Neural Mechanisms of Impaired Fear Inhibition in Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) can develop in some individuals who are exposed to an event that causes extreme fear, horror, or helplessness (APA, 1994). PTSD is a complex and heterogeneous disorder, which is often co-morbid with depression, substance abuse, and anxiety disorders such as panic or social phobia. Given this complexity, progress in the field can be greatly enhanced by focusing on phenotypes that are more proximal to the neurobiology of the disorder. Such neurobiological intermediate phenotypes can provide investigative tools to increase our understanding of the roots of the disorder and develop better prevention or intervention programs. In the present paper, we argue that the inhibition of fear responses is an intermediate phenotype that is related to both the neurocircuitry associated with the disorder, and is linked to its clinical symptoms. An advantage of focusing on fear inhibition is that the neurobiology of fear has been well investigated in animal models providing the necessary groundwork in understanding alterations. Furthermore, because many paradigms can be tested across species, fear inhibition is an ideal translational tool. Here we review both the behavioral tests and measures of fear inhibition and the related neurocircuitry in neuroimaging studies with both healthy and clinical samples

Tailoring therapeutic strategies for treating posttraumatic stress disorder symptom clusters

According to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, posttraumatic stress disorder (PTSD) is characterized by three major symptom clusters following an event that elicited fear, helplessness, or horror. This review will examine each symptom cluster of PTSD separately, giving case study examples of patients who exhibit a preponderance of a given symptom domain. We use a translational approach in describing the underlying neurobiology that is relevant to particular symptoms and treatment options, thus showing how clinical practice can benefit from current research. By focusing on symptom clusters, we provide a more specific view of individual patient’s clinical presentations, in order to better address treatment needs. Finally, the review will also address potential genetic approaches to treatment as another form of individualized treatment

Prospective Associations between Emotion Dysregulation and Fear-Potentiated Startle: The Moderating Effect of Respiratory Sinus Arrhythmia

Background: Emotion dysregulation has been implicated in the negative outcomes following trauma exposure. A proposed biomarker of emotion dysregulation, respiratory sinus arrhythmia (RSA), has demonstrated associations with trauma-related phenomena, such as the fear-potentiated startle (FPS) response. The current study aimed to examine the prospective association between emotion dysregulation and RSA and FPS several years following trauma exposure. Methods: Participants were 131 women exposed to a campus mass shooting on February 14, 2008. Pre-shooting emotion dysregulation was assessed in 2006-2008. Startle response, measured by orbicularis oculi electromyography (EMG), and RSA were gathered during an FPS paradigm conducted from 2012-2015. Results: No significant associations among emotion dysregulation, RSA, and FPS emerged among the full sample. However, emotion dysregulation predicted FPS during both acquisition ( = .54, p = .03) and extinction ( = .75, p <.01), but only among individuals with high resting RSA. Conclusions: Findings suggest that pre-shooting emotion dysregulation is a potent predictor of FPS several years following potential trauma exposure, and this association varies by RSA level. Results emphasize the importance of examining autonomic regulation in the association between emotion dysregulation and recovery from trauma exposure

Generalization of fear-potentiated startle in the presence of auditory cues: a parametric analysis

Intense fear responses observed in trauma-, stressor-, and anxiety-related disorders can be elicited by a wide range of stimuli similar to those that were present during the traumatic event. The present study investigated the experimental utility of fear-potentiated startle paradigms to study this phenomenon, known as stimulus generalization, in healthy volunteers. Fear-potentiated startle refers to a relative increase in the acoustic startle response to a previously neutral stimulus that has been paired with an aversive stimulus. Specifically, in Experiment 1 an auditory pure tone (500 Hz) was used as the conditioned stimulus (CS+) and was reinforced with an unconditioned stimulus (US), an airblast to the larynx. A distinct tone (4000 Hz) was used as the nonreinforced stimulus (CS-) and was never paired with an airblast. Twenty-four hours later subjects underwent Re-training followed by a Generalization test, during which subjects were exposed to a range of generalization stimuli (250, 1000, 2000, 4000, 8000 Hz). In order to further examine the point at which fear no longer generalizes, a follow-up experiment (Experiment 2) was performed where a 4000 Hz pure tone was used as the CS+, and during the Generalization test, 2000 and 8000 Hz were used as generalization stimuli. In both Experiment 1 and 2 there was significant discrimination in US expectancy responses on all stimuli during the Generalization Test, indicating the stimuli were perceptually distinct. In Experiment 1, participants showed similar levels of fear-potentiated startle to the generalization stimuli that were adjacent to the CS+, and discriminated between stimuli that were 2 or more degrees from the CS+. Experiment 2 demonstrated no fear-potentiated startle generalization. The current study is the first to use auditory cues to test generalization of conditioned fear responses; such cues may be especially relevant to combat PTSD where much of the traumatic exposure may involve sounds

Catecholamine responses to virtual combat: implications for post-traumatic stress and dimensions of functioning

PTSD symptoms can result in functional impairment among service members (SMs), even in those without a clinical diagnosis. The variability in outcomes may be related to underlying catecholamine mechanisms. Individuals with PTSD tend to have elevated basal catecholamine levels, though less is known regarding catecholamine responses to trauma-related stimuli. We assessed whether catecholamine responses to a virtual combat environment impact the relationship between PTSD symptom clusters and elements of functioning. Eighty-seven clinically healthy SMs, within 2 months after deployment to Iraq or Afghanistan, completed self-report measures, viewed virtual-reality (VR) combat sequences, and had sequential blood draws. Norepinephrine responses to VR combat exposure moderated the relationship between avoidance symptoms and scales of functioning including physical functioning, physical-role functioning, and vitality. Among those with high levels of avoidance, norepinephrine change was inversely associated with functional status, whereas a positive correlation was observed for those with low levels of avoidance. Our findings represent a novel use of a virtual environment to display combat-related stimuli to returning SMs to elucidate mind-body connections inherent in their responses. The insight gained improves our understanding of post-deployment symptoms and quality of life in SMs and may facilitate enhancements in treatment. Further research is needed to validate these findings in other populations and to define the implications for treatment effectiveness

2,6-Disubstituted Piperidines as Modulators of Nicotinic Acetylcholine Receptor Mediated Neurotransmitter Release, Uptake and Storage

Compounds used for treating dependence on or withdrawal from a drug of abuse, for an eating disorder or for a CNS disease or pathology . . . To see the remainder of this abstract, please download this patent

Reduced Neural Activation During an Inhibition Task is Associated with Impaired Fear Inhibition in a Traumatized Civilian Sample

Introduction: Impaired inhibition of fear in the presence of safety cues and a deficiency in the extinction of fear cues are increasingly thought to be important biological markers of Posttraumatic Stress Disorder (PTSD). Other studies have suggested that there may be altered neural activation during behavioral inhibition tasks in subjects with PTSD. The current study aimed to see whether neural activation during inhibition was reduced in a highly traumatized civilian population, and whether atypical activation was associated with impaired fear inhibition. Methods: The participants were 41 traumatized women (20 PTSD+, 21 PTSD-) recruited from Grady Memorial Hospital in Atlanta, GA. We used a Go/NoGo procedure with functional magnetic resonance imaging (fMRI) in a high-resolution 3T scanner. Participants were instructed to press a button whenever an “X” or “O” appeared on the screen, but not if a red square appeared behind the letter. Participants were assessed for trauma history and PTSD diagnosis, and completed a fear-potentiated startle and extinction paradigm. Results: We found stronger activation in the ventromedial prefrontal cortex (vmPFC) in traumatized subjects without PTSD compared to those with PTSD in the NoGo greater than Go contrast condition. Activation in the vmPFC was negatively correlated with fear-potentiated startle responses during safety signal learning (p=.02) and fear extinction (p=.0002). Conclusions: These results contribute to understanding of how the neural circuitry involved in inhibitory processes may be deficient in PTSD. Furthermore, the same circuits involved in behavioral inhibition appear to be involved in fear inhibition processes during differential fear conditioning and extinction

Attention Bias Toward Threat is Associated with Exaggerated Fear Expression and Impaired Extinction in PTSD

Background: Post-traumatic stress disorder (PTSD) develops in a minority of traumatized individuals. Attention biases to threat and abnormalities in fear learning and extinction are processes likely to play a critical role in the creation and/or maintenance of PTSD symptomatology. However, the relationship between these processes has not been established, particularly in highly traumatized populations; understanding their interaction can help inform neural network models and treatments for PTSD. Method: Attention biases were measured using a dot probe task modified for use with our population; task stimuli included photographs of angry facial expressions, which are emotionally salient threat signals. A fear-potentiated startle paradigm was employed to measure atypical physiological response during acquisition and extinction phases of fear learning. These measures were administered to a sample of 64 minority (largely African American), highly traumatized individuals with and without PTSD. Results: Participants with PTSD demonstrated attention biases toward threat ; this attentional style was associated with exaggerated startle response during fear learning and early and middle phases of extinction, even after accounting for the effects of trauma exposure. Conclusions: Our findings indicate that an attentional bias toward threat is associated with abnormalities in ‘fear load’ in PTSD, providing seminal evidence for an interaction between these two processes. Future research combining these behavioral and psychophysiological techniques with neuroimaging will be useful toward addressing how one process may modulate the other and understanding whether these phenomena are manifestations of dysfunction within a shared neural network. Ultimately, this may serve to inform PTSD treatments specifically designed to correct these atypical processes

Versatility of Fear-Potentiated Startle Paradigms for Assessing Human Conditioned Fear Extinction and Return of Fear

Fear conditioning methodologies have often been employed as testable models for assessing learned fear responses in individuals with anxiety disorders such as post-traumatic stress disorder (PTSD) and specific phobia. One frequently used paradigm is measurement of the acoustic startle reflex under conditions that mimic anxiogenic and fear-related conditions. For example, fear-potentiated startle is the relative increase in the frequency or magnitude of the acoustic startle reflex in the presence of a previously neutral cue (e.g., colored shape; termed the conditioned stimulus or CS+) that has been repeatedly paired with an aversive unconditioned stimulus (e.g., airblast to the larynx). Our group has recently used fear-potentiated startle paradigms to demonstrate impaired fear extinction in civilian and combat populations with PTSD. In the current study, we examined the use of either auditory or visual CSs in a fear extinction protocol that we have validated and applied to human clinical conditions. This represents an important translational bridge in that numerous animal studies of fear extinction, upon which much of the human work is based, have employed the use of auditory CSs as opposed to visual CSs. Participants in both the auditory and visual groups displayed robust fear-potentiated startle to the CS+, clear discrimination between the reinforced CS+ and non-reinforced CS−, significant extinction to the previously reinforced CS+, and marked spontaneous recovery. We discuss the current results as they relate to future investigations of PTSD-related impairments in fear processing in populations with diverse medical and psychiatric histories

Impact of acute stress, sex, and childhood maltreatment on fear learning and fear generalization in a fear-potentiated startle paradigm

Many researchers approach the etiology of trauma-, stressor-, and anxiety-related mental disorders from the perspective of classical conditioning processes gone awry. According to this view, abnormal associative relationships between conditioned and unconditioned stimuli may underlie pathological anxiety and result in unusually intense fear memories or fear memories that cannot be properly extinguished. Recent work has expanded on this view by showing that many psychological disorders involving pathological anxiety are associated with an exaggerated form of stimulus generalization, leading individuals with such disorders to respond with fear and anxiety to a variety of contexts and cues that should not be threatening. It is well-known that stress, biological sex, childhood maltreatment, and certain dispositional factors can increase one’s susceptibility for pathological anxiety and significantly impact fear learning; thus, it is possible that these factors, alone or in combination, contribute to clinical anxiety by influencing fear generalization processes. In the present study, 478 healthy undergraduate students were exposed to the socially-evaluated cold pressor test immediately or 30 min prior to learning to associate one geometrical shape, but not another, with an aversive stimulus in a fear-potentiated startle paradigm. The next day, participants were tested for fear generalization by measuring their fear responses to a variety of stimuli that were similar to, but different from, the shapes observed on Day 1. Objective and subjective measures of stress were collected on Day 1, and childhood maltreatment was quantified with the Childhood Trauma Questionnaire. The results revealed that, across both stress time points, greater heart rate and greater cortisol levels in response to stress were associated with weaker fear acquisition and a flatter generalization gradient. These effects were influenced by participant sex and trait anxiety. We also found evidence to suggest that greater childhood maltreatment was associated with impaired fear acquisition in males but enhanced fear acquisition in females. These findings reveal a complex interaction between acute stress, biological sex, childhood maltreatment, dispositional anxiety, and fear learning that may lend insight into the etiology of certain stress-related psychological disorders