of future events has been characterized as a feature of certain anxiety disorders. In functional magnetic resonance imaging studies, anticipation of fearful/threatening images has been shown to robustly activate the insular cortex and amygdala in healthy subjects, in subjects with high trait anxiety, and in some with anxiety disorders. Blood oxygenation level dependent activation in response to negative image anticipation is also sensitive to anxiolytic treatment, suggesting that image anticipation probes anxiety systems. It is not clear, however, if behavioral responses to image anticipation are also sensitive to anxiolytics. This study tested the hypothesis that anxiety behaviors during anticipation of negative images are sensitive to anxiolytic treatment.

METHOD

This study examined the effects of alprazolam and pregabalin treatment on potentiated startle during affective image anticipation.

RESULTS

There was an effect of anticipation type (negative versus neutral versus positive) on startle reactivity and subjective ratings, suggesting that the task was effective in assaying negative anticipatory arousal. Both treatments significantly reduced overall startle magnitude. However, neither treatment specifically affected potentiated startle during aversive anticipation.

CONCLUSION

These data suggest that potentiated startle in response to anticipation of aversive images is not sensitive to anxiolytic treatments in a healthy population, limiting its use as a predictive model of anxiolytic activity. This article is a US Government work and is in the public domain in the USA.