How many blinks are necessary for a reliable startle response? A test using the NPU-threat task

Attenuation of Anxiety-Potentiated Startle After Treatment With Escitalopram or Mindfulness Meditation in Anxiety Disorders

BACKGROUND

Biological markers for anxiety disorders may further understanding of disorder pathophysiology and suggest potential targeted treatments. The fear-potentiated startle (FPS) (a measure of startle to predictable threat) and anxiety-potentiated startle (APS) (startle to unpredictable threat) laboratory paradigm has been used to detect physiological differences in individuals with anxiety disorders compared with nonanxious control individuals, and in pharmacological challenge studies in healthy adults. However, little is known about how startle may change with treatment for anxiety disorders, and no data are available regarding alterations due to mindfulness meditation training.

METHODS

Ninety-three individuals with anxiety disorders and 66 healthy individuals completed 2 sessions of the neutral, predictable, and unpredictable threat task, which employs a startle probe and the threat of shock to assess moment-by-moment fear and anxiety. Between the two testing sessions, patients received randomized 8-week treatment with either escitalopram or mindfulness-based stress reduction.

RESULTS

APS, but not FPS, was higher in participants with anxiety disorders compared with healthy control individuals at baseline. Further, there was a significantly greater decrease in APS for both treatment groups compared with the control group, with the patient groups showing reductions bringing them into the range of control individuals at the end of the treatment.

CONCLUSIONS

Both anxiety treatments (escitalopram and mindfulness-based stress reduction) reduced startle potentiation during unpredictable (APS) but not predictable (FPS) threat. These findings further validate APS as a biological correlate of pathological anxiety and provide physiological evidence for the impact of mindfulness-based stress reduction on anxiety disorders, suggesting that there may be comparable effects of the two treatments on anxiety neurocircuitry.

Threat effects on attention networks in individuals with a history of externalizing behaviors

Research identifying the biobehavioral processes that link threat exposure to cognitive alterations can inform treatments designed to reduce perpetration of stress-induced aggression. The present study attempted to specify the effects of relatively predictable versus unpredictable threat on two attention networks, attentional alerting and executive control. In a sample of adults (n = 74, 35 % identifying as women, Mage = 32.85) with high rates of externalizing behaviors (e.g., substance use, criminal/legal system involvement, aggressivity), we measured event-related brain activity during an attention network test that manipulated cognitive systems activation under relatively unpredictable and predictable threat conditions. Results showed that threat exposure alters attentional alerting and executive control. The predictable threat condition, relative to unpredictable threat, increased visual alerting (N1 amplitude to alert vs. no alert cue conditions) and decreased attention to the task (P3 amplitude to subsequent task-relevant flankers, but these effects did not survive adjusting for multiple tests. In contrast, overall threat and unpredictable threat conditions were associated with faster response time to alert cue (versus no cue) and poorer conflict processing, operationalized as flanker N2 reductions and slower response time to incongruent (versus congruent) flanker trials. These results expand what is known about threat-related modulation of cognition in a sample of individuals with histories of externalizing behaviors.

Continuous Theta Burst Stimulation to the Right Dorsolateral Prefrontal Cortex may increase Potentiated Startle in healthy individuals

Background

Convergent neuroimaging and neuromodulation studies implicate the right dorsolateral prefrontal cortex (dlPFC) as a key region involved in anxiety-cognition interactions. However, neuroimaging data are correlational, and neuromodulation studies often lack appropriate methodological controls. Accordingly, this work was designed to explore the role of right prefrontal cognitive control mechanisms in the expression/regulation of anxiety using continuous theta-burst transcranial magnetic stimulation (cTBS) and threat of unpredictable shock. Based on prior neuromodulation studies, we hypothesized that the right dlPFC contributed to anxiety expression, and that cTBS should downregulate this expression.

Methods

We measured potentiated startle and performance on the Sternberg working memory paradigm in 28 healthy participants before and after 4 sessions (600 pulses/session) of active or sham cTBS. Stimulation was individualized to the right dlPFC site of maximal working memory-related activity and optimized using electric-field modeling.

Results

Compared with sham cTBS, active cTBS, which is thought to induce long-term depression-like synaptic changes, increased startle during threat of shock, but the effect was similar for predictable and unpredictable threat. As a measure of target (dis)engagement, we also showed that active but not sham cTBS decreased accuracy on the Sternberg task.

Conclusions

Counter to our initial hypothesis, cTBS to the right dlPFC made individuals more anxious, rather than less anxious. Although preliminary, these results are unlikely to be due to transient effects of the stimulation, because anxiety was measured 24 hours after cTBS. In addition, these results are unlikely to be due to off-target effects, because target disengagement was evident from the Sternberg performance data.

Sustained threat and phasic fear in the laboratory and cognitive-emotional processes of anxiety in everyday life - An ambulatory assessment study

Fear is a phasic state of apprehension to an imminent threat, whereas anxiety is a more sustained state of expecting a potential threat leading to tension and worry. The NPU-threat test is a laboratory startle paradigm allowing a reliable and valid assessment of both, fear- and anxiety-potentiated reactions. It is suggested to differentiate between anxiety disorders, but little is known on associations with everyday life experiences of cognitive-emotional processes regarding anxiety in non-clinical samples. In the present project, the NPU-threat test was applied in three studies with (1) unselected healthy individuals, (2) participants with extreme manifestations of trait anxiety (low vs. high) and (3) individuals preparing for a high-stakes exam. Self-reported states of emotionality and worry were assessed during a four-day ambulatory assessment (AA). Overall, NPU-threat test measures did not significantly differ between studies, while the AA dependent measures were sufficiently sensitive to capture differences between groups. However, there was no significant association between psychophysiological measures of the NPU-threat test and AA state measures across participants. In participants recruited for low vs. high trait anxiety we found an association with AA worry and emotionality, but no interaction with potentiated startle. The present findings do not support the idea of a link between our laboratory biomarker and adaptive regulation of cognitive-emotional states in everyday life in healthy individuals. We speculate that an association between laboratory physiological measures and everyday experience of anxious states may be detectable in clinical samples.

Differential effects of the translocator protein 18 kDa (TSPO) ligand etifoxine and the benzodiazepine alprazolam on startle response to predictable threat in a NPU-threat task after acute and short-term treatment

RATIONALE

Benzodiazepines have been extensively investigated in experimental settings especially after single administration, which mostly revealed effects on unpredictable threat (U-threat) rather than predictable threat (P-threat). Given the need for pharmacological alternatives with a preferable side-effect profile and to better represent clinical conditions, research should cover also other anxiolytics and longer application times.

OBJECTIVES

The present study compared the acute and short-term effects of the translocator protein 18 kDa (TSPO) ligand etifoxine and the benzodiazepine alprazolam on P-threat and U-threat while controlling for sedation.

METHODS

Sixty healthy male volunteers, aged between 18 and 55 years, were randomly assigned to receive a daily dose of either 150 mg etifoxine, 1.5 mg alprazolam, or placebo for 5 days. On days 1 and 5 of intake, they performed a NPU-threat task including neutral (N), predictable (P), and unpredictable (U) conditions, while startle responsivity and self-reports were studied. Sedative effects were assessed using a continuous performance test.

RESULTS

Neither alprazolam nor etifoxine affected startle responsivity to U-threat on any of the testing days. While etifoxine reduced the startle response to P-threat on day 1 of treatment for transformed data, a contrary effect of alprazolam was found for raw values. No effects on self-reports and no evidence of sedation could be observed for either drug.

CONCLUSIONS

None of the anxiolytic substances had an impact on startle potentiation to U-threat even after several days of intake. The effects of the anxiolytics on startle responsivity to P-threat as well as implications for future studies are discussed.

Fear Potentiated Startle in Children With Autism Spectrum Disorder: Association With Anxiety Symptoms and Amygdala Volume

Atypical responses to fearful stimuli and the presence of various forms of anxiety are commonly seen in children with autism spectrum disorder (ASD). The fear potentiated startle paradigm (FPS), which has been studied both in relation to anxiety and as a probe for amygdala function, was carried out in 97 children aged 9-14 years including 48 (12 female) with ASD and 49 (14 female) with typical development (TD). In addition, exploratory analyses were conducted examining the association between FPS and amygdala volume as assessed with magnetic resonance imaging in a subset of the children with ASD with or without an anxiety disorder with available MRI data. While the startle latency was increased in the children with ASD, there was no group difference in FPS. FPS was not significantly associated with traditional Diagnostic and Statistical Manual (DSM) or "autism distinct" forms of anxiety. Within the autism group, FPS was negatively correlated with amygdala volume. Multiple regression analyses revealed that the association between FPS and anxiety severity was significantly moderated by the size of the amygdala, such that the association between FPS and anxiety was significantly more positive in children with larger amygdalas than smaller amygdalas. These findings highlight the heterogeneity of emotional reactivity associated with ASD and the difficulties in establishing biologically meaningful probes of altered brain function. LAY SUMMARY: Many children with autism spectrum disorder (ASD) have additional problems such as anxiety that can greatly impact their lives. How these co-occurring symptoms develop is not well understood. We studied the amygdala, a region of the brain critical for processing fear and a laboratory method called fear potentiated startle for measuring fear conditioning, in children with ASD (with and without an anxiety disorder) and typically developing children. Results showed that the connection between fear conditioning and anxiety is dependent on the size of the amygdala in children with ASD.

Implicit and explicit motivational responses to high- and low-calorie food in women with disordered eating

Eating disorders and their symptoms are thought to be associated with altered motivational responding to food. Binge eating may relate to increased reward reactivity, restrictive eating may be associated with increased threat and/or decreased reward reactivity, and the combination of these symptoms within an individual may be linked to motivational conflict to food. Using both implicit (i.e., physiological) and explicit (i.e., self-reported) measures, we tested these hypotheses in 88 women with binge eating only, restrictive eating only, both binge eating and restrictive eating, or no eating pathology. Participants viewed and rated high-calorie food, low-calorie food, and emotional images while startle eye blink and postauricular reflexes were measured. Arousal and craving, but not valence, ratings were significantly greater for high- than low-calorie food. Startle blink reflexes during all food images were significantly lower than during neutral images, whereas only high-calorie foods related to greater postauricular reactivity than neutral images. Eating pathology group did not predict implicit and explicit motivational reactions to food. Exploratory dimensional analyses revealed that rating low-calorie foods as lower on craving predicted endorsement of restrictive eating, while rating low-calorie foods as lower on valence and arousal, and experiencing lower postauricular reactivity to high-calorie foods minus neutral images, predicted greater frequency of restrictive eating episodes. Decreased implicit and explicit appetitive motivation to high- and low-calorie food may relate to the presence and frequency of restrictive eating. Future longitudinal research should investigate whether decreased appetitive responding to food is a risk factor for, versus consequence of, restrictive eating.

A way forward for anxiolytic drug development: Testing candidate anxiolytics with anxiety-potentiated startle in healthy humans

This review introduces a research strategy that may radically transform the pursuit of new anxiolytics, via the use of human models of anxiety in healthy individuals. Despite enormous investments in developing novel pharmacological treatments for anxiety disorders, pharmacotherapy for these conditions remains suboptimal. Most candidate anxiolytics from animal studies fail in clinical trials. We propose an additional screening step to help select candidate anxiolytics before launching clinical trials. This intermediate step moves the evidence for the potential anxiolytic property of candidate drugs from animals to humans, using experimental models of anxiety in healthy individuals. Anxiety-potentiated startle is a robust translational model of anxiety. The review of its face, construct, and predictive validity as well as its psychometric properties in humans establishes it as a promising tool for anxiolytic drug development. In conclusion, human models of anxiety may stir a faster, more efficient path for the development of clinically effective anxiolytics.

Mechanistic link between right prefrontal cortical activity and anxious arousal revealed using transcranial magnetic stimulation in healthy subjects

Much of the mechanistic research on anxiety focuses on subcortical structures such as the amygdala; however, less is known about the distributed cortical circuit that also contributes to anxiety expression. One way to learn about this circuit is to probe candidate regions using transcranial magnetic stimulation (TMS). In this study, we tested the involvement of the dorsolateral prefrontal cortex (dlPFC), in anxiety expression using 10 Hz repetitive TMS (rTMS). In a within-subject, crossover experiment, the study measured anxiety in healthy subjects before and after a session of 10 Hz rTMS to the right dorsolateral prefrontal cortex (dlPFC). It used threat of predictable and unpredictable shock to induce anxiety and anxiety potentiated startle to assess anxiety. Counter to our hypotheses, results showed an increase in anxiety-potentiated startle following active but not sham rTMS. These results suggest a mechanistic link between right dlPFC activity and physiological anxiety expression. This result supports current models of prefrontal asymmetry in affect, and lays the groundwork for further exploration into the cortical mechanisms mediating anxiety, which may lead to novel anxiety treatments.

Low-frequency parietal repetitive transcranial magnetic stimulation reduces fear and anxiety

Anxiety disorders are the most prevalent mental disorders, with few effective neuropharmacological treatments, making treatments development critical. While noninvasive neuromodulation can successfully treat depression, few treatment targets have been identified specifically for anxiety disorders. Previously, we showed that shock threat increases excitability and connectivity of the intraparietal sulcus (IPS). Here we tested the hypothesis that inhibitory repetitive transcranial magnetic stimulation (rTMS) targeting this region would reduce induced anxiety. Subjects were exposed to neutral, predictable, and unpredictable shock threat, while receiving double-blinded, 1 Hz active or sham IPS rTMS. We used global brain connectivity and electric-field modelling to define the single-subject targets. We assessed subjective anxiety with online ratings and physiological arousal with the startle reflex. Startle stimuli (103 dB white noise) probed fear and anxiety during the predictable (fear-potentiated startle, FPS) and unpredictable (anxiety-potentiated startle, APS) conditions. Active rTMS reduced both FPS and APS relative to both the sham and no stimulation conditions. However, the online anxiety ratings showed no difference between the stimulation conditions. These results were not dependent on the laterality of the stimulation, or the subjects' perception of the stimulation (i.e. active vs. sham). Results suggest that reducing IPS excitability during shock threat is sufficient to reduce physiological arousal related to both fear and anxiety, and are consistent with our previous research showing hyperexcitability in this region during threat. By extension, these results suggest that 1 Hz parietal stimulation may be an effective treatment for clinical anxiety, warranting future work in anxiety patients.

Startle during threat longitudinally predicts functional impairment independent of DSM diagnoses

Heightened responsivity to unpredictable, and perhaps predictable, threat characterizes some internalizing disorders and may be vulnerability factors for psychopathology as well. However, few studies have directly tested whether individual differences in unpredictable and/or predictable threat responding longitudinally predict symptoms of psychopathology and functional outcomes. Examining functioning is particularly important given that functioning is separable from symptoms of psychopathology. The present study examined whether electromyography startle measures of predictable and/or unpredictable threat responding was associated with interviewer-assessed symptoms of internalizing psychopathology and functional impairment at baseline (n = 409) and one-year follow-up (n = 104). Elevated startle responding to unpredictable and predictable threat longitudinally predicted a worsening of functioning over time and this effect was independent of change of symptoms over time. Importantly, threat responding at baseline predicted functional impairment during the follow-up independent of the effects of DSM-defined fear-based (e.g., panic disorder) or distress-misery (e.g., major depressive disorder) internalizing disorders. These findings provide initial support for the incremental validity of neurobiological vulnerability markers of threat responding over and above DSM disorders and highlight the importance of distinguishing functional outcomes from symptom outcomes.

The Impact of Alcohol and Social Context on the Startle Eyeblink Reflex

BACKGROUND

Researchers have long sought to understand how individuals respond to alcohol in social settings with the aim of elucidating pathways of risk for alcohol use disorder (AUD). But studies that incorporate a social context are still outnumbered by those that examine alcohol's subjective effects among participants drinking alcohol in isolation. Further, perhaps due to the challenges of capturing automatic affective processes in these settings, prior studies of alcohol response in social context have relied mainly on self-report measures, and so relatively little is known about alcohol's psychophysiological effects in social settings.

METHODS

Using a novel paradigm that integrated alcohol-administration procedures, startle methodology, and social context, this study examined the impact of alcohol and social context on startle eyeblink reflex among 40 social drinkers.

RESULTS

Results indicated that there was a significant effect of group presence, indicating that startle magnitude was larger when people were alone than with others. There was a significant group presence-by-alcoholic beverage interaction, with the effect of alcohol being significantly larger when people were alone versus with others. These effects were found both for the startle habituation data and during the picture-viewing task.

CONCLUSIONS

Results of this study highlight the importance of considering the presence of other individuals for understanding alcohol response and mechanisms of AUD risk. Findings are discussed in light of both emotional and cognitive correlates of startle reflex magnitude. Future research should examine these effects within larger samples of participants and further explore mechanisms that might underlie these effects.

Event-related potentials to threat of predictable and unpredictable shock

Cognitive affective neuroscience tasks that are straightforward to administer, measure key constructs of interest, and can be used in different lab settings and with multiple psychophysiological methods can lead to a more complete understanding of experimental effects. The no-threat, predictable threat, unpredictable threat (NPU-threat) task assesses constructs of interest to both clinical and basic affective science literatures, is relatively brief to administer, and has been used across labs with a number of different measurements (e.g., startle eyeblink, fMRI, corrugator response, subjective ratings). ERPs provide another means of assessing neurobiological reactivity during the NPU-threat task, but to date such measures have been underutilized. That is, no study has yet evaluated cue-elicited ERPs in the NPU-threat task. Here, cue-elicited ERPs were assessed in 78 participants who completed a version of the NPU-threat task previously shown to reliably moderate startle eyeblink amplitudes. Results showed larger P2 amplitudes for unpredictable versus predictable trials, increased P3s and late positive potentials for threatening versus no-threat trials, as well as larger stimulus preceding negativities for threatening versus no-threat trials (driven primarily by predictable threat cues). In line with prior work, we observed enhanced startle eyeblink for threatening versus no-threat trials and for unpredictable compared to predictable threat interstimulus intervals. In addition, the probe-elicited P3 was suppressed for predictable and unpredictable compared to no-threat trials. Therefore, cue-elicited ERPs, which can be recorded alongside other measures in the NPU-threat task (e.g., startle), may provide useful indices of temporally distinct stages of predictable and unpredictable threat processing.

The effect of panic disorder versus anxiety sensitivity on event-related potentials during anticipation of threat

Attention-related abnormalities are key components of the abnormal defensive responding observed in panic disorder (PD). Although behavioral studies have found aberrant attentional biases towards threat in PD, psychophysiological studies have been mixed. Predictability of threat, an important feature of threat processing, may have contributed to these mixed findings. Additionally, anxiety sensitivity, a dimensional trait associated with PD, may yield stronger associations with cognitive processes than categorical diagnoses of PD. In this study, 171 participants with PD and/or depression and healthy controls completed a task that differentiated anticipation of predictable vs. unpredictable shocks, while startle eyeblink and event-related potentials (ERPs [N100, P300]) were recorded. In all participants, relative to the control condition, probe N100 was enhanced to both predictable and unpredictable threat, whereas P300 suppression was unique to predictable threat. Probe N100, but not P300, was associated with startle eyeblink during both threatening conditions, and was strongest for unpredictable threat. PD was not associated with ERPs, but anxiety sensitivity (physical concerns) was positively associated with probe N100 (indicating reduced responding) in the unpredictable condition independent of PD diagnosis. Vulnerability to panic-related psychopathology may be characterized by aberrant early processing of threat, which may be especially evident during anticipation of unpredictable threats.

Using Event-Related Potentials and Startle to Evaluate Time Course in Anxiety and Depression

The National Institute of Mental Health's Research Domain Criteria initiative is a research framework designed toward understanding psychopathology as abnormalities of dimensional neurobehavioral constructs rather than in terms of DSM-defined categories. Research Domain Criteria constructs within the negative valence domain are particularly relevant for understanding anxiety and depressive disorders, which are pervasive, debilitating, and characterized by negative processing bias. One important direction for Research Domain Criteria research is investigating processes and parameters related to the time course (or chronometry) of negative valenced constructs. Two reliable methods for assessing chronometry are event-related potentials (ERPs) and startle blink. In this qualitative review, we examine ERP and startle studies of individuals with anxiety or depression or individuals vulnerable to affective disorders. The aim of the review is to highlight how these methods can inform the role of chronometry in the spectrum of anxiety and depression. ERP studies examining different chronometry facets of negative valenced responses have shown that transdiagnostic groups of individuals with internalizing psychopathologies exhibit abnormalities at early stages of processing. Startle reactivity studies have robustly differentiated fear-based disorders (e.g., panic disorder, social phobia) from other anxiety disorders (e.g., generalized anxiety disorder) and have also shown that different internalizing phenotypes exhibit different patterns of habituation. Findings lend support to the value of ERP and startle measures in identifying groups that cut across conventional classification systems. We also highlight methodological issues that can aid in the validity and reproducibility of ERP and startle findings and, ultimately, in the goal of developing more precise models of anxiety and depression.

Preliminary evidence that reactivity to uncertain threat is an endophenotype for alcohol use disorder

BACKGROUND

Having an exaggerated reactivity to threats that are uncertain (U-threat) may facilitate the initiation and maintenance of excessive alcohol use in some individuals. This abnormality may not just be a concomitant for alcohol use disorder (AUD), but also an endophenotype for AUD.

METHOD

The aim of the current study was therefore to provide a preliminary test of whether U-threat is an endophenotype for AUD using several of the endophenotype criteria outlined by Gottesman and Gould (2003). Specifically, the study examined whether heightened U-threat reactivity is evidenced in those with: 1) current AUD; 2) remitted AUD (early and sustained remission examined separately); and 3) at-risk for AUD by virtue of having a positive family history of AUD. Participants (N = 147) completed a well-validated threat-of-shock task and startle eyeblink potentiation was collected as an index of aversive responding. Individuals and all available first-degree family members were diagnosed using structured clinical interviews.

RESULTS

Individuals at-risk for AUD, with current AUD, and AUD in remission (both early and sustained) all displayed exaggerated reactivity to U-threat, but not predictable threat, compared with non-AUD controls. Moreover, there were no significant differences between the at-risk and any of the AUD groups indicating that exaggerated reactivity to U-threat is relatively state-independent and present regardless of current AUD disease status.

CONCLUSIONS

The findings together highlight that exaggerated reactivity to U-threat may be a promising endophenotype for AUD that can aid in the refinement of mechanistic AUD disease models.

Dissociating the physiological components of unconscious emotional responses

Conscious emotional processing is characterized by a coordinated set of responses across multiple physiological systems. Although emotional stimuli can evoke certain physiological responses even when they are suppressed from awareness, it is not known whether unconscious emotional responses comprise a similar constellation or are confined to specific systems. To compare physiological responses to emotional stimuli with and without awareness, we measured a range of responses while participants viewed positive, negative and neutral images that were accompanied by noise bursts to elicit startle reflexes. We measured four responses simultaneously - skin conductance and heart rate changes in response to the images themselves; and startle eye-blink and post-auricular reflexes in response to the noise bursts that occurred during image presentation. For half of the participants, the images were masked from awareness using continuous flash suppression. The aware group showed the expected pattern of response across physiological systems: emotional images (regardless of valence) evoked larger skin conductance responses (SCRs) and greater heart rate deceleration than neutral images, negative images enhanced eye-blink reflexes and positive images enhanced post-auricular reflexes. In contrast, we found a striking dissociation between measures for the unaware group: typical modulation of SCRs and post-auricular reflexes, but no modulation of heart rate deceleration or eye-blink reflexes. Our findings suggest that although some physiological systems respond to emotional stimuli presented outside of awareness, conscious emotional processing may be characterized by a broad and coordinated set of responses across systems.