Altered processing of contextual information during fear extinction in PTSD: an fMRI study

Neural circuits in anxiety and stress disorders: a focused review

Anxiety and stress disorders are among the most prevalent neuropsychiatric disorders. In recent years, multiple studies have examined brain regions and networks involved in anxiety symptomatology in an effort to better understand the mechanisms involved and to develop more effective treatments. However, much remains unknown regarding the specific abnormalities and interactions between networks of regions underlying anxiety disorder presentations. We examined recent neuroimaging literature that aims to identify neural mechanisms underlying anxiety, searching for patterns of neural dysfunction that might be specific to different anxiety disorder categories. Across different anxiety and stress disorders, patterns of hyperactivation in emotion-generating regions and hypoactivation in prefrontal/regulatory regions are common in the literature. Interestingly, evidence of differential patterns is also emerging, such that within a spectrum of disorders ranging from more fear-based to more anxiety-based, greater involvement of emotion-generating regions is reported in panic disorder and specific phobia, and greater involvement of prefrontal regions is reported in generalized anxiety disorder and posttraumatic stress disorder. We summarize the pertinent literature and suggest areas for continued investigation.

Systems biology approach to understanding post-traumatic stress disorder

This review paper presents known biological facts about PTSD and the mathematical/systems biology tools used to understand the underpinning molecular principles.

On the Road to Translation for PTSD Treatment: Theoretical and Practical Considerations of the Use of Human Models of Conditioned Fear for Drug Development

The use of quantitative, laboratory-based measures of threat in humans for proof-of-concept studies and target development for novel drug discovery has grown tremendously in the last 2 decades. In particular, in the field of posttraumatic stress disorder (PTSD), human models of fear conditioning have been critical in shaping our theoretical understanding of fear processes and importantly, validating findings from animal models of the neural substrates and signaling pathways required for these complex processes. Here, we will review the use of laboratory-based measures of fear processes in humans including cued and contextual conditioning, generalization, extinction, reconsolidation, and reinstatement to develop novel drug treatments for PTSD. We will primarily focus on recent advances in using behavioral and physiological measures of fear, discussing their sensitivity as biobehavioral markers of PTSD symptoms, their response to known and novel PTSD treatments, and in the case of d-cycloserine, how well these findings have translated to outcomes in clinical trials. We will highlight some gaps in the literature and needs for future research, discuss benefits and limitations of these outcome measures in designing proof-of-concept trials, and offer practical guidelines on design and interpretation when using these fear models for drug discovery.

The effect of chronic phenytoin administration on single prolonged stress induced extinction retention deficits and glucocorticoid upregulation in the rat medial prefrontal cortex

RATIONALE

Post-traumatic stress disorder (PTSD) is a chronic, debilitating disorder. Only two pharmacological agents are approved for PTSD treatment, and they often do not address the full range of symptoms nor are they equally effective in all cases. Animal models of PTSD are critical for understanding the neurobiology involved and for identification of novel therapeutic targets. Using the rodent PTSD model, single prolonged stress (SPS), we have implicated aberrant excitatory neural transmission and glucocorticoid receptor (GR) upregulation in the medial prefrontal cortex (mPFC) and hippocampus (HPC) in fear memory abnormalities associated with PTSD.

OBJECTIVE

The objective of this study is to examine the potential protective effect of antiepileptic phenytoin (PHE) administration on SPS-induced extinction retention deficits and GR expression.

METHODS

Forty-eight SPS-treated male Sprague Dawley rats or controls were administered PHE (40, 20 mg/kg, vehicle) for 7 days following SPS stressors; then, fear conditioning, extinction, and extinction retention were tested.

RESULTS

Fear conditioning and extinction were unaffected by SPS or PHE, but SPS impaired extinction retention, and both doses of PHE rescued this impairment. Similarly, SPS increased GR expression in the mPFC and dorsal HPC, and PHE prevented SPS-induced GR upregulation in the mPFC.

CONCLUSIONS

These data demonstrate that PHE administration can prevent the development of extinction retention deficits and upregulation of GR. PHE exerts inhibitory effects on voltage-gated sodium channels and decreases excitatory neural transmission via glutamate antagonism. If glutamate hyperactivity in the days following SPS contributes to SPS-induced deficits, then these data may suggest that the glutamatergic system constitutes a target for secondary prevention.

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

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

Toward a translational approach to targeting the endocannabinoid system in posttraumatic stress disorder: a critical review of preclinical research

Despite the lack of clinical research, marijuana and synthetic cannabinoids have been approved to treat posttraumatic stress disorder (PTSD) in several states in the United States. This review critically examines preclinical research on the endocannabinoid system (ECS) in order to evaluate three key questions that are relevant to PTSD: (1) Does ECS dysfunction impact fear extinction? (2) Can stress-related symptoms be prevented by ECS modulation? (3) Is the ECS a potential target for enhancing PTSD treatment? Disruption of the ECS impaired fear extinction in rodents, and ECS abnormalities have been observed in PTSD. Targeting fear memories via the ECS had mixed results in rodents, whereas augmented cannabinoid receptor activation typically facilitated extinction. However, the translational value of these findings is limited by the paucity and inconsistency of human research. Further investigation is necessary to determine whether incorporating cannabinoids in treatment would benefit individuals with PTSD, with cautious attention to risks.

Prefrontal neuronal circuits of contextual fear conditioning

Over the past years, numerous studies have provided a clear understanding of the neuronal circuits and mechanisms involved in the formation, expression and extinction phases of conditioned cued fear memories. Yet, despite a strong clinical interest, a detailed understanding of these memory phases for contextual fear memories is still missing. Besides the well-known role of the hippocampus in encoding contextual fear behavior, growing evidence indicates that specific regions of the medial prefrontal cortex differentially regulate contextual fear acquisition and storage in both animals and humans that ultimately leads to expression of contextual fear memories. In this review, we provide a detailed description of the recent literature on the role of distinct prefrontal subregions in contextual fear behavior and provide a working model of the neuronal circuits involved in the acquisition, expression and generalization of contextual fear memories.

Focal and aberrant prefrontal engagement during emotion regulation in veterans with posttraumatic stress disorder

BACKGROUND

Collectively, functional neuroimaging studies implicate frontal-limbic dysfunction in the pathophysiology of posttraumatic stress disorder (PTSD), as reflected by altered amygdala reactivity and deficient prefrontal responses. These neural patterns are often elicited by social signals of threat (fearful/angry faces) and traumatic reminders (combat sounds, script-driven imagery). Although PTSD can be conceptualized as a disorder of emotion dysregulation, few studies to date have directly investigated the neural correlates of volitional attempts at regulating negative affect in PTSD.

METHODS

Using functional magnetic resonance imaging and a well-validated task involving cognitive regulation of negative affect via reappraisal and known to engage prefrontal cortical regions, the authors compared brain activation in veterans with PTSD (n = 21) and without PTSD (n = 21, combat-exposed controls/CEC), following military combat trauma experience during deployments in Afghanistan or Iraq. The primary outcome measure was brain activation during cognitive reappraisal (i.e., decrease negative affect) as compared to passive viewing (i.e., maintain negative affect) of emotionally evocative content of aversive images

RESULTS

The subjects in both groups reported similar successful reduction in negative affect following reappraisal. The PTSD group engaged the dorsolateral prefrontal cortex (dlPFC) during cognitive reappraisal, albeit to a lesser extent than the CEC group. Although the amygdala was engaged in both groups during passive viewing of aversive images, neither group exhibited attenuation of amygdala activation during cognitive reappraisal.

CONCLUSIONS

Veterans with combat-related PTSD showed less recruitment of the dlPFC involved in cognitive reappraisal, suggesting focal and aberrant neural activation during volitional, self-regulation of negative affective states.

Illuminating circuitry relevant to psychiatric disorders with optogenetics

The brain's remarkable capacity to generate cognition and behavior is mediated by an extraordinarily complex set of neural interactions that remain largely mysterious. This complexity poses a significant challenge in developing therapeutic interventions to ameliorate psychiatric disease. Accordingly, few new classes of drugs have been made available for patients with mental illness since the 1950s. Optogenetics offers the ability to selectively manipulate individual neural circuit elements that underlie disease-relevant behaviors and is currently accelerating the pace of preclinical research into neurobiological mechanisms of disease. In this review, we highlight recent findings from studies that employ optogenetic approaches to gain insight into normal and aberrant brain function relevant to mental illness. Emerging data from these efforts offers an exquisitely detailed picture of disease-relevant neural circuits in action, and hints at the potential of optogenetics to open up entirely new avenues in the treatment of psychiatric disorders.

Impaired right inferior frontal gyrus response to contextual cues in male veterans with PTSD during response inhibition

BACKGROUND

Posttraumatic stress disorder (PTSD) is often associated with impaired fear inhibition and decreased safety cue processing; however, studies capturing the cognitive aspect of inhibition and contextual cue processing are limited. In this fMRI study, the role of contextual cues in response inhibition was investigated.

METHODS

Male medication-naive war veterans with PTSD, male control veterans (combat controls) and healthy nonmilitary men (healthy controls) underwent fMRI while performing the stop-signal anticipation task (SSAT). The SSAT evokes 2 forms of response inhibition: reactive inhibition (outright stopping) and proactive inhibition (anticipation of stopping based on contextual cues).

RESULTS

We enrolled 28 veterans with PTSD, 26 combat controls and 25 healthy controls in our study. Reduced reactive inhibition was observed in all veterans, both with and without PTSD, but not in nonmilitary controls, whereas decreased inhibition of the left pre/postcentral gyrus appeared to be specifically associated with PTSD. Impaired behavioural proactive inhibition was also specific to PTSD. Furthermore, the PTSD group showed a reduced right inferior frontal gyrus response during proactive inhibition compared with the combat control group.

LIMITATIONS

Most patients with PTSD had comorbid psychiatric disorders, but such comorbidity is common in patients with PTSD. Also, the education level (estimate of intelligence) of participants, but not of their parents, differed among the groups.

CONCLUSION

Our findings of reduced proactive inhibition imply that patients with PTSD show reduced contextual cue processing. These results complement previous findings on fear inhibition and demonstrate that contextual cue processing in patients with PTSD is also reduced during cognitive processes, indicating a more general deficit.

From Pavlov to PTSD: the extinction of conditioned fear in rodents, humans, and anxiety disorders

Nearly 100 years ago, Ivan Pavlov demonstrated that dogs could learn to use a neutral cue to predict a biologically relevant event: after repeated predictive pairings, Pavlov's dogs were conditioned to anticipate food at the sound of a bell, which caused them to salivate. Like sustenance, danger is biologically relevant, and neutral cues can take on great salience when they predict a threat to survival. In anxiety disorders such as posttraumatic stress disorder (PTSD), this type of conditioned fear fails to extinguish, and reminders of traumatic events can cause pathological conditioned fear responses for decades after danger has passed. In this review, we use fear conditioning and extinction studies to draw a direct line from Pavlov to PTSD and other anxiety disorders. We explain how rodent studies have informed neuroimaging studies of healthy humans and humans with PTSD. We describe several genes that have been linked to both PTSD and fear conditioning and extinction and explain how abnormalities in fear conditioning or extinction may reflect a general biomarker of anxiety disorders. Finally, we explore drug and neuromodulation treatments that may enhance therapeutic extinction in anxiety disorders.

Resting state functional connectivity of the anterior cingulate cortex in veterans with and without post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is an anxiety disorder that is associated with structural and functional alterations in several brain areas, including the anterior cingulate cortex (ACC). Here, we examine resting state functional connectivity of ACC subdivisions in PTSD, using a seed-based approach. Resting state magnetic resonance images were obtained from male veterans with (n = 31) and without (n = 25) PTSD, and healthy male civilian controls (n = 25). Veterans with and without PTSD (combat controls) had reduced functional connectivity compared to healthy controls between the caudal ACC and the precentral gyrus, and between the perigenual ACC and the superior medial gyrus and middle temporal gyrus. Combat controls had increased connectivity between the rostral ACC and precentral/middle frontal gyrus compared to PTSD patients and healthy civilian controls. The resting state functional connectivity differences in the perigenual ACC network reported here indicate that veterans differ from healthy controls, potentially due to military training, deployment, and/or trauma exposure. In addition, specific alterations in the combat controls may potentially be related to resilience. These results underline the importance of distinguishing trauma-exposed (combat) controls from healthy civilian controls when studying PTSD.

Developing neuroimaging phenotypes of the default mode network in PTSD: integrating the resting state, working memory, and structural connectivity

Complementary structural and functional neuroimaging techniques used to examine the Default Mode Network (DMN) could potentially improve assessments of psychiatric illness severity and provide added validity to the clinical diagnostic process. Recent neuroimaging research suggests that DMN processes may be disrupted in a number of stress-related psychiatric illnesses, such as posttraumatic stress disorder (PTSD). Although specific DMN functions remain under investigation, it is generally thought to be involved in introspection and self-processing. In healthy individuals it exhibits greatest activity during periods of rest, with less activity, observed as deactivation, during cognitive tasks, e.g., working memory. This network consists of the medial prefrontal cortex, posterior cingulate cortex/precuneus, lateral parietal cortices and medial temporal regions. Multiple functional and structural imaging approaches have been developed to study the DMN. These have unprecedented potential to further the understanding of the function and dysfunction of this network. Functional approaches, such as the evaluation of resting state connectivity and task-induced deactivation, have excellent potential to identify targeted neurocognitive and neuroaffective (functional) diagnostic markers and may indicate illness severity and prognosis with increased accuracy or specificity. Structural approaches, such as evaluation of morphometry and connectivity, may provide unique markers of etiology and long-term outcomes. Combined, functional and structural methods provide strong multimodal, complementary and synergistic approaches to develop valid DMN-based imaging phenotypes in stress-related psychiatric conditions. This protocol aims to integrate these methods to investigate DMN structure and function in PTSD, relating findings to illness severity and relevant clinical factors.

Maximizing exposure therapy: an inhibitory learning approach

Exposure therapy is an effective approach for treating anxiety disorders, although a substantial number of individuals fail to benefit or experience a return of fear after treatment. Research suggests that anxious individuals show deficits in the mechanisms believed to underlie exposure therapy, such as inhibitory learning. Targeting these processes may help improve the efficacy of exposure-based procedures. Although evidence supports an inhibitory learning model of extinction, there has been little discussion of how to implement this model in clinical practice. The primary aim of this paper is to provide examples to clinicians for how to apply this model to optimize exposure therapy with anxious clients, in ways that distinguish it from a 'fear habituation' approach and 'belief disconfirmation' approach within standard cognitive-behavior therapy. Exposure optimization strategies include (1) expectancy violation, (2) deepened extinction, (3) occasional reinforced extinction, (4) removal of safety signals, (5) variability, (6) retrieval cues, (7) multiple contexts, and (8) affect labeling. Case studies illustrate methods of applying these techniques with a variety of anxiety disorders, including obsessive-compulsive disorder, posttraumatic stress disorder, social phobia, specific phobia, and panic disorder.

Inhibition of projections from the basolateral amygdala to the entorhinal cortex disrupts the acquisition of contextual fear

The development of excessive fear and/or stress responses to environmental cues such as contexts associated with a traumatic event is a hallmark of post-traumatic stress disorder (PTSD). The basolateral amygdala (BLA) has been implicated as a key structure mediating contextual fear conditioning. In addition, the hippocampus has an integral role in the encoding and processing of contexts associated with strong, salient stimuli such as fear. Given that both the BLA and hippocampus play an important role in the regulation of contextual fear conditioning, examining the functional connectivity between these two structures may elucidate a role for this pathway in the development of PTSD. Here, we used optogenetic strategies to demonstrate that the BLA sends a strong glutamatergic projection to the hippocampal formation through the entorhinal cortex (EC). Next, we photoinhibited glutamatergic fibers from the BLA terminating in the EC during the acquisition or expression of contextual fear conditioning. In mice that received optical inhibition of the BLA-to-EC pathway during the acquisition session, we observed a significant decrease in freezing behavior in a context re-exposure session. In contrast, we observed no differences in freezing behavior in mice that were only photoinhibited during the context re-exposure session. These data demonstrate an important role for the BLA-to-EC glutamatergic pathway in the acquisition of contextual fear conditioning.

Interactions of time of day and sleep with between-session habituation and extinction memory in young adult males

Within-session habituation and extinction learning co-occur as do subsequent consolidation of habituation (i.e., between-session habituation) and extinction memory. We sought to determine whether, as we predicted: (1) between-session habituation is greater across a night of sleep versus a day awake; (2) time-of-day accounts for differences; (3) between-session habituation predicts consolidation of extinction memory; (4) sleep predicts between-session habituation and/or extinction memory. Participants (N = 28) completed 4-5 sessions alternating between mornings and evenings over 3 successive days (2 nights) with session 1 in either the morning (N = 13) or evening (N = 15). Twelve participants underwent laboratory polysomnography. During 4 sessions, participants completed a loud-tone habituation protocol, while skin conductance response (SCR), blink startle electromyography (EMG), heart-rate acceleration and heart-rate deceleration (HRD) were recorded. For sessions 1 and 2, between-session habituation of EMG, SCR and HRD was greater across sleep. SCR and HRD were generally lower in the morning. Between-session habituation of SCR for sessions 1 and 2 was positively related to intervening (first night) slow wave sleep. In the evening before night 2, participants also underwent fear conditioning and extinction learning phases of a second protocol. Extinction recall was tested the following morning. Extinction recall was predicted only by between-session habituation of SCR across the same night (second night) and by intervening REM. We conclude that: (1) sleep augments between-session habituation, as does morning testing; (2) extinction recall is predicted by concurrent between-session habituation; and (3) both phenomena may be influenced by sleep.

Device-based brain stimulation to augment fear extinction: implications for PTSD treatment and beyond

Conditioned fear acquisition and extinction paradigms have been widely used both in animals and humans to examine the neurobiology of emotional memory. Studies have also shown that patients suffering from posttraumatic stress disorder (PTSD) exhibit deficient extinction recall along with dysfunctional activation of the fear extinction network, including the ventromedial prefrontal cortex, amygdala, and hippocampus. A great deal of overlap exists between this fear extinction network and brain regions associated with symptom severity in PTSD. This suggests that the neural nodes of fear extinction could be targeted to reduce behavioral deficits that may subsequently translate into symptom improvement. In this article, we discuss potential applications of brain stimulation and neuromodulation methods, which, combined with a mechanistic understanding of the neurobiology of fear extinction, could be used to further our understanding of the pathophysiology of anxiety disorders and develop novel therapeutic tools. To this end, we discuss the following stimulation approaches: deep-brain stimulation, vagus nerve stimulation, transcranial direct current stimulation, and transcranial magnetic stimulation. We propose new translational research avenues that, from a systems neuroscience perspective, aim to expand our understanding of circuit dynamics and fear processing toward the practical development of clinical tools, to be used alone or in combination with behavioral therapies.

Cortico-limbic responses to masked affective faces across ptsd, panic disorder, and specific phobia

BACKGROUND

Exaggerated amygdala and reduced ventromedial prefrontal cortex (vmPFC) responsiveness during emotional processing have been reported in studies examining individual anxiety disorders. Studies are needed, however, which directly compare activation of amygdalo-cortical circuitry across multiple anxiety disorders within the same study. Here we compared cortico-limbic neurocircuitry across three different anxiety disorders using a well-validated emotional probe task.

METHODS

Sixty-five adult volunteers, including 22 healthy controls (HC) and participants meeting DSM-IV criteria for either posttraumatic stress disorder (14 PTSD), panic disorder (14 PD), or specific animal phobia (15 SP), underwent functional magnetic resonance imaging (fMRI) at 3 T while passively viewing backward-masked images of faces expressing fear, happy, and neutral emotions.

RESULTS

A group comprising all three anxiety disorders showed greater activation within the left amygdala and reduced activation within the vmPFC compared to the HC group during the masked fear versus neutral condition. Pairwise group comparisons showed that amygdala activation only reached significance for the PTSD versus HCs, whereas decreased vmPFC was only evident for SP and PD groups versus the HC group. Furthermore, activation did not differ among the anxiety groups when contrasted directly with one another. A similar pattern was observed for masked happy versus neutral faces.

CONCLUSIONS

Exclusive of specific diagnostic category, anxiety disorders were generally associated with increased activation of the amygdala and reduced activation within vmPFC. Categorical distinctions were generally weak or not observed and suggest that functional differences may reflect the magnitude of responses within a common neurocircuitry across disorders rather than activation of distinct systems.

Early life stress is associated with greater default network deactivation during working memory in healthy controls: a preliminary report

Early life stress (ELS) is a common risk factor for psychopathology, but there are few functional neuroimaging studies investigating its effects. In this preliminary study, we investigated the correlates of ELS exposure on the default network (DN) through measurements of task-associated DN deactivation. Data were analyzed from 19 subjects without psychiatric illness (10 with ELS). Subjects performed the working memory (WM) N-back task (including a 2-back WM and 0-back control condition) while undergoing functional MRI. We compared brain responses in the two groups across 5 bilateral DN regions using an a priori region of interest (ROI) analysis. The ELS group demonstrated significantly greater DN deactivation, observed in the right posterior cingulate cortex PCC, bilateral medial prefrontal cortex, left middle/superior frontal gyrus and right middle temporal region. These preliminary results indicate subjects with ELS demonstrate greater DN deactivations to WM challenges compared to non-ELS controls, potentially reflecting a biomarker of long-term effects of ELS exposure.

Avoidant symptoms in PTSD predict fear circuit activation during multimodal fear extinction

Convergent evidence suggests that individuals with posttraumatic stress disorder (PTSD) exhibit exaggerated avoidance behaviors as well as abnormalities in Pavlonian fear conditioning. However, the link between the two features of this disorder is not well understood. In order to probe the brain basis of aberrant extinction learning in PTSD, we administered a multimodal classical fear conditioning/extinction paradigm that incorporated affectively relevant information from two sensory channels (visual and tactile) while participants underwent fMRI scanning. The sample consisted of fifteen OEF/OIF veterans with PTSD. In response to conditioned cues and contextual information, greater avoidance symptomatology was associated with greater activation in amygdala, hippocampus, vmPFC, dmPFC, and insula, during both fear acquisition and fear extinction. Heightened responses to previously conditioned stimuli in individuals with more severe PTSD could indicate a deficiency in safety learning, consistent with PTSD symptomatology. The close link between avoidance symptoms and fear circuit activation suggests that this symptom cluster may be a key component of fear extinction deficits in PTSD and/or may be particularly amenable to change through extinction-based therapies.

Contextual exploration previous to an aversive event predicts long-term emotional consequences of severe stress

Traumatic stress can lead to long-term emotional alterations, which may result in Posttraumatic Stress Disorder (PTSD). Fear reactions triggered by conditioned cues and exacerbated emotional arousal in face of non-conditioned stimuli are among the most prominent features of PTSD. We hypothesized that long-term emotional alterations seen in PTSD may depend on the strength of context-trauma association. Here, we investigated the contribution of previous contextual exploration to the long-term emotional outcomes of an intense foot shock in rats. We exposed male Wistar rats to a highly stressful event (foot shock, 2 mA, 1 sec) allowing them to explore or not the chamber prior to trauma. We, then, evaluated the long-term effects on emotionality. Fear was assessed by the time spent in freezing behavior either upon re-exposure to trauma context or upon exposure to an unknown environment made potentially more aversive by presentation of an acoustic stimulus. Behaviors on the elevated-plus-maze and acoustic startle response were also assessed. The possibility to explore the environment immediately before the aversive event led to differential long-term emotional effects, including a heightened freezing response to re-exposure to context, blunted exploratory behavior, fear sensitization and exacerbation of the acoustic startle response, in contrast to the minor outcomes of the foot shock with no prior context exploration. The data showed the strong contribution of contextual learning to long-term behavioral effects of traumatic stress. We argue that contextual representation contributes to the robust long-term behavioral alterations seen in this model of traumatic stress.

Disrupted amygdala-prefrontal functional connectivity in civilian women with posttraumatic stress disorder

Many features of posttraumatic stress disorder (PTSD) can be linked to exaggerated and dysregulated emotional responses. Central to the neurocircuitry regulating emotion are functional interactions between the amygdala and the ventromedial prefrontal cortex (vmPFC). Findings from human and animal studies suggest that disruption of this circuit predicts individual differences in emotion regulation. However, only a few studies have examined amygdala-vmPFC connectivity in the context of emotional processing in PTSD. The aim of the present research was to investigate the hypothesis that PTSD is associated with disrupted functional connectivity of the amygdala and vmPFC in response to emotional stimuli, extending previous findings by demonstrating such links in an understudied, highly traumatized, civilian population. 40 African-American women with civilian trauma (20 with PTSD and 20 non-PTSD controls) were recruited from a large urban hospital. Participants viewed fearful and neutral face stimuli during functional magnetic resonance imaging (fMRI). Relative to controls, participants with PTSD showed an increased right amygdala response to fearful stimuli (p(corr) < .05). Right amygdala activation correlated positively with the severity of hyperarousal symptoms in the PTSD group. Participants with PTSD showed decreased functional connectivity between the right amygdala and left vmPFC (p(corr) < .05). The findings are consistent with previous findings showing PTSD is associated with an exaggerated response of amygdala-mediated emotional arousal systems. This is the first study to show that the amygdala response may be accompanied by disruption of an amygdala-vmPFC functional circuit that is hypothesized to be involved in prefrontal cortical regulation of amygdala responsivity.

Cannabinoid modulation of prefrontal-limbic activation during fear extinction learning and recall in humans

Pre-extinction administration of Δ9-tetrahydrocannibinol (THC) facilitates recall of extinction in healthy humans, and evidence from animal studies suggest that this likely occurs via enhancement of the cannabinoid system within the ventromedial prefrontal cortex (vmPFC) and hippocampus (HIPP), brain structures critical to fear extinction. However, the effect of cannabinoids on the underlying neural circuitry of extinction memory recall in humans has not been demonstrated. We conducted a functional magnetic resonance imaging (fMRI) study using a randomized, double-blind, placebo-controlled, between-subjects design (N=14/group) coupled with a standard Pavlovian fear extinction paradigm and an acute pharmacological challenge with oral dronabinol (synthetic THC) in healthy adult volunteers. We examined the effects of THC on vmPFC and HIPP activation when tested for recall of extinction learning 24 h after extinction learning. Compared to subjects who received placebo, participants who received THC showed increased vmPFC and HIPP activation to a previously extinguished conditioned stimulus (CS+E) during extinction memory recall. This study provides the first evidence that pre-extinction administration of THC modulates prefrontal-limbic circuits during fear extinction in humans and prompts future investigation to test if cannabinoid agonists can rescue or correct the impaired behavioral and neural function during extinction recall in patients with PTSD. Ultimately, the cannabinoid system may serve as a promising target for innovative intervention strategies (e.g. pharmacological enhancement of exposure-based therapy) in PTSD and other fear learning-related disorders.

Uncertainty and anticipation in anxiety: an integrated neurobiological and psychological perspective

Uncertainty about a possible future threat disrupts our ability to avoid it or to mitigate its negative impact and thus results in anxiety. Here, we focus the broad literature on the neurobiology of anxiety through the lens of uncertainty. We identify five processes that are essential for adaptive anticipatory responses to future threat uncertainty and propose that alterations in the neural instantiation of these processes result in maladaptive responses to uncertainty in pathological anxiety. This framework has the potential to advance the classification, diagnosis and treatment of clinical anxiety.

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.

Childhood and adult trauma both correlate with dorsal anterior cingulate activation to threat in combat veterans

BACKGROUND

Prior studies of adult post-traumatic stress disorder (PTSD) suggest abnormal functioning of prefrontal and limbic regions. Cumulative childhood and adult trauma exposures are major risk factors for developing adult PTSD, yet their contribution to neural dysfunction in PTSD remains poorly understood. This study aimed to examine the neural correlates of childhood and adult trauma exposure and post-traumatic stress symptoms (PTSS) within a single model. Method Medication-free male combat veterans (n = 28, average age 26.6 years) with a wide range of PTSS were recruited from the community between 2010 and 2011. Subjects completed an emotional face-morphing task while undergoing functional magnetic resonance imaging (fMRI). Clinical ratings included the Clinician-Administered PTSD Scale (CAPS), Childhood Trauma Questionnaire (CTQ) and Combat Exposure Scale (CES). A priori regions were examined through multivariate voxelwise regression in SPM8, using depressive symptoms and IQ as covariates.

RESULTS

In the angry condition, CAPS scores correlated positively with activation in the medial prefrontal cortex [mPFC; Brodmann area (BA) 10, z = 3.51], hippocampus (z = 3.47), insula (z = 3.62) and, in earlier blocks, the amygdala. CES and CTQ correlated positively with activation in adjacent areas of the dorsal anterior cingulate cortex (dACC; BA 32, z = 3.70 and BA 24, z = 3.88 respectively). In the happy condition, CAPS, CTQ and CES were not correlated significantly with activation patterns.

CONCLUSIONS

dACC activation observed in prior studies of PTSD may be attributable to the cumulative effects of childhood and adult trauma exposure. By contrast, insula, hippocampus and amygdala activation may be specific to PTSS. The specificity of these results to threat stimuli, but not to positive stimuli, is consistent with abnormalities in threat processing associated with PTSS.

The contextual brain: implications for fear conditioning, extinction and psychopathology

Contexts surround and imbue meaning to events; they are essential for recollecting the past, interpreting the present and anticipating the future. Indeed, the brain's capacity to contextualize information permits enormous cognitive and behavioural flexibility. Studies of Pavlovian fear conditioning and extinction in rodents and humans suggest that a neural circuit including the hippocampus, amygdala and medial prefrontal cortex is involved in the learning and memory processes that enable context-dependent behaviour. Dysfunction in this network may be involved in several forms of psychopathology, including post-traumatic stress disorder, schizophrenia and substance abuse disorders.

Neural, psychophysiological, and behavioral markers of fear processing in PTSD: a review of the literature

As presently defined, post-traumatic stress disorder (PTSD) is an amalgam of symptoms falling into: re-experiencing of the trauma, avoidance of reminders of it, emotional numbing and hyperarousal. PTSD has a well-known proximate cause, commonly occurring after a life-threatening event that induces a response of intense fear, horror, and helplessness. Much of the advancement in understanding of the neurobiology of PTSD has emerged from conceptualizing the disorder as one that involves substantial dysfunction in fear processing. This article reviews recent knowledge of fear processing markers in PTSD. A systematic search was performed of reports within the specific three-year publication time period of January 2010 to December 2012. We identified a total of 31 studies reporting fear processing markers in PTSD. We further categorized them according to the following classification: (1) neural-activation markers (n=10), (2) psychophysiological markers (n=14), and (3) behavioral markers (n=7). Across most studies reviewed here, significant differences between individuals with PTSD and healthy controls were shown. Methodological, theoretical and clinical implications were discussed.

Current status on behavioral and biological markers of PTSD: a search for clarity in a conflicting literature

Extensive research has identified stereotypic behavioral and biological abnormalities in post-traumatic stress disorder (PTSD), such as heightened autonomic activity, an exaggerated startle response, reduced basal cortisol levels and cognitive impairments. We have reviewed primary research in this area, noting that factors involved in the susceptibility and expression of PTSD symptoms are more complex and heterogeneous than is commonly stated, with extensive findings which are inconsistent with the stereotypic behavioral and biological profile of the PTSD patient. A thorough assessment of the literature indicates that interactions among myriad susceptibility factors, including social support, early life stress, sex, age, peri- and post-traumatic dissociation, cognitive appraisal of trauma, neuroendocrine abnormalities and gene polymorphisms, in conjunction with the inconsistent expression of the disorder across studies, confounds attempts to characterize PTSD as a monolithic disorder. Overall, our assessment of the literature addresses the great challenge in developing a behavioral and biomarker-based diagnosis of PTSD.

Neural functional and structural correlates of childhood maltreatment in women with intimate-partner violence-related posttraumatic stress disorder

Childhood maltreatment (CM) is a strong risk factor for development of posttraumatic stress disorder (PTSD) upon adult exposure to extreme adverse events. However, the neural underpinnings of this relationship are not well understood. Here, we test the hypothesis that severity of CM history is positively correlated with emotion-processing limbic and prefrontal brain activation/connectivity and negatively correlated with prefrontal gray matter volumes in women with PTSD due to intimate-partner violence (IPV-PTSD). Thirty-three women with IPV-PTSD underwent structural and functional magnetic resonance imaging while completing a facial emotion processing task. Multivariate regressions examined the relationship of CM to patterns of activation, connectivity, and gray matter volumes. CM severity was: (a) positively correlated with ventral ACC activation while processing angry faces; (b) negatively correlated with dorsal ACC and insula activation while processing fear and angry faces, arising from positive correlations with the shape-matching baseline; (c) positively correlated with limbic-prefrontal connectivity while processing fear faces but negatively correlated with amygdalo-insular connectivity while processing fear and angry; and (d) negatively correlated with prefrontal gray matter volumes. These results suggest CM exposure may account for variability in limbic/prefrontal brain function and prefrontal structure in adulthood PTSD and offer one potential mechanism through which CM confers risk to future development of PTSD.

The Role of BDNF-TrkB Signaling in the Pathogenesis of PTSD

Posttraumatic Stress Disorder (PTSD) is a prevalent, chronic, and disabling anxiety disorder that may develop following exposure to a traumatic event. The majority of individuals with PTSD often have comorbid psychiatric conditions such as major depression, generalized anxiety disorder, and substance use disorders, and are at increased risk for suicide. Despite the public health significance of PTSD, relatively little is known about the etiology or pathophysiology of this disorder, and pharmacotherapy development to date has been largely opportunistic instead of mechanism-based. One promising target for modulation is Tropomyosin Receptor Kinase B (TrkB), the receptor for Brain-Derived Neurotrophic Factor (BDNF), a signaling pathway important for neuronal plasticity, survival, and growth. The following discusses how genetic and environmental alterations to this signaling pathway may contribute to anatomical and functional changes in the hippocampus, amygdala, anterior cingulate cortex, ventromedial prefrontal cortex, and the nucleus accumbens. Changes in these brain regions may in turn contribute to the predisposition to or maintenance of some of the clinical manifestations of PTSD, including intrusive memories, hyperarousal, increased fear, and emotional numbing.

Decreased default network connectivity is associated with early life stress in medication-free healthy adults

Early life stress (ELS) is a significant risk factor for psychopathology, although there are few functional imaging studies investigating its effects. Previous literature suggests that ELS is associated with changes in structure and function in the medial prefrontal cortex (MPFC), which forms the main anterior node of the default network (DN). This study investigated the impact of ELS history on resting state DN connectivity, using seed-based correlation analyses (SCA) involving the posterior cingulate cortex (PCC). Data were analyzed from 22 adult subjects without psychiatric or medical illness (13 with and 9 without ELS); none were taking psychotropic medication. Relative to controls, the ELS group had significant decreases in DN connectivity, observed between the PCC seed and the MPFC and inferior temporal cortex. Further analyses revealed a trend-level increase in connectivity between the amygdala and MPFC associated with ELS history. In conclusion, this study found that subjects with ELS, in the absence of psychiatric illness and medication exposure, demonstrated decreased DN connectivity, and trend-level increases in connectivity between the amygdala and MPFC. These findings suggest that altered resting state connectivity is a correlate of stress exposure, rather than a product of medication or psychiatric morbidity.

Biological studies of post-traumatic stress disorder

Post-traumatic stress disorder (PTSD) is the only major mental disorder for which a cause is considered to be known: that is, an event that involves threat to the physical integrity of oneself or others and induces a response of intense fear, helplessness or horror. Although PTSD is still largely regarded as a psychological phenomenon, over the past three decades the growth of the biological PTSD literature has been explosive, and thousands of references now exist. Ultimately, the impact of an environmental event, such as a psychological trauma, must be understood at organic, cellular and molecular levels. This Review attempts to present the current state of this understanding on the basis of psychophysiological, structural and functional neuroimaging, and endocrinological, genetic and molecular biological studies in humans and in animal models.

Neural systems for cognitive and emotional processing in posttraumatic stress disorder

Individuals with posttraumatic stress disorder (PTSD) show altered cognition when trauma-related material is present. PTSD may lead to enhanced processing of trauma-related material, or it may cause impaired processing of trauma-unrelated information. However, other forms of emotional information may also alter cognition in PTSD. In this review, we discuss the behavioral and neural effects of emotion processing on cognition in PTSD, with a focus on neuroimaging results. We propose a model of emotion-cognition interaction based on evidence of two network models of altered brain activation in PTSD. The first is a trauma-disrupted network made up of ventrolateral PFC, dorsal anterior cingulate cortex (ACC), hippocampus, insula, and dorsomedial PFC that are differentially modulated by trauma content relative to emotional trauma-unrelated information. The trauma-disrupted network forms a subnetwork of regions within a larger, widely recognized network organized into ventral and dorsal streams for processing emotional and cognitive information that converge in the medial PFC and cingulate cortex. Models of fear learning, while not a cognitive process in the conventional sense, provide important insights into the maintenance of the core symptom clusters of PTSD such as re-experiencing and hypervigilance. Fear processing takes place within the limbic corticostriatal loop composed of threat-alerting and threat-assessing components. Understanding the disruptions in these two networks, and their effect on individuals with PTSD, will lead to an improved knowledge of the etiopathogenesis of PTSD and potential targets for both psychotherapeutic and pharmacotherapeutic interventions.

Emotion and cognition interactions in PTSD: a review of neurocognitive and neuroimaging studies

Posttraumatic stress disorder (PTSD) is a psychiatric syndrome that develops after exposure to terrifying and life-threatening events including warfare, motor-vehicle accidents, and physical and sexual assault. The emotional experience of psychological trauma can have long-term cognitive effects. The hallmark symptoms of PTSD involve alterations to cognitive processes such as memory, attention, planning, and problem solving, underscoring the detrimental impact that negative emotionality has on cognitive functioning. As such, an important challenge for PTSD researchers and treatment providers is to understand the dynamic interplay between emotion and cognition. Contemporary cognitive models of PTSD theorize that a preponderance of information processing resources are allocated toward threat detection and interpretation of innocuous stimuli as threatening, narrowing one's attentional focus at the expense of other cognitive operations. Decades of research have shown support for these cognitive models of PTSD using a variety of tasks and methodological approaches. The primary goal of this review is to summarize the latest neurocognitive and neuroimaging research of emotion-cognition interactions in PTSD. To directly assess the influence of emotion on cognition and vice versa, the studies reviewed employed challenge tasks that included both cognitive and emotional components. The findings provide evidence for memory and attention deficits in PTSD that are often associated with changes in functional brain activity. The results are reviewed to provide future directions for research that may direct better and more effective treatments for PTSD.

A phenotype of early infancy predicts reactivity of the amygdala in male adults

One of the central questions that has occupied those disciplines concerned with human development is the nature of continuities and discontinuities from birth to maturity. The amygdala has a central role in the processing of novelty and emotion in the brain. Although there is considerable variability among individuals in the reactivity of the amygdala to novel and emotional stimuli, the origin of these individual differences is not well understood. Four-month old infants called high reactive (HR) demonstrate a distinctive pattern of vigorous motor activity and crying to specific unfamiliar visual, auditory and olfactory stimuli in the laboratory. Low-reactive infants show the complementary pattern. Here, we demonstrate that the HR infant phenotype predicts greater amygdalar reactivity to novel faces almost two decades later in adults. A prediction of individual differences in brain function at maturity can be made on the basis of a single behavioral assessment made in the laboratory at 4 months of age. This is the earliest known human behavioral phenotype that predicts individual differences in patterns of neural activity at maturity. These temperamental differences rooted in infancy may be relevant to understanding individual differences in vulnerability and resilience to clinical psychiatric disorder. Males who were HR infants showed particularly high levels of reactivity to novel faces in the amygdala that distinguished them as adults from all other sex/temperament subgroups, suggesting that their amygdala is particularly prone to engagement by unfamiliar faces. These findings underline the importance of taking gender into account when studying the developmental neurobiology of human temperament and anxiety disorders. The genetic study of behavioral and biologic intermediate phenotypes (or 'endophenotypes') indexing anxiety-proneness offers an important alternative to examining phenotypes based on clinically defined disorder. As the HR phenotype is characterized by specific patterns of reactivity to elemental visual, olfactory and auditory stimuli, well before complex social behaviors such as shyness or fearful interaction with strangers can be observed, it may be closer to underlying neurobiological mechanisms than behavioral profiles observed later in life. This possibility, together with the fact that environmental factors have less time to impact the 4-month phenotype, suggests that this temperamental profile may be a fruitful target for high-risk genetic studies.

Post-traumatic stress symptoms correlate with smaller subgenual cingulate, caudate, and insula volumes in unmedicated combat veterans

Prior studies have examined differences in brain volume between patients with post-traumatic stress disorder (PTSD) and control subjects. Convergent findings include smaller hippocampus and medial prefrontal cortex volumes in PTSD. However, post-traumatic stress symptoms (PTSS) exist on a spectrum, and neural changes may occur beyond the diagnostic threshold of PTSD. We examined the relationship between PTSS and gray matter among combat-exposed U.S. military veterans. Structural brain magnetic resonance imaging (MRI) was obtained on 28 combat veterans from Operations Enduring and Iraqi Freedom. PTSS were assessed using the Clinician-Administered PTSD Scale (CAPS). Thirteen subjects met criteria for PTSD. Subjects were unmedicated, and free of major comorbid psychiatric disorders. Images were analyzed using voxel-based morphometry, and regressed against the total CAPS score and trauma load. Images were subsequently analyzed by diagnosis of PTSD vs. non-PTSD. CAPS scores were inversely correlated with volumes of the subgenual cingulate (sgACC), caudate, hypothalamus, insula, and left middle temporal gyrus (MTG). Group contrast revealed smaller sgACC, caudate, hypothalamus, left insula, left MTG, and right MFG in the PTSD group. PTSS are associated with abnormalities in limbic structures that may underlie the pathophysiology of PTSD. These abnormalities exist on a continuum with PTSS, beyond a diagnosis of PTSD.

Brain activation to facial expressions in youth with PTSD symptoms

OBJECTIVE

This study examined activation to facial expressions in youth with a history of interpersonal trauma and current posttraumatic stress symptoms (PTSS) compared to healthy controls (HC).

DESIGN AND ANALYSIS

Twenty-three medication-naive youth with PTSS and 23 age- and gender-matched HC underwent functional magnetic resonance imaging (fMRI) while viewing fearful, angry, sad, happy, and neutral faces. Data were analyzed for group differences in location of activation, as well as timing of activation during the early versus late phase of the block. Using SPM5, significant activation (P < .05 FWE [Family-Wise Error] corrected, extent = 10 voxels) associated with the main effect of group was identified. Activation from selected clusters was extracted to SPSS software for further analysis of specific facial expressions and temporal patterns of activation.

RESULTS

The PTSS group showed significantly greater activation than controls in several regions, including the amygdala/hippocampus, medial prefrontal cortex, insula, and ventrolateral prefrontal cortex, and less activation than controls in the dorsolateral prefrontal cortex (DLPFC). These group differences in activation were greatest during angry, happy, and neutral faces, and predominantly during the early phase of the block. Post hoc analyses showed significant Group × Phase interactions in the right amygdala and left hippocampus.

CONCLUSIONS

Traumatic stress may impact development of brain regions important for emotion processing. Timing of activation may be altered in youth with PTSS.

Sex differences in the neurobiology of fear conditioning and extinction: a preliminary fMRI study of shared sex differences with stress-arousal circuitry

BACKGROUND

The amygdala, hippocampus, medial prefrontal cortex (mPFC) and brain-stem subregions are implicated in fear conditioning and extinction, and are brain regions known to be sexually dimorphic. We used functional magnetic resonance imaging (fMRI) to investigate sex differences in brain activity in these regions during fear conditioning and extinction.

METHODS

Subjects were 12 healthy men comparable to 12 healthy women who underwent a 2-day experiment in a 3 T MR scanner. Fear conditioning and extinction learning occurred on day 1 and extinction recall occurred on day 2. The conditioned stimuli were visual cues and the unconditioned stimulus was a mild electric shock. Skin conductance responses (SCR) were recorded throughout the experiment as an index of the conditioned response. fMRI data (blood-oxygen-level-dependent [BOLD] signal changes) were analyzed using SPM8.

RESULTS

Findings showed no significant sex differences in SCR during any experimental phases. However, during fear conditioning, there were significantly greater BOLD-signal changes in the right amygdala, right rostral anterior cingulate (rACC) and dorsal anterior cingulate cortex (dACC) in women compared with men. In contrast, men showed significantly greater signal changes in bilateral rACC during extinction recall.

CONCLUSIONS

These results indicate sex differences in brain activation within the fear circuitry of healthy subjects despite similar peripheral autonomic responses. Furthermore, we found that regions where sex differences were previously reported in response to stress, also exhibited sex differences during fear conditioning and extinction.

Sex differences in the neurobiology of fear conditioning and extinction: a preliminary fMRI study of shared sex differences with stress-arousal circuitry

BACKGROUND

The amygdala, hippocampus, medial prefrontal cortex (mPFC) and brain-stem subregions are implicated in fear conditioning and extinction, and are brain regions known to be sexually dimorphic. We used functional magnetic resonance imaging (fMRI) to investigate sex differences in brain activity in these regions during fear conditioning and extinction.

METHODS

Subjects were 12 healthy men comparable to 12 healthy women who underwent a 2-day experiment in a 3 T MR scanner. Fear conditioning and extinction learning occurred on day 1 and extinction recall occurred on day 2. The conditioned stimuli were visual cues and the unconditioned stimulus was a mild electric shock. Skin conductance responses (SCR) were recorded throughout the experiment as an index of the conditioned response. fMRI data (blood-oxygen-level-dependent [BOLD] signal changes) were analyzed using SPM8.

RESULTS

Findings showed no significant sex differences in SCR during any experimental phases. However, during fear conditioning, there were significantly greater BOLD-signal changes in the right amygdala, right rostral anterior cingulate (rACC) and dorsal anterior cingulate cortex (dACC) in women compared with men. In contrast, men showed significantly greater signal changes in bilateral rACC during extinction recall.

CONCLUSIONS

These results indicate sex differences in brain activation within the fear circuitry of healthy subjects despite similar peripheral autonomic responses. Furthermore, we found that regions where sex differences were previously reported in response to stress, also exhibited sex differences during fear conditioning and extinction.

Fear extinction as a model for translational neuroscience: ten years of progress

The psychology of extinction has been studied for decades. Approximately 10 years ago, however, there began a concerted effort to understand the neural circuits of extinction of fear conditioning, in both animals and humans. Progress during this period has been facilitated by a high degree of coordination between rodent and human researchers examining fear extinction. Here we review the major advances and highlight new approaches to understanding and exploiting fear extinction. Research in fear extinction could serve as a model for translational research in other areas of behavioral neuroscience.

Resting amygdala and medial prefrontal metabolism predicts functional activation of the fear extinction circuit

OBJECTIVE

Individual differences in a person's ability to control fear have been linked to activation in the dorsal anterior cingulate cortex, the ventromedial prefrontal cortex, and the amygdala. This study investigated whether functional variance in this network can be predicted by resting metabolism in these same regions.

METHOD

The authors measured resting brain metabolism in healthy volunteers with positron emission tomography using [18F]fluorodeoxyglucose. This was followed by a 2-day fear conditioning and extinction training paradigm using functional MRI to measure brain activation during fear extinction and recall. The authors used skin conductance response to index conditioned responding, and they used resting metabolism in the amygdala, the dorsal anterior cingulate cortex, and the ventromedial prefrontal cortex to predict responses during fear extinction and extinction recall.

RESULTS

During extinction training, resting amygdala metabolism positively predicted activation in the ventromedial prefrontal cortex and negatively predicted activation in the dorsal anterior cingulate cortex. In contrast, during extinction recall, resting amygdala metabolism negatively predicted activation in the ventromedial prefrontal cortex and positively predicted activation in the dorsal anterior cingulate cortex. In addition, resting metabolism in the dorsal anterior cingulate cortex predicted fear expression (as measured by skin conductance response) during extinction recall.

CONCLUSIONS

Resting brain metabolism predicted neuronal reactivity and skin conductance changes associated with the recall of the fear extinction memory.

Sex differences, gonadal hormones and the fear extinction network: implications for anxiety disorders

Convergent data from rodents and human studies have led to the development of models describing the neural mechanisms of fear extinction. Key components of the now well-characterized fear extinction network include the amygdala, hippocampus, and medial prefrontal cortical regions. These models are fueling novel hypotheses that are currently being tested with much refined experimental tools to examine the interactions within this network. Lagging far behind, however, is the examination of sex differences in this network and how sex hormones influence the functional activity and reactivity of these brain regions in the context of fear inhibition. Indeed, there is a large body of literature suggesting that sex hormones, such as estrogen, do modulate neural plasticity within the fear extinction network, especially in the hippocampus.After a brief overview of the fear extinction network, we summarize what is currently known about sex differences in fear extinction and the influence of gonadal hormones on the fear extinction network. We then go on to propose possible mechanisms by which sex hormones, such as estrogen, may influence neural plasticity within the fear extinction network. We end with a discussion of how knowledge to be gained from developing this line of research may have significant ramifications towards the etiology, epidemiology and treatment of anxiety disorders.

Single prolonged stress disrupts retention of extinguished fear in rats

Clinical research has linked post-traumatic stress disorder (PTSD) with deficits in fear extinction. However, it is not clear whether these deficits result from stress-related changes in the acquisition or retention of extinction or in the regulation of extinction memories by context, for example. In this study, we used the single prolonged stress (SPS) animal model of PTSD and fear conditioning procedures to examine the effects of prior traumatic stress on the acquisition, retention, and context-specificity of extinction. SPS administered one week prior to fear conditioning had no effect on the acquisition of fear conditioning or extinction but disrupted the retention of extinction memories for both contextual and cued fear. This SPS effect required a post-stress incubation period to manifest. The results demonstrate that SPS disrupts extinction retention, leading to enhanced fear renewal; further research is needed to identify the neurobiological processes through which SPS induces these effects.

Emotion and cognition interactions in PTSD: a review of neurocognitive and neuroimaging studies

Posttraumatic stress disorder (PTSD) is a psychiatric syndrome that develops after exposure to terrifying and life-threatening events including warfare, motor-vehicle accidents, and physical and sexual assault. The emotional experience of psychological trauma can have long-term cognitive effects. The hallmark symptoms of PTSD involve alterations to cognitive processes such as memory, attention, planning, and problem solving, underscoring the detrimental impact that negative emotionality has on cognitive functioning. As such, an important challenge for PTSD researchers and treatment providers is to understand the dynamic interplay between emotion and cognition. Contemporary cognitive models of PTSD theorize that a preponderance of information processing resources are allocated toward threat detection and interpretation of innocuous stimuli as threatening, narrowing one's attentional focus at the expense of other cognitive operations. Decades of research have shown support for these cognitive models of PTSD using a variety of tasks and methodological approaches. The primary goal of this review is to summarize the latest neurocognitive and neuroimaging research of emotion-cognition interactions in PTSD. To directly assess the influence of emotion on cognition and vice versa, the studies reviewed employed challenge tasks that included both cognitive and emotional components. The findings provide evidence for memory and attention deficits in PTSD that are often associated with changes in functional brain activity. The results are reviewed to provide future directions for research that may direct better and more effective treatments for PTSD.

The study of fear extinction: implications for anxiety disorders

In this review, the authors propose that the fear extinction model can be used as an experimental tool to cut across symptom dimensions of multiple anxiety disorders to enhance our understanding of the psychopathology of these disorders and potentially facilitate the detection of biomarkers for them. The authors evaluate evidence for this proposition from studies examining the neurocircuitry underlying fear extinction in rodents, healthy humans, and clinical populations. The authors also assess the potential use of the fear extinction model to predict vulnerability for anxiety and treatment response and to improve existing treatments or develop novel ones. Finally, the authors suggest potential directions for future research that will help to further validate extinction as a biomarker for anxiety across diagnostic categories and to bridge the gap between basic neuroscience and clinical practice.

An fMRI study of unconditioned responses in post-traumatic stress disorder

BACKGROUND

Both fear and pain processing are altered in post-traumatic stress disorder (PTSD), as evidenced by functional neuroimaging studies showing increased amygdala responses to threats, and increased insula, putamen and caudate activity in response to heat pain. Using psychophysiology and functional magnetic resonance imaging, we studied conditioned and unconditioned autonomic and neuronal responses in subjects with PTSD versus trauma-exposed non-PTSD control (TENC) subjects. A design using an electric shock selected by subjects to be 'highly annoying but not painful' as an unconditioned stimulus (US) with partially reinforced cues allowed us to partly disentangle the expectancy- and prediction-error components from sensory components of the unconditioned response.

RESULTS

Whereas responses to the conditioned stimulus (CS) were similar in PTSD and TENC, the former displayed higher putamen, insula, caudate and amygdala responses to the US. Reactivity to the US in the anterior insula correlated with PTSD symptom severity. Functional connectivity analyses using the putamen as a seed region indicated that TENC subjects had increased amygdala-putamen connectivity during US delivery; this connection was disengaged in PTSD.

CONCLUSIONS

Our results indicate that although neural processing of fear learning in people with PTSD seems to be comparable with controls, neural responses to unconditioned aversive stimuli in PTSD seem to be increased.