The Neurofunctional Basis of Affective Startle Modulation in Humans: Evidence From Combined Facial Electromyography and Functional Magnetic Resonance Imaging

Elemental and configural representation of a conditioned context

A context can be conceptualized as a stable arrangement of elements or as the sum of single elements. Both configural and elemental representations play a role in associative processes. This study aimed to explore the respective contributions of these two representations of a context in the acquisition of conditioned anxiety in humans. Virtual reality (VR) can be an ecologically valid tool to investigate context-related mechanisms, yet the influence of the sense of presence within the virtual environment remains unclear. Forty-eight healthy individuals participated in a VR-based context conditioning wherein electric shocks (unconditioned stimulus, US) were unpredictably delivered in one virtual office (CTX+), but not in the other (CTX-). During the test phase, nine elements from each context were presented singularly. We found a cluster of participants, who exhibited heightened anticipation of the US for anxiety-related elements as compared to the other group. In contrast to their clear elemental representation, these individuals showed diminished discriminative responses between the two context's configurations. Discriminative responses to the contexts were boosted in those individuals, who had a weaker elemental representation. Importantly, the individual sense of presence significantly influenced the conditioned responses. These findings align with the dual-representation view of context and provide insights into the role of presence in eliciting (conditioned) anxiety responses.

Neuropsychobiology of fear-induced bradycardia in humans: progress and pitfalls

In the last century, the paradigm of fear conditioning has greatly evolved in a variety of scientific fields. The techniques, protocols, and analysis methods now most used have undergone a progressive development, theoretical and technological, improving the quality of scientific productions. Fear-induced bradycardia is among these techniques and represents the temporary deceleration of heart beats in response to negative outcomes. However, it has often been used as a secondary measure to assess defensive responding to threat, along other more popular techniques. In this review, we aim at paving the road for its employment as an additional tool in fear conditioning experiments in humans. After an overview of the studies carried out throughout the last century, we describe more recent evidence up to the most contemporary research insights. Lastly, we provide some guidelines concerning the best practices to adopt in human fear conditioning studies which aim to investigate fear-induced bradycardia.

Unconditioned response to a naturally aversive stimulus is associated with sensitized defensive responding and self-reported fearful traits in a PTSD sample

Unconditioned responding (UCR) to a naturally aversive stimulus is associated with defensive responding to a conditioned threat cue (CS+) and a conditioned safety cue (CS-) in trauma-exposed individuals during fear acquisition. However, the relationships of UCR with defensive responses during extinction training, posttraumatic stress disorder (PTSD) symptom severity, and fearful traits in trauma-exposed individuals are not known. In a sample of 100 trauma-exposed adults with a continuum of PTSD severity, we recorded startle responses and skin conductance responses (SCR) during fear acquisition and extinction training using a 140 psi, 250-ms air blast to the larynx as the unconditioned stimulus. We explored dimensional associations of two different measures of UCR (unconditioned startle and unconditioned SCR) with conditioned defensive responding to CS+ and CS-, conditioned fear (CS+ minus CS-), PTSD symptom severity, and a measure of fearful traits (composite of fear survey schedule, anxiety sensitivity index, and Connor-Davidson resilience scale). Unconditioned startle was positively associated with startle potentiation to the threat cue and the safety cue across both learning phases (CS+ Acquisition, CS- Acquisition, CS+ Extinction Training, CS- Extinction Training) and with fearful traits. Unconditioned SCR was positively associated with SCR to the CS+ and CS- and SCR difference score during Acquisition. Neither type of UCR was associated with PTSD symptom severity. Our findings suggest that UCR, particularly unconditioned startle to a naturally aversive stimulus, may inform research on biomarkers and treatment targets for symptoms of pervasive and persistent fear in trauma-exposed individuals.

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.

The photic blink reflex as an index of photophobia

Two recent studies of eye closure triggered by intense luminance increase suggest that this behavior reflects the melanopsin-based retinal activity known to underlie photophobia, the pathological aversion to light (Kardon, 2012; Kaiser et al., 2021). Early studies of the photic blink reflex (PBR) are reviewed to help guide future research on this possible objective index of photophobia. Electromyographic recordings of the lid-closure muscle, orbicularis oculi, reveal distinct bursts with typical onset latencies of 50 and 80 ms, R50 and R80, respectively. The latter component appears to be especially sensitive to visual signals from intrinsically photosensitive retinal ganglion cells (ipRGCs) and to prior trigeminal nociceptive stimuli. The authors argue that the R80's function, in addition to protecting the eyeballs from physical contact, is to shape the upper and lower eyelids into a narrow slit to restrict incoming light. This serves to prevent retinal bleaching or injury, while allowing continued visual function.

The unique face of anxious depression: Increased sustained threat circuitry response during fear acquisition

Background

Sensitivity to threat with dysregulation of fear learning is thought to contribute to the development of psychiatric disorders, including anxiety disorders (AD) and major depressive disorder (MDD). However, fewer studies have examined fear learning in MDD than in AD. Nearly half of individuals with MDD have an AD and the comorbid diagnosis has worse outcomes. The current study used propensity matching to examine the hypothesis that AD+MDD shows greater neural correlates of fear learning than MDD, suggesting that the co-occurrence of AD+MDD is exemplified by exaggerated defense related processes.

Methods

195 individuals with MDD (N = 65) or AD+MDD (N=130) were recruited from the community and completed multi-level assessments, including a Pavlovian fear learning task during functional imaging.

Results

MDD and AD+MDD showed significantly different patterns of activation for [CSplus-CSminus] in the medial amygdala (ηp2=0.009), anterior insula (ηp2=0.01), dorsolateral prefrontal cortex (ηp2=0.002), dorsal anterior cingulate cortex (ηp2=0.01), mid-cingulate cortex (ηp2=0.01) and posterior cingulate cortex (ηp2=0.02). These differences were driven by greater activation to the CS+ in late conditioning phases in ADD+MDD relative to MDD.

Conclusions

AD+MDD showed a pattern of increased sustained activation in regions identified with fear learning. Effects were consistently driven by the threat condition, further suggesting fear signaling as the emergent target process. Differences emerged in regions associated with salience processing, attentional orienting/conflict, and self-relevant processing.These findings help to elucidate the fear signaling mechanisms involved in the pathophysiology of comorbid anxiety and depression, thereby highlighting promising treatment targets for this prevalent treatment group.

The effect of ketamine on affective modulation of the startle reflex and its resting-state brain correlates

Ketamine is a rapid-acting antidepressant that also influences neural reactivity to affective stimuli. However, the effect of ketamine on behavioral affective reactivity is yet to be elucidated. The affect-modulated startle reflex paradigm (AMSR) allows examining the valence-specific aspects of behavioral affective reactivity. We hypothesized that ketamine alters the modulation of the startle reflex during processing of unpleasant and pleasant stimuli and weakens the resting-state functional connectivity (rsFC) within the modulatory pathway, namely between the centromedial nucleus of the amygdala and nucleus reticularis pontis caudalis. In a randomized, double-blind, placebo-controlled, cross-over study, thirty-two healthy male participants underwent ultra-high field resting-state functional magnetic resonance imaging at 7 T before and 24 h after placebo and S-ketamine infusions. Participants completed the AMSR task at baseline and one day after each infusion. In contrast to our hypothesis, ketamine infusion did not impact startle potentiation during processing of unpleasant stimuli but resulted in diminished startle attenuation during processing of pleasant stimuli. This diminishment significantly correlated with end-of-infusion plasma levels of ketamine and norketamine. Furthermore, ketamine induced a decrease in rsFC within the modulatory startle reflex pathway. The results of this first study on the effect of ketamine on the AMSR suggest that ketamine might attenuate the motivational significance of pleasant stimuli in healthy participants one day after infusion.

Comprehensive behavioral analyses of mice with a glycine receptor alpha 4 deficiency

Glycine receptors (GlyRs) are ligand-gated chloride channels comprising alpha (α1-4) and β subunits. The GlyR subunits play major roles in the mammalian central nervous system, ranging from regulating simple sensory information to modulating higher-order brain function. Unlike the other GlyR subunits, GlyR α4 receives relatively little attention because the human ortholog lacks a transmembrane domain and is thus considered a pseudogene. A recent genetic study reported that the GLRA4 pseudogene locus on the X chromosome is potentially involved in cognitive impairment, motor delay and craniofacial anomalies in humans. The physiologic roles of GlyR α4 in mammal behavior and its involvement in disease, however, are not known. Here we examined the temporal and spatial expression profile of GlyR α4 in the mouse brain and subjected Glra4 mutant mice to a comprehensive behavioral analysis to elucidate the role of GlyR α4 in behavior. The GlyR α4 subunit was mainly enriched in the hindbrain and midbrain, and had relatively lower expression in the thalamus, cerebellum, hypothalamus, and olfactory bulb. In addition, expression of the GlyR α4 subunit gradually increased during brain development. Glra4 mutant mice exhibited a decreased amplitude and delayed onset of the startle response compared with wild-type littermates, and increased social interaction in the home cage during the dark period. Glra4 mutants also had a low percentage of entries into open arms in the elevated plus-maze test. Although mice with GlyR α4 deficiency did not show motor and learning abnormalities reported to be associated in human genomics studies, they exhibited behavioral changes in startle response and social and anxiety-like behavior. Our data clarify the spatiotemporal expression pattern of the GlyR α4 subunit and suggest that glycinergic signaling modulates social, startle, and anxiety-like behaviors in mice.

Don't worry, it won't be fine. Contributions of worry and anxious arousal to startle responses and event-related potentials in threat anticipation

A widely shared framework suggests that anxiety maps onto two dimensions: anxious apprehension and anxious arousal. Previous research linked individual differences in these dimensions to differential neural response patterns in neuropsychological, imaging, and physiological studies. Differential effects of the anxiety dimensions might contribute to inconsistencies in prior studies that examined neural processes underlying anxiety, such as hypersensitivity to unpredictable threat. We investigated the association between trait worry (as a key component of anxious apprehension), anxious arousal, and the neural processing of anticipated threat. From a large online community sample (N = 1,603), we invited 136 participants with converging and diverging worry and anxious arousal profiles into the laboratory. Participants underwent the NPU-threat test with alternating phases of unpredictable threat, predictable threat, and safety, while physiological responses (startle reflex and startle probe locked event-related potential components N1 and P3) were recorded. Worry was associated with increased startle responses to unpredictable threat and increased attentional allocation (P3) to startle probes in predictable threat anticipation. Anxious arousal was associated with increased startle and N1 in unpredictable threat anticipation. These results suggest that trait variations in the anxiety dimensions shape the dynamics of neural processing of threat. Specifically, trait worry seems to simultaneously increase automatic defensive preparation during unpredictable threat and increase attentional responding to threat-irrelevant stimuli during predictable threat anticipation. The current study highlights the utility of anxiety dimensions to understand how physiological responses during threat anticipation are altered in anxiety and supports that worry is associated with hypersensitivity to unpredictable, aversive contexts.

Watching with Argus eyes: Characterization of emotional and physiological responding in adults exposed to childhood maltreatment and/or recent adversity

Exposure to adverse experiences is a well-established major risk factor for affective psychopathology. The vulnerability of deleterious sequelae is assumed in maladaptive processes of the defensive system, particularly in emotional processing. More specifically, childhood maltreatment has been suggested to be associated with the recruitment of specific and distinct defensive response profiles. To date, it remains unclear whether these are specific or generalizable to recent adversity in adulthood. This pre-registered study aimed to investigate the impact of exposure to childhood and recent adversity on emotional processing in 685 healthy adults with the "Affective Startle Modulation" Paradigm (ASM). First, we replicated higher trait anxiety and depression levels in individuals exposed to both types of adversity. Second, we observed increased general skin conductance reactivity in individuals exposed to recent adversity. Third, individuals exposed to childhood maltreatment showed reduced, while individuals exposed to recent adversity showed increased discrimination between pictures of negative and neutral valence, compared with non-exposed individuals in SCR. No association between exposure to adversity and fear potentiated startle was observed. Furthermore, explorative analyses revealed moderate dimensional and categorical agreement between two childhood maltreatment questionnaires and provide insight into potential adversity-type specific effects. Our results support experience-dependent plasticity in sympathetic nervous system reactivity and suggest distinct response profiles in affective modulation in individuals exposed to early versus recent adversity. We emphasize the need to further explore distinct adversity profiles to further our understanding on specific psychophysiological profiles and their potential implication for prevention and intervention.

Facilitated extinction but impaired extinction recall by eye movement manipulation in humans - Indications for action mechanisms and the applicability of eye movement desensitization

Eye movement desensitization and reprocessing (EMDR) therapy utilizes the manipulation of eye movements to reduce affective distress during fear-exposure. Animal research recently suggested a potential neural mechanism underlying these effects, by which increased activity of the superior colliculus (SC), mediating visual attention, increases the inhibition of the basolateral amygdala (BLA), mediating defensive plasticity. We tested such mechanism in forty healthy humans using a multiple-day single-cue fear conditioning and extinction paradigm. The activity of the SC during extinction was experimentally manipulated by eye movements, as half of the participants executed saccadic eye movements (n = 20; major SC involvement), while the other half executed smooth eye pursuits (n = 20; minor SC involvement). Amygdala-mediated fear-potentiated startle responses and fear bradycardia, as well as threat expectancy was analyzed. Saccadic eye movements facilitated the extinction of fear bradycardia and fear-potentiated startle responses. Higher saccadic accuracy and range correlated with reduced fear-potentiated startle. However, during extinction recall, fear-potentiated startle and fear bradycardia resurged and partly reached levels obtained after fear acquisition. Threat expectancy was not affected by different eye movements and was not elevated during extinction recall. Within limitations, results support an inhibitory SC-BLA pathway in humans by which eye movements may reduce low-level defensive responding, but not threat expectancy. Yet, manipulating eye movements during extinction learning seems to impair extinction recall for behavioral and physiological defensive response indices. Thus, increasing SC activity might enhance initial efficacy of exposure treatment, but additional strategies seem necessary for sustained fear attenuation.

Fear-potentiated startle reveals diminished threat extinction in pathological anxiety

BACKGROUND

Major theories propose that perturbed threat learning is central to pathological anxiety, but empirical support is inconsistent. Failures to detect associations with anxiety may reflect limitations in quantifying conditioned responses to anticipated threat, and hinder translation of theory into empirical work. In prior work, we could not detect threat-specific anxiety effects on states of conditioned threat using psychophysiology in a large sample of patients and healthy comparisons. Here, we examine the utility of an alternative fear potentiated startle (FPS) scoring in revealing associations between anxiety and threat conditioning and extinction in this dataset. Secondary analyses further explored associations among conditioned threat responses, subcortical morphometry, and treatment outcomes.

METHODS

Youths and adults with anxiety disorders and healthy comparisons (n = 306; 178 female participants; 8-50 years) previously completed a well-validated differential threat learning paradigm. FPS and skin conductance response (SCR) quantified psychophysiological responses during threat conditioning and extinction. In this report, we examined normalizing raw FPS scores to intertrial intervals (ITI) to address challenges in more common approaches to FPS scoring which could mask group effects. Secondary analyses examined associations between FPS and subcortical morphometry and with response to exposure-based cognitive behavioral therapy in a subsample of patients.

RESULTS

Patients and comparisons showed comparable differential threat conditioning using FPS and SCR. While SCR suggested comparable extinction between groups, FPS revealed stronger retention of threat contingency during extinction in individuals with anxiety disorders. Extinction indexed with FPS was not associated with age, morphometry, or anxiety treatment outcome.

CONCLUSION

ITI-normalized FPS may have utility in detecting difficulties in extinguishing conditioned threat responses in anxiety. These findings provide support for extinction theories of anxiety and encourage continued research on aberrant extinction in pathological anxiety.

Getting Better with Age? A Review of Psychophysiological Studies of Fear Extinction Learning Across Development

A critical developmental task is learning what constitutes reliable threat and safety signals in the environment. In humans, atypical fear learning processes are implicated in many mental health conditions, particularly fear and anxiety disorders, pointing to the potential for laboratory measures of fear learning to facilitate early identification of at-risk individuals. This chapter reviews studies of fear learning and extinction learning that incorporate peripheral measures of psychophysiological response and include a developmental sample. Broadly, these studies indicate substantial consistency in differential learning and extinction across development, as assessed with multiple paradigms, across physiological indices. Importantly, though, response coherence across measures (e.g., physiological, neural, and behavioral) was inconsistent across studies. There was also less consistency in results from studies that probed associations between anxiety and fear learning processes. These mixed findings highlight the need for additional examination of when and why there is variability, both across development and in relation to individual differences factors, including mental health, childhood adversity, and sex. In addition, there remains a need for studies that test for developmental change in extinction recall learning and whether stimulus type impacts learning across development. Longitudinal studies designed to address these questions could provide novel insight into the developmental trajectory of fear learning and extinction.

Deriving psychiatric symptom-based biomarkers from multivariate relationships between psychophysiological and biochemical measures

Identification of biomarkers for psychiatric disorders remains very challenging due to substantial symptom heterogeneity and diagnostic comorbidity, limiting the ability to map symptoms to underlying neurobiology. Dimensional symptom clusters, such as anhedonia, hyperarousal, etc., are complex and arise due to interactions of a multitude of complex biological relationships. The primary aim of the current investigation was to use multi-set canonical correlation analysis (mCCA) to derive biomarkers (biochemical, physiological) linked to dimensional symptoms across the anxiety and depressive spectrum. Active-duty service members (N = 2,592) completed standardized depression, anxiety and posttraumatic stress questionnaires and several psychophysiological and biochemical assays. Using this approach, we identified two phenotype associations between distinct physiological and biological phenotypes. One was characterized by symptoms of dysphoric arousal (anhedonia, anxiety, hypervigilance) which was associated with low blood pressure and startle reactivity. This finding is in line with previous studies suggesting blunted physiological reactivity is associated with subpopulations endorsing anxiety with comorbid depressive features. A second phenotype of anxious fatigue (high anxiety and reexperiencing/avoidance symptoms coupled with fatigue) was associated with elevated blood levels of norepinephrine and the inflammatory marker C-reactive protein in conjunction with high blood pressure. This second phenotype may describe populations in which inflammation and high sympathetic outflow might contribute to anxious fatigue. Overall, these findings support the growing consensus that distinct neuropsychiatric symptom patterns are associated with differential physiological and blood-based biological profiles and highlight the potential of mCCA to reveal important psychiatric symptom biomarkers from several psychophysiological and biochemical measures.

Stimulation of the ventromedial prefrontal cortex blocks the return of subcortically mediated fear responses

The ventromedial prefrontal cortex (vmPFC) mediates the inhibition of defensive responses upon encounters of cues, that had lost their attribute as a threat signal via previous extinction learning. Here, we investigated whether such fear extinction recall can be facilitated by anodal transcranial direct current stimulation (tDCS). Extinction recall was tested twenty-four hours after previously acquired fear was extinguished. Either anodal tDCS or sham stimulation targeting the vmPFC was applied during this test. After stimulation ceased, we examined return of fear after subjects had been re-exposed to aversive events. Fear was assessed by reports of threat expectancy and modulations of autonomic (skin conductance, heart rate) and protective reflex (startle potentiation) measures, the latter of which are mediated by subcortical defense circuits. While tDCS did not affect initial extinction recall, it abolished the return of startle potentiation and autonomic components of the fear response. Results suggest hierarchical multi-level vmPFC functions in human fear inhibition and indicate, that its stimulation might immunize against relapses into pathological subcortically mediated defensive activation.

Coping in the Clinic: Effects of Clinically Elevated Anxiety on Dynamic Neurophysiological Mechanisms of Escape/Avoidance Preparation

BACKGROUND

Treatments for anxiety and related disorders target exaggerated escape/avoidance as a core feature, but current methods fail to improve escape/avoidance habits for many treatment-seeking individuals. To support developing tools that increase treatment efficacy by targeting mechanisms more directly, the current work examined potential distinctions in the neurophysiologies of escape and avoidance and tested how clinical anxiety affects these neurophysiologies.

METHODS

Twenty-five treatment-seeking individuals with varied principal diagnoses (e.g., generalized anxiety disorder, posttraumatic stress disorder) and 20 non-treatment-seeking control subjects participated. In the study task, approximately 5.25-second cues predicted aversive images that could be avoided (blocked by a button press before image onset), escaped (ended by a button press after image onset), or not controlled. To examine neural processing and defensive response modulation, anticipatory event-related potentials were derived, and startle reflexes were probed throughout each cue.

RESULTS

Multidimensional profiles were observed such that 1) anticipatory event-related potential enhancement was only reliable during avoidance preparation, and event-related potentials potentially reflected perceived/instrumental control; and 2) startle reflexes were inhibited during avoidance preparation, relatively enhanced during escape preparation, and further enhanced during uncontrollable anticipation, thus potentially reflecting fear-related activation. Treatment-seeking status, then, did not affect cortical processing, but it did moderate context-dependent fear (if individuals with severe depression were excluded) such that treatment-seeking individuals without depression showed exaggerated startle during escape, but not avoidance, preparation.

CONCLUSIONS

Data suggest a specific effect of anxiety on fear system activation during preparation to escape aversion. This effect warrants further investigation as a precision target for interventions that directly modulate the specific underlying neural circuitry.

A rare scare: The role of intolerance of uncertainty in startle responses and event-related potentials in anticipation of unpredictable threat

Intolerance of uncertainty (IU) represents a transdiagnostic risk factor for internalizing psychopathology. However, little is known regarding its psychophysiological correlates. IU is thought to render individuals hypersensitive to threatening events, even if the occurrence probability is low. To test this, we recruited 90 students who completed two NPU-threat tests separating temporal unpredictability from probabilistic unpredictability (i.e., probability of occurrence): First, a NPU version in which the timing of threat (i.e., shock) was either predictable or unpredictable but the shock probability was 100 % in each trial. Second, a probabilistic NPU version in which the timing of the shock was also either predictable or unpredictable, but the shock probability was 33 % in each trial. Startle reflex, event-related potentials N1 and P3 locked to auditory startle probes, and anxiety ratings were analyzed. As expected, temporally unpredictable threat modulated startle, N1, and anxiety ratings. IU predicted increased startle to lower shock probability, regardless of the temporal predictability. No evidence emerged for IU affecting N1 or P3. However, IU predicted anxiety ratings to threat conditions regardless of temporal or probabilistic predictability. Individual differences in IU shape startle responses to eventual threat: IU increases automatic defensive responding to unpredictable and potentially threatening situations if the threat probability is low. Individuals with higher IU may tend to "err on the side of caution" with a mismatch between physiological preparation and threat probability, such that the effects of IU are particularly observable in low threat probability conditions.

Startle Latency as a Potential Marker for Amygdala-Mediated Hyperarousal

BACKGROUND

Fear-related disorders are characterized by hyperexcitability in reflexive circuits and maladaptive associative learning mechanisms. The startle reflex is suited to investigate both processes, either by probing it under baseline conditions or by deriving it in fear conditioning studies. In anxiety research, the amplitude of the fear-potentiated startle has been shown to be influenced by amygdalar circuits and has typically been the readout of interest. In schizophrenia research, prolonged startle peak latency under neutral conditions is an established readout, thought to reflect impaired processing speed. We therefore explored whether startle latency is an informative readout for human anxiety research.

METHODS

We investigated potential similarities and differences of startle peak latency and amplitude derived from a classical fear conditioning task in a sample of 206 participants with varying severity levels of anxiety disorders and healthy control subjects. We first reduced startle response to stable components and regressed individual amygdala gray matter volumes onto the resulting startle measures. We then probed time, stimulus, and group effects of startle latency.

RESULTS

We showed that startle latency and startle amplitude were 2 largely uncorrelated measures; startle latency, but not amplitude, showed a sex-specific association with gray matter volume of the amygdala; startle latencies showed a fear-dependent task modulation; and patients with fear-related disorders displayed shorter startle latencies throughout the fear learning task.

CONCLUSIONS

These data provide support for the notion that probing startle latencies under threat may engage amygdala-modulated threat processing, making them a complementary marker for human anxiety research.

The human insula processes both modality-independent and pain-selective learning signals

Prediction errors (PEs) are generated when there are differences between an expected and an actual event or sensory input. The insula is a key brain region involved in pain processing, and studies have shown that the insula encodes the magnitude of an unexpected outcome (unsigned PEs). In addition to signaling this general magnitude information, PEs can give specific information on the direction of this deviation-i.e., whether an event is better or worse than expected. It is unclear whether the unsigned PE responses in the insula are selective for pain or reflective of a more general processing of aversive events irrespective of modality. It is also unknown whether the insula can process signed PEs at all. Understanding these specific mechanisms has implications for understanding how pain is processed in the brain in both health and in chronic pain conditions. In this study, 47 participants learned associations between 2 conditioned stimuli (CS) with 4 unconditioned stimuli (US; painful heat or loud sound, of one low and one high intensity each) while undergoing functional magnetic resonance imaging (fMRI) and skin conductance response (SCR) measurements. We demonstrate that activation in the anterior insula correlated with unsigned intensity PEs, irrespective of modality, indicating an unspecific aversive surprise signal. Conversely, signed intensity PE signals were modality specific, with signed PEs following pain but not sound located in the dorsal posterior insula, an area implicated in pain intensity processing. Previous studies have identified abnormal insula function and abnormal learning as potential causes of pain chronification. Our findings link these results and suggest that a misrepresentation of learning relevant PEs in the insular cortex may serve as an underlying factor in chronic pain.

Pleasant touch perception in borderline personality disorder and its relationship with disturbed body representation

BACKGROUND

Borderline personality disorder (BPD) is characterized by altered perception of affective stimuli, including abnormal evaluation of nociceptive input. However, whether or not perceptual alterations are present for its positive counterpart, i.e. pleasant touch (PT), has not yet been examined.

METHODS

In the present study, we applied standardized PT stimuli to the hands of 25 patients with BPD and 25 healthy controls (HC) and compared their perception. We used the affect-modulated acoustic startle response as a physiological correlate of affective processing. We further explored the effect of PT stimulation on dissociative experiences in BPD.

RESULTS

Compared to HC, BPD perceived PT as less pleasant and less intense. The effect on perceived valence of touch was large even after controlling for the effect of reduced perceived intensity of touch (ƞ² = .29). We further found qualitative alterations in touch perception in BPD, who rated the touch as significantly rougher and firmer compared to HC. There was a positive correlation between perceived valence of touch and changes in dissociative experiences in terms of body ownership of the stimulated body part from pre to post stimulation, suggesting that a more negative evaluation of touch is associated with an increase in body-related dissociative experiences, while a positive perception of touch might be related to a reduction of these dissociative experiences.

CONCLUSIONS

Our results confirm BPD-associated disturbances in the processing of affective somatosensory stimuli and indicate that not only pain perception but also pleasant touch perception is diminished in BPD. We discuss the role of altered touch perception for BPD psychopathology and its potential role for new treatment approaches.

An Investigation of Awareness and Metacognition in Neurofeedback with the Amygdala Electrical Fingerprint

Awareness theory posits that individuals connected to a brain-computer interface can learn to estimate and discriminate their brain states. We used the amygdala Electrical Fingerprint (amyg-EFP) - a functional Magnetic Resonance Imaging-inspired Electroencephalogram surrogate of deep brain activation - to investigate whether participants could accurately estimate their own brain activation. Ten participants completed up to 20 neurofeedback runs and estimated their amygdala-EFP activation (depicted as a thermometer) and confidence in this rating during each trial. We analysed data using multilevel models, predicting the real thermometer position with participant rated position and adjusted for activation during the previous trial. Hypotheses on learning regulation and improvement of estimation were not confirmed. However, participant ratings were significantly associated with the amyg-EFP signal. Higher rating accuracy also predicted higher subjective confidence in the rating. This proof-of-concept study introduces an approach to study awareness with fMRI-informed neurofeedback and provides initial evidence for metacognition in neurofeedback.

Startling Acoustic Stimulation Has Task-Specific Effects on Intracortical Facilitation and Inhibition at Rest and During Visually Guided Isometric Elbow Flexion in Healthy Individuals

Startling acoustic stimulation (SAS) causes a transient effect on the primary motor cortex (M1) nonreflexively. It reduces the cortical excitability at rest, but not during voluntary contraction. However, the effect of SAS on intracortical activity is not clear. The purpose of this study was to investigate the SAS effect on short-interval intracortical inhibition and intracortical facilitation using transcranial magnetic stimulation (TMS). Eleven healthy individuals performed isometric elbow flexion at 10% of maximum voluntary contraction on the dominant side with a real-time visual target (i.e., M1 preactivation) or at rest. TMS was delivered to the M1 ipsilateral to elbow flexion without or with SAS delivered 90 ms prior to TMS. There were three TMS delivery conditions: (a) single pulse, (b) short-interval intracortical inhibition, and (c) intracortical facilitation. TMS-induced motor-evoked potential (MEP) was compared between predetermined TMS and SAS conditions at rest and during ipsilateral voluntary contraction. We confirmed that SAS decreased the MEP amplitude at rest, but not during M1 preactivation. SAS caused task-specific effects on intracortical excitability. Specifically, SAS increased intracortical facilitation at rest and during voluntary contraction. However, SAS decreased short-interval intracortical inhibition only during M1 preactivation. Collectively, our results suggest that SAS transiently influences the motor cortex excitability, possibly via its activation of higher centers, to achieve a visually guided goal-directed task.

Defensive Mobilization During Anticipation of Symptom Provocation: Association With Panic Pathology

BACKGROUND

Anxious apprehension about feared body symptoms is thought to play a crucial role in the development, chronicity, and treatment of panic disorder (PD). In this study, we therefore aimed to elucidate the role of defensive reactivity to anticipated unpleasant symptoms in PD that can contribute to a better understanding of pathomechanisms of PD as well as identification of potential targets in PD-focused interventions. By measuring amygdala-dependent potentiation of the startle reflex, we aimed to investigate whether 1) patients with PD exhibit a specifically increased defensive reactivity to anticipated unpleasant body symptoms and 2) whether clinical severity of panic symptomatology varies with magnitude of defensive activation.

METHODS

Defensive mobilization to anticipated threat was investigated in 73 patients with a primary diagnosis of PD with agoraphobia (PDA) and 52 healthy control subjects. Threat of symptom provocation was established by a standardized hyperventilation task and contrasted to threat of shock to the forearm of the participant.

RESULTS

Patients with PDA and healthy control subjects did not differ in their defensive responses during anticipation of shock. In contrast, patients with severe PDA as compared with healthy control subjects exhibited increased defensive response mobilization and reported more anxiety and panic symptoms during anticipation of feared body symptoms. Moreover, startle potentiation during anticipation of hyperventilation covaried with the severity of panic symptomatology.

CONCLUSIONS

The present findings suggest that increased defensive mobilization during anticipation of body symptoms is a neurobiological correlate of severe PDA that should be specifically targeted in PD interventions and might be used to monitor treatment success.

Dissociable impact of childhood trauma and deployment trauma on affective modulation of startle

Trauma disorders are often associated with alterations in aversive anticipation and disruptions in emotion/fear circuits. Heightened or blunted anticipatory responding to negative cues in adulthood may be due to differential trauma exposure during development, and previous trauma exposure in childhood may also modify effects of subsequent trauma in adulthood. The aim of the current investigation was to examine the contributions of childhood trauma on affective modulation of startle before and after trauma exposure in adulthood (a combat deployment). Adult male participants from the Marine Resilience Study with (n = 1145) and without (n = 1312) a history of reported childhood trauma completed an affective modulation of startle task to assess aversive anticipation. Affective startle response was operationalized by electromyography (EMG) recording of the orbicularis oculi muscle in response to acoustic stimuli when anticipating positive and negative affective images. Startle responses to affective images were also assessed. Testing occurred over three time-points; before going on a 7 month combat deployment and 3 and 6 months after returning from deployment. Startle response when anticipating negative images was greater compared to pleasant images across all three test periods. Across all 3 time points, childhood trauma was consistently associated with significantly blunted startle when anticipating negative images, suggesting reliable effects of childhood trauma on aversive anticipation. Conversely, deployment trauma was associated with increased startle reactivity post-deployment compared to pre-deployment, which was independent of childhood trauma and image valence. These results support the hypothesis that trauma exposure during development vs. adulthood may have dissociable effects on aversive anticipation and arousal mechanisms. Further study in women and across more refined age groups is needed to test generalizability and identify potential developmental windows for these differential effects.

Hold your breath: Voluntary breath-holding time predicts defensive activation to approaching internal threat

Bodily disturbances, like dyspnea, elicit responses to regain homeostasis and ensure survival. However, this life-saving function can become hyperreactive, which may lead to the emergence of psychopathology. This study investigated whether maximal voluntary breath-holding time (mvBHT), a biobehavioral marker that characterizes sensitivity to respiratory stimulation, predicts defensive mobilization to cues signaling the proximity of a mild electric shock vs. a respiratory threat (shortness of breath elicited by forced breath-holding) and the opportunity to avoid threat delivery in 60 healthy participants. While the startle reflex, a measure of defensive mobilization, generally increased with the proximity of an inevitable threat, shorter breath-holding time was specifically associated with greater startle potentiation when anticipating a respiratory threat but not an electric shock. In contrast, when both threats were avoidable, the startle reflex was comparably inhibited, irrespective of mvBHT. This study suggests that mvBHT specifically predicts hypersensitive responding to an anticipated inevitable respiratory threat.

Closing the species gap: Translational approaches to studying sensory processing differences relevant for autism spectrum disorder

The study of sensory phenotypes has great potential for increasing research translation between species, a necessity to decipher the neural mechanisms that contribute to higher-order differences in neurological conditions such as autism spectrum disorder (ASD). Over the past decade, despite separate advances in our understanding of the structural and functional differences within the brain of autistic and non-autistic individuals and in rodent models for ASD, researchers have had difficulty translating the findings in murine species to humans, mostly due to incompatibility in experimental methodologies used to screen for ASD phenotypes. Focusing on sensory phenotypes offers an avenue to close the species gap because sensory pathways are highly conserved across species and are affected by the same risk-factors as the higher-order brain areas mostly responsible for the diagnostic criteria for ASD. By first reviewing how sensory processing has been studied to date, we direct our focus to electrophysiological and behavioral techniques that can be used to study sensory phenotypes consistently across species. Using auditory sensory phenotypes as a template, we seek to improve the accessibility of translational methods by providing a framework for collecting cohesive data in both rodents and humans. Specifically, evoked-potentials, acoustic startle paradigms, and psychophysical detection/discrimination paradigms can be created and implemented in a coordinated and systematic fashion across species. Through careful protocol design and collaboration, sensory processing phenotypes can be harnessed to bridge the gap that exists between preclinical animal studies and human testing, so that mutually held questions in autism research can be answered. LAY SUMMARY: It has always been difficult to relate results from animal research to humans. We try to close this gap by studying changes in sensory processing using careful protocol design and collaboration between clinicians and researchers. Sensory pathways are comparable between animals and humans, and are affected in the same way as the rest of the brain in ASD. Using changes in hearing as a template, we point the field in an innovative direction by providing a framework for collecting cohesive data in rodents and humans.

Covariate effects of resting heart rate variability on affective ratings and startle reflex during cognitive reappraisal of negative emotions

Heart Rate Variability (HRV) has been widely studied in laboratory settings due to its clinical implications, primarily as a potential biomarker of emotion regulation (ER). Studies have reported that individuals with higher resting HRV show more distinct startle reflexes to negative stimuli as compared to those with lower HRV. These responses have been associated with better defense system function when managing the context demands. There is, however, a lack of empirical evidence on the association between resting HRV and eyeblinks during laboratory tasks using instructed ER. This study explored the influence of tonic HRV on voluntary cognitive reappraisal through subjective and startle responses measured during an independent ER task. In total, 122 healthy participants completed a task consisting of attempts to upregulate, downregulate, or react naturally to emotions prompted by unpleasant pictures. Tonic HRV was measured for 5 minutes before the experiment began. Current results did not support the idea that self-reported and eyeblink responses were influenced by resting HRV. These findings suggest that, irrespective of resting HRV, individuals may benefit from strategies such as reappraisal that are useful for managing negative emotions. Experimental studies should further explore the role of individual differences when using ER strategies during laboratory tasks.

Contactless differentiation of pleasant and unpleasant valence: Assessment of the acoustic startle eyeblink response with infrared reflectance oculography

The ability to distinguish between discrete emotions by monitoring autonomic or facial features has been an elusive "holy grail" for fields such as psychophysiology, affective computing, and human-computer interface design. However, cross-validated models are lacking, and contemporary theory suggests that emotions may lack distinct physiological or facial "signatures." Therefore, in this study, we propose a reorientation toward distinguishing between pleasant and unpleasant affective valence. We focus on the acoustic eyeblink response, which exhibits affective modulation but remains underutilized. The movement of the eyelid was monitored in a contactless manner via infrared reflectance oculography at 1 kHz while 36 participants viewed normatively pleasant, neutral, and unpleasant images, and 50-ms bursts of white noise were presented binaurally via headphones. Startle responses while viewing pleasant images exhibited significantly smaller amplitudes than those while viewing unpleasant images, with a large effect size (d = 1.56). The affective modulation of the eyeblink startle response is a robust phenomenon that can be assessed in a contactless manner. As research continues on whether systems based on psychophysiological or facial features can distinguish between discrete emotions, the eyeblink startle response offers a relatively simple way to distinguish between pleasant and unpleasant affective valence.

Decreased defensive reactivity to interoceptive threat after successful exposure-based psychotherapy in patients with panic disorder

Panic disorder (PD) is characterized by a dysfunctional defensive responding to panic-related body symptoms that is assumed to contribute to the persistence of panic symptomatology. The present study aimed at examining whether this dysfunctional defensive reactivity to panic-related body symptoms would no longer be present following successful cognitive behavior therapy (CBT) but would persist when patients show insufficient symptom improvement. Therefore, in the present study, effects of CBT on reported symptoms and defensive response mobilization during interoceptive challenge were investigated using hyperventilation as a respiratory symptom provocation procedure. Changes in defensive mobilization to body symptoms in the course of CBT were investigated in patients with a primary diagnosis of PD with or without agoraphobia by applying a highly standardized hyperventilation task prior to and after a manual-based CBT (n = 38) or a waiting period (wait-list controls: n = 20). Defensive activation was indexed by the potentiation of the amygdala-dependent startle eyeblink response. All patients showed a pronounced defensive response mobilization to body symptoms at baseline. After treatment, no startle reflex potentiation was found in those patients who showed a clinically significant improvement. However, wait-list controls and treatment non-responders continued to show increased defensive responses to actually innocuous body symptoms after the treatment/waiting period. The present results indicate that the elimination of defensive reactivity to actually innocuous body symptoms might be a neurobiological correlate and indicator of successful CBT in patients with PD, which may help to monitor and optimize CBT outcomes.

Neural Abnormalities in Fear Generalization in Schizophrenia and Associations With Negative Symptoms

BACKGROUND

Associative learning and memory processes, including the generalization of previously learned associations, may be altered in schizophrenia. Deficits in schizophrenia in stimulus generalization, one of the simplest forms of memory, could interfere with the ability to efficiently categorize related, similar information, potentially leading to impairments in daily functioning.

METHODS

To measure generalization in schizophrenia, 37 individuals with a nonaffective psychotic disorder and 32 demographically matched healthy control subjects underwent a Pavlovian fear conditioning and generalization procedure, which accounted for variation in perceptual ability across participants, while undergoing functional magnetic resonance imaging. Skin conductance and neural responses to conditioned (CS+), neutral (CS-), and generalization stimuli were measured. Explicit memory ratings reflecting successful generalization were also collected after the scanning, as well as measures of symptom severity.

RESULTS

Compared with healthy control subjects, individuals with nonaffective psychotic disorders showed significant deficits in fear generalization across multiple measurements, with impairments in memory ratings and reductions in activation and deactivation of the salience and default networks, respectively, during fear generalization. Moreover, in the psychotic disorder group, greater behavioral and neural abnormalities in generalization were associated with higher levels of negative symptoms.

CONCLUSIONS

Fear generalization is impaired in psychotic illness. Given that successful generalization relies on a dynamic balance between excitatory and inhibitory neurotransmission, these results reveal a potentially quantifiable mechanism linked to negative symptoms that can be investigated further in future human and experimental animal studies.

Observational learning of fear in real time procedure

Learning to avoid threats often occurs by observing others. Most previous research on observational fear learning (OFL) in humans has used pre-recorded standardized video of an actor and thus lacked ecological validity. Here, we aimed to enhance ecological validity of the OFL by engaging participants in a real-time observational procedure (35 pairs of healthy male friends, age 18-27). One of the participants watched the other undergo a differential fear conditioning task, in which a conditioned stimulus (CS+) was paired with an aversive electric shock and another stimulus (CS-) was always safe. Subsequently, the CS+ and CS- were presented to the observer to test the OFL. While the friend's reactions to the shock elicited strong skin conductance responses (SCR) in all observers, subsequent differential SCRs (CS+ > CS-) were found only when declarative knowledge of the CS+/US contingency (rated by the participants) was acquired. Contingency-aware observers also showed elevated fear potentiated startle responses during both CS+ and CS- compared to baseline. We conclude that our real-time procedure can be effectively used to study OFL. The procedure allowed for dissecting two components of the OFL: an automatic emotional reaction to the response of the demonstrator and learning about stimulus contingency.

Aversive perception in a threat context: Separate and independent neural activation

Unpleasant, compared to neutral, scenes reliably prompt enhanced functional brain activity in the amygdala and inferotemporal cortex. Considering data from psychophysiological studies in which defensive reactivity is further enhanced when viewing unpleasant scenes under threat of shock (compared to safety), the current study investigates functional activation in the amygdala-inferotemporal circuit when unpleasant (or neutral) scenes are viewed under threat of shock or safety. In this paradigm, a cue signaling threat or safety was presented in conjunction with either an unpleasant or neutral picture. Replicating previous studies, unpleasant, compared to neutral, scenes reliably enhanced activation in the amygdala and inferotemporal cortex. Functional activity in these regions, however, did not differ whether scenes were presented in a context threatening shock exposure, compared to safety, which instead activated regions of the anterior insula and cingulate cortex. Taken together, the data support a view in which neural regions activated in different defensive situations act independently.

Psychophysiological Effects of Downregulating Negative Emotions: Insights From a Meta-Analysis of Healthy Adults

Assessing psychophysiological responses of emotion regulation is a cost-efficient way to quantify emotion regulation and to complement subjective report that may be biased. Previous studies have revealed inconsistent results complicating a sound interpretation of these findings. In the present study, we summarized the existing literature through a systematic search of articles. Meta-analyses were used to evaluate effect sizes of instructed downregulation strategies on common autonomic (electrodermal, respiratory, cardiovascular, and pupillometric) and electromyographic (corrugator activity, emotion-modulated startle) measures. Moderator analyses were conducted, with moderators including study design, emotion induction, control instruction and trial duration. We identified k = 78 studies each contributing multiple sub-samples and performed 23 meta-analyses for combinations of emotion regulation strategy and psychophysiological measure. Overall, results showed that effects of reappraisal and suppression on autonomic measures were highly inconsistent across studies with rather small mean effect sizes. Electromyography (startle and corrugator activity) showed medium effect sizes that were consistent across studies. Our findings highlight the diversity as well as the low level of standardization and comparability of research in this area. Significant moderation of effects by study design, trial duration, and control condition emphasizes the need for better standardization of methods. In addition, the small mean effect sizes resulting from our analyses on autonomic measures should be interpreted with caution. Findings corroborate the importance of multi-channel approaches.

Promoting long-term inhibition of human fear responses by non-invasive transcutaneous vagus nerve stimulation during extinction training

Inhibiting fear-related thoughts and defensive behaviors when they are no longer appropriate to the situation is a prerequisite for flexible and adaptive responding to changing environments. Such inhibition of defensive systems is mediated by ventromedial prefrontal cortex (vmPFC), limbic basolateral amygdala (BLA), and brain stem locus-coeruleus noradrenergic system (LC-NAs). Non-invasive, transcutaneous vagus nerve stimulation (tVNS) has shown to activate this circuit. Using a multiple-day single-cue fear conditioning and extinction paradigm, we investigated long-term effects of tVNS on inhibition of low-level amygdala modulated fear potentiated startle and cognitive risk assessments. We found that administration of tVNS during extinction training facilitated inhibition of fear potentiated startle responses and cognitive risk assessments, resulting in facilitated formation, consolidation and long-term recall of extinction memory, and prevention of the return of fear. These findings might indicate new ways to increase the efficacy of exposure-based treatments of anxiety disorders.

Making translation work: Harmonizing cross-species methodology in the behavioural neuroscience of Pavlovian fear conditioning

Translational neuroscience bridges insights from specific mechanisms in rodents to complex functions in humans and is key to advance our general understanding of central nervous function. A prime example of translational research is the study of cross-species mechanisms that underlie responding to learned threats, by employing Pavlovian fear conditioning protocols in rodents and humans. Hitherto, evidence for (and critique of) these cross-species comparisons in fear conditioning research was based on theoretical viewpoints. Here, we provide a perspective to substantiate these theoretical concepts with empirical considerations of cross-species methodology. This meta-research perspective is expected to foster cross-species comparability and reproducibility to ultimately facilitate successful transfer of results from basic science into clinical applications.

Modeling anxiety in healthy humans: a key intermediate bridge between basic and clinical sciences

Animal models of anxiety disorders are important for elucidating neurobiological defense mechanisms. However, animal models are limited when it comes to understanding the more complex processes of anxiety that are unique to humans (e.g., worry) and to screen new treatments. In this review, we outline how the Experimental Psychopathology approach, based on experimental models of anxiety in healthy subjects, can mitigate these limitations and complement research in animals. Experimental psychopathology can bridge basic research in animals and clinical studies, as well as guide and constrain hypotheses about the nature of psychopathology, treatment mechanisms, and treatment targets. This review begins with a brief review of the strengths and limitations of animal models before discussing the need for human models of anxiety, which are especially necessary to probe higher-order cognitive processes. This can be accomplished by combining anxiety-induction procedures with tasks that probe clinically relevant processes to identify neurocircuits that are potentially altered by anxiety. The review then discusses the validity of experimental psychopathology and introduces a methodological approach consisting of five steps: (1) select anxiety-relevant cognitive or behavioral operations and associated tasks, (2) identify the underlying neurocircuits supporting these operations in healthy controls, 3) examine the impact of experimental anxiety on the targeted operations in healthy controls, (4) utilize findings from step 3 to generate hypotheses about neurocircuit dysfunction in anxious patients, and 5) evaluate treatment mechanisms and screen novel treatments. This is followed by two concrete illustrations of this approach and suggestions for future studies.