Association between neural reactivity and startle reactivity to uncertain threat in two independent samples

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 interactive effects of different facets of threat uncertainty and cognitive load in shaping fear and anxiety responses

A large body of research indicates that exaggerated response to uncertainty of a future threat is at the core of anxiety and related disorders, underscoring the need for a better understanding of the underlying mechanisms. Although behavioral and neuroimaging studies have suggested a close relationship between uncertainty responses and cognitive control, little is known about what elements of uncertainty are more or less vulnerable to cognitive modulation in shaping aversive responses. Leveraging a novel paradigm, an n-back working memory task embedded within a modified threat-of-shock paradigm, we examined how the influences of different facets of uncertainty (i.e., occurrence and timing) on psychophysiological responses were modulated by cognitive load. Psychophysiological responses were assessed using the acoustic startle reflex. Replicating prior work, the effects of cognitive load and temporal unpredictability of threat on startle responses were evident. The effect of occurrence unpredictability appears to depend on other factors. Under low cognitive load, startle response was potentiated when both the occurrence and the timing of threat were predictable. Under high cognitive load, startle response was significantly reduced, especially when a threat context involves uncertainty in both temporal and probability domains. These observations provide a framework for refining the model of fear and anxiety and for understanding the etiology of psychological disorders characterized by maladaptive uncertainty responses.

Neuropsychology of Generalized Anxiety Disorder in Clinical Setting: A Systematic Evaluation

This research paper provides a systematic review of the neuropsychology of generalized anxiety disorder (GAD), examining relevant articles' methodologies and subject matter and highlighting key findings. It suggests potential cognitive deficits in GAD patients, such as subtle attention, executive function, and working memory deficiencies. It also discusses neural correlates of GAD, particularly the hyperactivity in the amygdala and insula, and the additional impact of comorbidity with other psychiatric disorders. The paper uses the PRISMA methodology and draws data from the PsycINFO, Scopus, PubMed, and Elsevier databases. Although the reviewed research has contributed to understanding GAD's cognitive and neural mechanisms, further research is required. Additionally, the paper mentions the clinical neuropsychology of GAD, including strategies and treatments, such as cognitive behavioral therapy (CBT), mindfulness, and medication. Lastly, the review identifies the limitations of the existing research and recommends future directions to enhance the understanding of GAD's underlying cognitive and neural mechanisms. The neural underpinnings of GAD encompass heightened activity within the amygdala and insula, which are brain regions implicated in processing adverse emotional reactions. Co-occurring psychiatric disorders, such as major depressive disorder (MDD), can also impact neuropsychological functioning. Additional investigation is warranted to better understand the intricate interplay between GAD, cognitive performance, and underlying neural processes.

Behavioral and brain reactivity to uncertain stress prospectively predicts binge drinking in youth

Prior studies show that individuals with alcohol use disorder exhibit exaggerated behavioral and brain reactivity to uncertain threats (U-threat). It is posited this brain-based factor emerges early in life and contributes to the onset and escalation of alcohol problems. However, no study to date has tested this theory using a longitudinal within-subjects design. Ninety-five young adults, ages 17-19, with minimal alcohol exposure and established risk factors for alcohol use disorder participated in this multi-session study with a 1-year tracking period. Startle eyeblink potentiation and brain activation were collected at separate baseline sessions during the well-validated No-Predictable-Unpredictable (NPU) threat-of-shock task designed to probe reactivity to U-threat and predictable threat (P-threat). Participants self-reported their drinking behavior over the past 90 days at baseline and one-year later. We fit a series of multilevel hurdle models to model the binary outcome of whether binge drinking occurred and the continuous outcome of number of binge drinking episodes. Zero-inflated binary submodels revealed that greater baseline startle reactivity, bilateral anterior insula (AIC) reactivity, and dorsal anterior cingulate cortex (dACC) reactivity to U-threat were associated with increased probability of binge drinking. There were no other associations between reactivity to U- and P-threat and probability of binge drinking and number of binging episodes. These results demonstrate that exaggerated reactivity to U-threat is a brain-based individual difference factor that connotes risk for problem drinking. These findings also add to a growing literature implicating AIC and dACC dysfunction in the pathophysiology of alcohol use disorder.

Acute orexin antagonism selectively modulates anticipatory anxiety in humans: implications for addiction and anxiety

Research indicates that heightened anticipatory anxiety underlies several forms of psychopathology. Anticipatory anxiety can be reliably and objectively measured in the laboratory using the No-Predictable-Unpredictable (NPU) threat paradigm. The NPU paradigm is an ideal research tool for the NIH 'Fast-Fail' approach of screening promising compounds and testing human target engagement. Evidence from preclinical studies suggests that the hypocretin/orexin (ORX) hypothalamic neuropeptide system is a potential means for modulating anticipatory anxiety and disrupting stress-related alcohol use. The current study tested this question using a psychophysiological probe of the ORX system in humans. We examined whether a single dose of suvorexant (SUV; 10 mg; dual ORX receptor antagonist) can effectively and selectively target a well-validated human laboratory index of exaggerated anticipatory anxiety using a within-subjects placebo-controlled design. A total of twenty-one volunteers completed two laboratory sessions during acute administration of 10 mg SUV or placebo. Across sessions, we administered the NPU paradigm probing sustained anticipatory anxiety and fear while startle eyeblink was recorded as an index of aversive reactivity. Questionnaires assessing mood states and subjective drug effects were also collected. Results indicated SUV was well-tolerated. Compared with placebo, SUV was associated with decreased startle reactivity during anticipatory anxiety but not fear or no-threat conditions. Therefore, SUV selectively and effectively reduced objective indicators of anticipatory anxiety in humans and engaged our laboratory target of psychopathology. ORX antagonism may be a promising strategy for modulating human anxiety and potentially, stress-related alcohol use.

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.

Neural correlates of predictable and unpredictable threat in internalizing psychopathology

Converging lines of evidence suggest that heightened responding to unpredictable threat may be an important neurobiological marker of internalizing psychopathology (IP). Prior data also indicate that aversive responding to uncertainty may be mediated by hyperactivation of several brain regions within the frontolimbic circuit, namely the anterior insula (aINS) and the dorsal anterior cingulate cortex (dACC). To date, however, the majority of this research has been focused on individual diagnoses and it is unclear whether abnormal neural reactivity to unpredictable threat is observed within heterogeneous, transdiagnostic IP patient populations, as theory would suggest. The aim of the current study was to therefore examine the neural correlates of temporally unpredictable (U) and predictable (P) threat in a sample of healthy controls (n = 24) and patients with a broad range of IP diagnoses (n = 51). We also examined whether symptom severity measures of fear and distress/misery dimensions correlated with neural reactivity to U- and P-threat. All participants completed a modified version of a well-validated threat-of-shock task during functional magnetic resonance imaging (fMRI). Across all participants, U- and P-threat elicited heightened activation in the aINS and brainstem, while P-threat alone also activated the dACC. Relative to healthy controls, patients displayed greater activation in the right aINS during U-threat, and greater right brainstem activation during P-threat. In addition, we found that brainstem activity during U-threat correlated with fear, but not distress/misery, psychopathology. Taken together, these preliminary results suggest that exaggerated aINS reactivity during U-threat and brainstem reactivity during P-threat may have the potential to become important transdiagnostic biomarkers of IP; however, future research efforts are needed to corroborate and expand the present findings.

The Future of Contextual Fear Learning for PTSD Research: A Methodological Review of Neuroimaging Studies

There has been a great deal of recent interest in human models of contextual fear learning, particularly due to the use of such paradigms for investigating neural mechanisms related to the etiology of posttraumatic stress disorder. However, the construct of "context" in fear conditioning research is broad, and the operational definitions and methods used to investigate contextual fear learning in humans are wide ranging and lack specificity, making it difficult to interpret findings about neural activity. Here we will review neuroimaging studies of contextual fear acquisition in humans. We will discuss the methodology associated with four broad categories of how contextual fear learning is manipulated in imaging studies (colored backgrounds, static picture backgrounds, virtual reality, and configural stimuli) and highlight findings for the primary neural circuitry involved in each paradigm. Additionally, we will offer methodological recommendations for human studies of contextual fear acquisition, including using stimuli that distinguish configural learning from discrete cue associations and clarifying how context is experimentally operationalized.

The Electrical Aftermath: Brain Signals of Posttraumatic Stress Disorder Filtered Through a Clinical Lens

This review aims to identify patterns of electrical signals identified using electroencephalography (EEG) linked to posttraumatic stress disorder (PTSD) diagnosis and symptom dimensions. We filter EEG findings through a clinical lens, evaluating nuances in findings according to study criteria and participant characteristics. Within the EEG frequency domain, greater right than left parietal asymmetry in alpha band power is the most promising marker of PTSD symptoms and is linked to exaggerated physiological arousal that may impair filtering of environmental distractors. The most consistent findings within the EEG time domain focused on event related potentials (ERPs) include: 1) exaggerated frontocentral responses (contingent negative variation, mismatch negativity, and P3a amplitudes) to task-irrelevant distractors, and 2) attenuated parietal responses (P3b amplitudes) to task-relevant target stimuli. These findings suggest that some individuals with PTSD suffer from attention dysregulation, which could contribute to problems concentrating on daily tasks and goals in lieu of threatening distractors. Future research investigating the utility of alpha asymmetry and frontoparietal ERPs as diagnostic and predictive biomarkers or intervention targets are recommended.

Association among anterior cingulate cortex volume, psychophysiological response, and PTSD diagnosis in a Veteran sample

Posttraumatic stress disorder (PTSD) is associated with fear response system dysregulation. Research has shown that the anterior cingulate cortex (ACC) may modulate the fear response and that individuals with PTSD have abnormalities in ACC structure and functioning. Our objective was to assess whether ACC volume moderates the relationship between PTSD and fear-potentiated psychophysiological response in a sample of Gulf War Veterans. 142 Veteran participants who were associated with a larger study associated with Gulf War Illness were exposed to no threat, ambiguous threat, and high threat conditions in a fear conditioned startle response paradigm and also provided MRI imaging data. PTSD was assessed using the Clinician Administered PTSD Scale (CAPS). Decreased caudal ACC volume predicted greater psychophysiological responses with a slower habituation of psychophysiological magnitudes across trials (p < 0.001). PTSD diagnosis interacted significantly with both caudal and rostral ACC volumes on psychophysiological response magnitudes, where participants with PTSD and smaller rostral and caudal ACC volumes had greater psychophysiological magnitudes across trials (p < 0.05 and p < 0.001, respectively) and threat conditions (p < 0.05 and p < 0.005). Our results suggest that ACC volume may moderate both threat sensitivity and threat response via impaired habituation in individuals who have been exposed to traumatic events. More research is needed to assess whether ACC size and these associated response patterns are due to neurological processes resulting from trauma exposure or if they are indicative of a premorbid risk for PTSD subsequent to trauma exposure.

The Affective and Neural Correlates of Heroin versus Cocaine Use in Addiction Are Influenced by Environmental Setting But in Opposite Directions

Previous studies have shown that individuals with heroin and cocaine addiction prefer to use these drugs in distinct settings: mostly at home in the case of heroin and mostly outside the home in the case of cocaine. Here we investigated whether the context would modulate the affective and neural responses to these drugs in a similar way. First, we used a novel emotional task to assess the affective state produced by heroin or cocaine in different settings, based on the recollections of male and female drug users. Then we used fMRI to monitor neural activity during drug imagery (re-creating the setting of drug use) in male drug users. Consistent with our working hypothesis, the majority of participants reported a shift in the affective valence of heroin from mostly pleasant at home to mostly unpleasant outside the home (p < 0.0001). The opposite shift was observed for cocaine; that is, most participants who found cocaine pleasant outside the home found it unpleasant when taken at home (p < 0.0014). Furthermore, we found a double dissociation, as a function of drug and setting imagery, in BOLD signal changes in the left PFC and caudate, and bilaterally in the cerebellum (all p values <0.01), suggesting that the fronto-striatal-cerebellar network is implicated in the contextualization of drug-induced affect. In summary, we report that the same setting can influence in opposite directions the affective and neural response to psychostimulants versus opiates in humans, adding to growing evidence of distinct substrates for the rewarding effects of these two drug classes.SIGNIFICANCE STATEMENT The rewarding effects of addictive drugs are often thought to depend on shared substrates. Yet, environmental influences can unmask striking differences between psychostimulants and opiates. Here we used emotional tasks and fMRI to explore the influence of setting on the response to heroin versus cocaine in individuals with addiction. Simply moving from one setting to another significantly decreased heroin pleasure but increased cocaine pleasure, and vice versa. Similar double dissociation was observed in the activity of the fronto-striatal-cerebellar network. These findings suggest that the effects of opiates and psychostimulants depend on dissociable psychological and neural substrates and that therapeutic approaches to addiction should take into account the peculiarities of different drug classes and the settings of drug use.

Error-related brain activity and internalizing disorder symptom dimensions in depression and anxiety

BACKGROUND

Research suggests that enhanced neural reactivity to errors, measured via the error-related negativity (ERN), is relatively unique to internalizing psychopathologies (IPs) and symptom clusters characterized by excessive worry and apprehension. However, no prior study has tested the association between the ERN and IP symptom dimensions in a heterogeneous, clinically representative patient population. The current study was designed to address this gap in the literature and clarify the role of the ERN in an adult IP treatment-seeking patient sample.

METHOD

Eighty-five participants completed a well-validated flanker task known to robustly elicit the ERN and a battery of questionnaires assessing a range of IP symptoms. All participants had at least one IP diagnosis and over 75% had co-occurring IPs. A principal components analysis (PCA) was performed on the questionnaire data indicating two distinct factors that characterized the IP sample: affective distress/misery and fear-based anxiety.

RESULTS

Analyses indicated that within this sample, an enhanced ERN, but not CRN, was associated with greater fear-based anxiety symptoms but had no relation with distress/misery symptoms.

CONCLUSIONS

Together, these findings indicate that an enhanced ERN may not be specific to worry/apprehension and may extend to the IP fear dimension. The results also converge with a broader literature suggesting that fear-based psychopathology is characterized by an exaggerated reactivity to threat and this objective, psychophysiological response tendency may distinguish fear disorders from distress.