Panic disorder: a product of classical conditioning

Reduction of Aversive Learning Rates in Pavlovian Conditioning by Angiotensin II Antagonist Losartan: A Randomized Controlled Trial

BACKGROUND

Angiotensin receptor blockade has been linked to aspects of aversive learning and memory formation and to the prevention of posttraumatic stress disorder symptom development.

METHODS

We investigated the influence of the angiotensin receptor blocker losartan on aversive Pavlovian conditioning using a probabilistic learning paradigm. In a double-blind, randomized, placebo-controlled design, we tested 45 (18 female) healthy volunteers during a baseline session, after application of losartan or placebo (drug session), and during a follow-up session. During each session, participants engaged in a task in which they had to predict the probability of an electrical stimulation on every trial while the true shock contingencies switched repeatedly between phases of high and low shock threat. Computational reinforcement learning models were used to investigate learning dynamics.

RESULTS

Acute administration of losartan significantly reduced participants' adjustment during both low-to-high and high-to-low threat changes. This was driven by reduced aversive learning rates in the losartan group during the drug session compared with baseline. The 50-mg drug dose did not induce reduction of blood pressure or change in reaction times, ruling out a general reduction in attention and engagement. Decreased adjustment of aversive expectations was maintained at a follow-up session 24 hours later.

CONCLUSIONS

This study shows that losartan acutely reduces Pavlovian learning in aversive environments, thereby highlighting a potential role of the renin-angiotensin system in anxiety development.

Conditional effects of state fear of negative evaluation on restrictive eating behaviors

Fear of being evaluated negatively by others is a risk factor for the development of disordered eating. Specifically, trait level fear of negative evaluation (FNE) predicts disordered eating severity above other social anxiety traits. However, it remains unclear how state levels of this fear may impact eating behavior. The current study aimed to examine this risk factor in the context of state-level eating behavior. We hypothesized that: (a) elevated levels of state FNE would enhance the relationship between restraint and restriction and (b) we sought to explore the predictive nature of high trait FNE on restriction. Study procedures for N = 64 undergraduate students included assessment of dietary restraint, fear of negative evaluation, and hypothetical meal choice in the context of several proposed social and non-social settings. Results indicated that higher state FNE was related to more restrictive food choice across settings, and levels of trait FNE were not related to food choices. State FNE did not enhance the relationship between restraint and restriction. This project sought to examine the degree to which fear of negative evaluation impacts the relationship between dietary restraint and restriction, testing a unique risk factor for the development of eating psychopathology.

Neuropeptide S precursor knockout mice display memory and arousal deficits

Activation of neuropeptide S (NPS) signaling has been found to produce arousal, wakefulness, anxiolytic-like behaviors, and enhanced memory formation. In order to further study physiological functions of the NPS system, we generated NPS precursor knockout mice by homologous recombination in embryonic stem cells. NPS^-/- mice were viable, fertile, and anatomically normal, when compared to their wild-type and heterozygous littermates. The total number of NPS neurons-although no longer synthesizing the peptide - was not affected by the knockout, as analyzed in NPS^-/- /NPS^EGFP double transgenic mice. Analysis of behavioral phenotypes revealed significant deficits in exploratory activity in NPS^-/- mice. NPS precursor knockout mice displayed attenuated arousal in the hole board test, visible as reduced total nose pokes and number of holes inspected, that was not confounded by increased repetitive or stereotypic behavior. Importantly, long-term memory was significantly impaired in NPS^-/- mice in the inhibitory avoidance paradigm. NPS precursor knockout mice displayed mildly increased anxiety-like behaviors in three different tests measuring responses to stress and novelty. Interestingly, heterozygous littermates often presented behavioral deficits similar to NPS^-/- mice or displayed intermediate phenotype. These observations may suggest limited ligand availability in critical neural circuits. Overall, phenotypical changes in NPS^-/- mice are similar to those observed in NPS receptor knockout mice and support earlier findings that suggest major functions of the NPS system in arousal, regulation of anxiety and stress, and memory formation.

Human fear acquisition deficits in relation to genetic variants of the corticotropin-releasing hormone receptor 1 and the serotonin transporter--revisited

We recently showed that a genetic polymorphism (rs878886) in the human corticotropin-releasing hormone receptor 1 (CRHR1) is associated with reduced fear-conditioned responses to a threat cue. This is a potentially important finding considering that the failure to acquire fear contingencies can leave an individual in a maladaptive state of more generalized anxiety. Consistent with that idea, the CRHR1-dependent fear acquisition deficit translated into heightened contextual anxiety when taking genetic variability within the serotonin transporter long polymorphic region (5-HTTLPR) into account. To replicate our previous findings, we conducted a replication study in 224 healthy medication-free human subjects using the exact same cue and context virtual reality fear-conditioning procedure as in study by Heitland et al. (2013). In the replication study, consistent with the original findings, CRHR1 rs878886 G-allele carriers showed reduced acquisition of cue-specific fear-conditioned responses compared with C/C homozygotes. Also, in this larger sample the cue acquisition deficit of G-allele carriers translated into heightened contextual anxiety, even independent of 5-HTT gene variation. In contrast to our earlier findings, there was an additional interaction effect of CRHR1 rs878886 and the triallelic 5-HTTLPR/rs25531 variant on cued fear acquisition. In summary, this study replicated the initially reported association of the CRHR1 rs878886 G-allele with cued fear acquisition deficits, albeit with a different pattern of results regarding the interaction with 5-HTT variation. This further supports the notion that the human corticotropin-releasing hormone plays a role in the acquisition of fears.

Nicotine modulation of fear memories and anxiety: Implications for learning and anxiety disorders

Anxiety disorders are a group of crippling mental diseases affecting millions of Americans with a 30% lifetime prevalence and costs associated with healthcare of $42.3 billion. While anxiety disorders show high levels of co-morbidity with smoking (45.3% vs. 22.5% in healthy individuals), they are also more common among the smoking population (22% vs. 11.1% in the non-smoking population). Moreover, there is clear evidence that smoking modulates symptom severity in patients with anxiety disorders. In order to better understand this relationship, several animal paradigms are used to model several key symptoms of anxiety disorders; these include fear conditioning and measures of anxiety. Studies clearly demonstrate that nicotine mediates acquisition and extinction of fear as well as anxiety through the modulation of specific subtypes of nicotinic acetylcholine receptors (nAChRs) in brain regions involved in emotion processing such as the hippocampus. However, the direction of nicotine's effects on these behaviors is determined by several factors that include the length of administration, hippocampus-dependency of the fear learning task, and source of anxiety (novelty-driven vs. social anxiety). Overall, the studies reviewed here suggest that nicotine alters behaviors related to fear and anxiety and that nicotine contributes to the development, maintenance, and reoccurrence of anxiety disorders.

Neural correlates of procedural variants in cognitive-behavioral therapy: a randomized, controlled multicenter FMRI study

BACKGROUND

Cognitive behavioral therapy (CBT) is an effective treatment for panic disorder with agoraphobia (PD/AG). It is unknown, how variants of CBT differentially modulate brain networks involved in PD/AG. This study was aimed to evaluate the effects of therapist-guided (T+) versus self-guided (T-) exposure on the neural correlates of fear conditioning in PD/AG.

METHOD

In a randomized, controlled multicenter clinical trial in medication-free patients with PD/AG who were treated with 12 sessions of manualized CBT, functional magnetic resonance imaging (fMRI) was used during fear conditioning before (t1) and after CBT (t2). Quality-controlled fMRI data from 42 patients and 42 healthy subjects (HS) were obtained. Patients were randomized to two variants of CBT (T+, n = 22, and T-, n = 20).

RESULTS

The interaction of diagnosis (PD/AG, HS), treatment group (T+, T-), time point (t1, t2) and stimulus type (conditioned stimulus: yes, no) revealed activation in the left hippocampus and the occipitotemporal cortex. The T+ group demonstrated increased activation of the hippocampus at t2 (t2 > t1), which was positively correlated with treatment outcome, and a decreased connectivity between the left inferior frontal gyrus and the left hippocampus across time (t1 > t2).

CONCLUSION

After T+ exposure, contingency-encoding processes related to the posterior hippocampus are augmented and more decoupled from processes of the left inferior frontal gyrus, previously shown to be dysfunctionally activated in PD/AG. Linking single procedural variants to neural substrates offers the potential to inform about the optimization of targeted psychotherapeutic interventions.

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 (GS) (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 GS. 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 GS 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 posttraumatic stress disorder (PTSD) where much of the traumatic exposure may involve sounds.

Cardiophobia: An Anxiety Disorder in Its Own Right?

Cardiophobic persons repeatedly present with complaints of chest pain and heart palpitations accompanied by fears of having a heart attack and of dying. They focus attention on their heart when experiencing stress and arousal, perceive its function in a phobic manner, and continue to believe they suffer from an organic heart problem despite repeated negative medical tests. To reduce anxiety, they seek continuous reassurance, make excessive use of medical facilities, and avoid activities believed to bring on symptoms. This article analyses the evidence for viewing cardiophobia as a phobic disorder in its own right rather than merely a problem of non-organic chest pain with some overlay of anxiety and depression. Despite some overlapping symptoms shared with persons who suffer from panic disorder, illness phobia, and extreme health anxiety, a number of central and defining features of cardiophobia are identified to differentiate cardiophobia from other anxiety disorders. An integrative model for understanding the origin and maintenance of cardiophobia (Eifert, 1990) is summarised and some treatment recommendations are derived from this model to target the central problems of persons with cardiophobia. Directions for future research are also discussed.

Human fear extinction and return of fear using reconsolidation update mechanisms: the contribution of on-line expectancy ratings

Disruption of the reconsolidation of conditioned fear memories has been suggested as a non-pharmacological means of preventing the return of learned fear in human populations. A reconsolidation update paradigm was developed in which a reconsolidation window is opened by a single isolated retrieval trial of a previously reinforced CS+ which is then followed by Extinction Training within that window. However, follow-up studies in humans using multi-methods fear conditioning indices (e.g., fear-potentiated startle, skin conductance, US-expectancy) have failed to replicate the retrieval+extinction effects. In the present study, we further investigated the retrieval+extinction reconsolidation update paradigm by directly comparing the acquisition, extinction, and return of fear-potentiated startle in the absence or presence of US-expectancy measures (using a trial-by-trial response keypad) with and without retrieval of a previously acquired CS-US association. Participants were fear conditioned to two visual cue CS+'s, one of which was presented as a single, isolated retrieval trial before Extinction Training and one that was extinguished as usual. The results show that the inclusion of US-expectancy measures strengthens the CS-US association to provide enhanced fear conditioning and maintenance of fear memories over the experimental sessions. In addition, in the groups that used on-line US-expectancy measures, the retrieval+extinction procedure reduced reinstatement of fear-potentiated startle to both previously reinforced CS+'s, as compared to the extinction as usual group.

An experimental test of the effects of parental modeling on panic-relevant escape and avoidance among early adolescents

Escape and avoidance behaviors play a prominent role in the maintenance and possibly development of panic disorder, yet the literature regarding the etiology of these emotion-regulation strategies is relatively underdeveloped. The current study experimentally tests hypotheses that parental modeling of escape during a well-established panic-relevant biological challenge increases panic-relevant escape and avoidance among offspring. Fifty physically and psychologically healthy early adolescents (28 females; Mage=11.58; 86% Caucasian), stratified by gender, were randomly assigned to observe one of their parents (39 females; Mage=40.04): either (a) model completing a 3-min voluntary hyperventilation exercise (no escape modeling group) or (b) model premature termination of a similar procedure (escape modeling group). Offspring in the escape modeling group demonstrated a stronger escape response by discontinuing their own challenge sooner than those in the no-escape modeling group (r=.70). No group differences emerged in terms of avoidance responding, as indexed by nearly identical responding in terms of delay time before initiating the challenge, respiration rate, and self-reported willingness to engage in a second proposed challenge. Results suggest that parental behaviors may play an important role in the development of some forms of panic-relevant responding. These preliminary findings may have important implications for future prevention programs targeting parents and at-risk youth.

Human fear acquisition deficits in relation to genetic variants of the corticotropin releasing hormone receptor 1 and the serotonin transporter

The ability to identify predictors of aversive events allows organisms to appropriately respond to these events, and failure to acquire these fear contingencies can lead to maladaptive contextual anxiety. Recently, preclinical studies demonstrated that the corticotropin-releasing factor and serotonin systems are interactively involved in adaptive fear acquisition. Here, 150 healthy medication-free human subjects completed a cue and context fear conditioning procedure in a virtual reality environment. Fear potentiation of the eyeblink startle reflex (FPS) was measured to assess both uninstructed fear acquisition and instructed fear expression. All participants were genotyped for polymorphisms located within regulatory regions of the corticotropin releasing hormone receptor 1 (CRHR1 - rs878886) and the serotonin transporter (5HTTLPR). These polymorphisms have previously been linked to panic disorder and anxious symptomology and personality, respectively. G-allele carriers of CRHR1 (rs878886) showed no acquisition of fear conditioned responses (FPS) to the threat cue in the uninstructed phase, whereas fear acquisition was present in C/C homozygotes. Moreover, carrying the risk alleles of both rs878886 (G-allele) and 5HTTLPR (short allele) was associated with increased FPS to the threat context during this phase. After explicit instructions regarding the threat contingency were given, the cue FPS and context FPS normalized in all genotype groups. The present results indicate that genetic variability in the corticotropin-releasing hormone receptor 1, especially in interaction with the 5HTTLPR, is involved in the acquisition of fear in humans. This translates prior animal findings to the human realm.

Neurogenesis and generalization: a new approach to stratify and treat anxiety disorders

Although an influence of adult neurogenesis in mediating some of the effects of antidepressants has received considerable attention in recent years, much less is known about how alterations in this form of plasticity may contribute to psychiatric disorders such as anxiety and depression. One way to begin to address this question is to link the functions of adult-born hippocampal neurons with specific endophenotypes of these disorders. Recent studies have implicated adult-born hippocampal neurons in pattern separation, a process by which similar experiences or events are transformed into discrete, non-overlapping representations. Here we propose that impaired pattern separation underlies the overgeneralization often seen in anxiety disorders, specifically post-traumatic stress disorder and panic disorder, and therefore represents an endophenotype for these disorders. The development of new, pro-neurogenic compounds may therefore have therapeutic potential for patients who display pattern separation deficits.

Seeking a spotless mind: extinction, deconsolidation, and erasure of fear memory

Learning to contend with threats in the environment is essential to survival, but dysregulation of memories for traumatic events can lead to disabling psychopathology. Recent years have witnessed an impressive growth in our understanding of the neural systems and synaptic mechanisms underlying emotional memory formation. As a consequence, interest has emerged in developing strategies for suppressing, if not eliminating, fear memories. Here, I review recent work employing sophisticated behavioral, pharmacological, and molecular tools to target fear memories, placing these memories firmly behind the crosshairs of neurobiologically informed interventions.

Unexpected arousal, anxiety sensitivity, and their interaction on CO₂-induced panic: further evidence for the context-sensitivity vulnerability model

The present experiment tested several predictions derived from the context-sensitivity vulnerability model of panic. Participants (N=79) scoring either high or low in anxiety sensitivity (AS) and with no history of unexpected panic were randomly assigned to one of two instructional sets: expected arousal (EA) or expected relaxation (ER). All participants were administered inhalation of room air and 35% CO(2) in a counterbalanced order. Consistent with theoretical predictions, High-AS participants who received ER instructions showed greater emotional responding compared to High-AS participants who received EA instructions, while instructional set did not affect responding among Low-AS participants. Panic attacks were observed in 52% of the High-AS-ER group compared to 17%, 5%, and 5% in the High-AS-EA, Low-AS-ER, and Low-AS-EA groups respectively. These findings are consistent with the theory's assertion that dispositional tendencies, such as anxiety sensitivity potentiate the panicogenic effects of threat-relevant context variables.

Effects of threat context and cardiac sensitivity on fear responding to a 35% CO2 challenge: a test of the context-sensitivity panic vulnerability model

The present study tested several predictions of a context-sensitivity panic vulnerability model emphasizing the interaction between threat context and threat sensitivities. Participants without a history of panic (N=47) completed both global and domain-specific panic relevant sensitivity measures and were then randomized to undergo a 35% CO2 inhalation challenge in the presence or absence of a cardiac defibrillator (threat context). As predicted by the model, cardiac sensitivity (but not trait anxiety or anxiety sensitivity) potentiated the effects of the presence of the defibrillator on CO2 fear responding. Moreover, as predicted by the model, the observed potentiation effects of cardiac sensitivity on CO2 fear responding were mediated by participants' threat appraisals connected to the presence of the defibrillator. Theoretical and clinical implications are discussed.

Catastrophic misinterpretations as a predictor of symptom change during treatment for panic disorder

OBJECTIVE

Cognitive models of panic disorder suggest that change in catastrophic misinterpretations of bodily sensations will predict symptom reduction. To examine change processes, we used a repeated measures design to evaluate whether the trajectory of change in misinterpretations over the course of 12-week cognitive behavior therapy is related to the trajectory of change in a variety of panic-relevant outcomes.

METHOD

Participants had a primary diagnosis of panic disorder (N = 43; 70% female; mean age = 40.14 years). Race or ethnicity was reported as 91% Caucasian, 5% African American, 2.3% biracial, and 2.3% "other." Change in catastrophic misinterpretations (assessed with the Brief Body Sensations Interpretation Questionnaire; Clark et al., 1997) was used to predict a variety of treatment outcomes, including overall panic symptom severity (assessed with the Panic Disorder Severity Scale [PDSS]; Shear et al., 1997), panic attack frequency (assessed with the relevant PDSS item), panic-related distress/apprehension (assessed by a latent factor, including peak anxiety in response to a panic-relevant stressor-a straw breathing task), and avoidance (assessed by a latent factor, which included the Fear Questionnaire-Agoraphobic Avoidance subscale; Marks & Mathews, 1979).

RESULTS

Bivariate latent difference score modeling indicated that, as expected, change in catastrophic misinterpretations predicted subsequent reductions in overall symptom severity, panic attack frequency, distress/apprehension, and avoidance behavior. However, change in the various symptom domains was not typically a significant predictor of later interpretation change (except for the distress/apprehension factor).

CONCLUSIONS

These results provide considerable support for the cognitive model of panic and speak to the temporal sequence of change processes during therapy.

A neuropeptide S receptor variant associated with overinterpretation of fear reactions: a potential neurogenetic basis for catastrophizing

Neuropeptide S (NPS) is a recently discovered G protein-coupled receptor ligand that modulates fear-like behaviors in rodents. A frequent A>T single-nucleotide polymorphism in the human NPS receptor gene NPSR1 confers a 10-fold higher efficacy of NPS signaling in vitro and has been linked with panic disorder (PD). We here report data from a classical fear-conditioning paradigm in healthy normal volunteers, in which carriers of the NPSR1 T allele evaluated their fear reactions to conditioned stimuli (CSs) as more pronounced than AA homozygous participants, although they did not show elevated peripheral-physiological conditioned responses (skin conductance responses-SCRs). T carriers also exhibited stronger CS-evoked brain activity in the rostral dorsomedial prefrontal cortex (dmPFC), an area that supports the explicit, conscious appraisal of threat stimuli. By contrast, more caudally situated mid-dmPFC, which has previously been associated with the generation of SCRs, showed no elevated response. Moreover, rostral dmPFC activation was correlated with participants' fear evaluations, further strengthening the link of this activation to increased individual fear appraisal. Our data suggest a genetic and neuroanatomical substrate for catastrophizing overinterpretations of fear reactions and provide a mechanistic explanation for the association between the NPSR1 T allele and PD.

Overgeneralization of conditioned fear as a pathogenic marker of panic disorder

OBJECTIVE

Classical conditioning features prominently in many etiological accounts of panic disorder. According to such accounts, neutral conditioned stimuli present during panic attacks acquire panicogenic properties. Conditioned stimuli triggering panic symptoms are not limited to the original conditioned stimuli but are thought to generalize to stimuli resembling those co-occurring with panic, resulting in the proliferation of panic cues. The authors conducted a laboratory-based assessment of this potential correlate of panic disorder by testing the degree to which panic patients and healthy subjects manifest generalization of conditioned fear.

METHOD

Nineteen patients with a DSM-IV-TR diagnosis of panic disorder and 19 healthy comparison subjects were recruited for the study. The fear-generalization paradigm consisted of 10 rings of graded size presented on a computer monitor; one extreme size was a conditioned danger cue, the other extreme a conditioned safety cue, and the eight rings of intermediary size created a continuum of similarity from one extreme to the other. Generalization was assessed by conditioned fear potentiating of the startle blink reflex as measured with electromyography (EMG).

RESULTS

Panic patients displayed stronger conditioned generalization than comparison subjects, as reflected by startle EMG. Conditioned fear in panic patients generalized to rings with up to three units of dissimilarity to the conditioned danger cue, whereas generalization in comparison subjects was restricted to rings with only one unit of dissimilarity.

CONCLUSIONS

The findings demonstrate a marked proclivity toward fear overgeneralization in panic disorder and provide a methodology for laboratory-based investigations of this central, yet understudied, conditioning correlate of panic. Given the putative molecular basis of fear conditioning, these results may have implications for novel treatments and prevention in panic disorder.

Caffeine challenge in patients with panic disorder: baseline differences between those who panic and those who do not

A proportion of patients with panic disorder (PD) display an increased sensitivity to the anxiogenic/panicogenic properties of caffeine. The aim of this study is to identify probable baseline differences between PD patients who panic and those who do not, after caffeine administration. In a randomized, double-blind, cross-over experiment performed in two occasions 3-7 days apart, 200 and 400 mg of caffeine, respectively, were administered in a coffee form to 23 patients with PD with or without Agoraphobia. Evaluations included the State-Trait Anxiety Inventory, the DSM-IV 'panic attack' symptoms (visual analogue scale form), the Symptom Checklist-90-Revised (SCL-90-R), as well as breath-holding (BH) duration, heartbeat perception accuracy and heart rate. Only those patients who did not present a panic attack after both challenges ('no panic group', N=14, 66.7%), and those who presented a panic attack after at least one challenge ('panic group', n=7, 33.3%) were included in the analysis. The panickers, compared to the non-panickers, presented at baseline: significantly higher total score of the SCL-90-R; significantly higher scores on all the SCL-90-R clusters of symptoms, except that of 'paranoid ideation'; significantly lower BH duration. The present preliminary findings indicate that PD patients who panic after a 200 mg or a 400 mg caffeine challenge, compared to the PD patients who do not panic after both of these challenges, may present at baseline significantly higher non-specific general psychopathology--as reflected in the SCL-90-R--and significantly shorter BH duration.

A caffeine challenge test in panic disorder patients, their healthy first-degree relatives, and healthy controls

Our aim was to observe the induction of anxiety symptoms and panic attacks by a caffeine challenge test in panic disorder (PD) patients (DSM-IV) and their healthy first-degree relatives. We randomly selected 25 PD patients, 27 healthy first-degree relatives of probands with PD, and 22 healthy volunteers with no family history of PD. In a randomized double-blind experiment performed over two occasions 7 days apart, 480 mg caffeine and a caffeine-free solution were administered in a coffee form. Using specific panic attack criteria, 52.0% (n=13) PD patients, 40.7% (n=11) first-degree relatives (chi2=1.81, df=1, P=0.179), and none of the control subjects had a panic attack after the test (chi2=51.7, df=2, P<0.001). In this caffeine challenge test, PD patients and their first-degree relatives were more sensitive than healthy volunteers to the panic attack symptoms but less sensitive to headache, increase in blood pressure, and insomnia. Our data suggest that there is an association between panic attacks after the intake of 480 mg of caffeine in PD patients and their first-degree relatives. There is a clear differentiation of PD patients and their first-degree relatives by a caffeine test from the healthy group.

Impaired discriminative fear-conditioning resulting from elevated fear responding to learned safety cues among individuals with panic disorder

Classical fear-conditioning is central to many etiologic accounts of panic disorder (PD), but few lab-based conditioning studies in PD have been conducted. One conditioning perspective proposes associative-learning deficits characterized by deficient safety learning among PD patients. The current study of PD assesses acquisition and retention of discriminative aversive conditioning using a fear-potentiated startle paradigm. This paradigm was chosen for its specific capacity to independently assess safety- and danger learning in the service of characterizing putative anomalies in each type of learning among those with PD. Though no group difference in fear-potentiated startle was found at retention, acquisition results demonstrate impaired discriminative learning among PD patients as indexed by measures of conditioned startle-potentiation to learned safety and danger cues. Importantly, this discrimination deficit was driven by enhanced startle-potentiation to the learned safety cue rather than aberrant reactivity to the danger cue. Consistent with this finding, PD patients relative to healthy individuals reported higher expectancies of dangerous outcomes in the presence of the safety cue, but equal danger expectancies during exposure to the danger cue. Such results link PD to impaired discrimination learning, reflecting elevated fear responding to learned safety cues.

Automatic associations and panic disorder: trajectories of change over the course of treatment

Cognitive models of anxiety and panic suggest that symptom reduction during treatment should be preceded by changes in cognitive processing, including modifying the anxious schema. The current study tested these hypotheses by using a repeated measures design to evaluate whether the trajectory of change in automatic panic associations over a 12-week course of cognitive behavior therapy (CBT) is related to the trajectory of change in panic symptoms. Individuals with panic disorder (N = 43) completed a measure of automatic panic associations--the Implicit Association Test (A. G. Greenwald, D. E. McGhee, & J. L. K. Schwartz, 1998), which reflects elements of the schema construct--every 3 weeks over the course of therapy and measures of panic symptoms each week. Dynamic bivariate latent difference score modeling not only indicated that automatic panic associations changed over the course of CBT for panic disorder but showed these changes were correlated with symptom reduction. Moreover, change in automatic panic associations was a significant predictor of change in panic symptom severity. These findings permit inferences about the temporality of change, suggesting that cognitive change does in fact precede and contribute to symptom change.

Mechanisms of change in cognitive therapy for panic disorder with agoraphobia

The purpose of this study was to test the predictions of an integrated cognitive and behavioral model of agoraphobic avoidance in patients with chronic panic disorder and agoraphobia during the process of observed therapeutic change. Treatment was residential with the majority (n=165, 88%) receiving cognitive therapy, while the remaining 23 (12%) received guided mastery therapy. The results of latent variable path modeling of the changes occurring over the course of this treatment suggested that the anxiety elicited by bodily sensations influenced catastrophic beliefs, which, in turn, increased avoidance. Avoidance increased the anxiety elicited by bodily sensations.

Interoceptive fear conditioning as a learning model of panic disorder: An experimental evaluation using 20% CO2-enriched air in a non-clinical sample

Despite the role afforded interoceptive fear conditioning in etiologic accounts of panic disorder, there are no good experimental demonstrations of such learning in humans. The aim of the present study was to evaluate the interoceptive conditioning account using 20% carbon dioxide (CO(2))-enriched air as an interoceptive conditioned stimulus (CS) (i.e., physiologically inert 5-s exposures) and unconditioned stimulus (US) (i.e., physiologically prepotent 15-s exposures). Healthy participants (N=42) were randomly assigned to one of three conditions: a CS-only, contingent CS-US pairings, or unpaired/non-contingent CS and US presentations. Electrodermal and self-report (e.g., distress, fear) served as indices of conditioned emotional responding. Results showed greater magnitude electrodermal and evaluative fear conditioning in the paired relative to the CS-only condition. The explicitly unpaired condition showed even greater electrodermal and evaluative responding during acquisition, and marked resistance to extinction. The latter results are consistent with the possibility that the unpaired procedure constituted a partial reinforcement procedure in which CO(2) onset was paired with more extended CO(2) exposure on 50% of the trials. Overall, the findings are consistent with contemporary learning theory accounts of panic.

Caffeine and 35% carbon dioxide challenge tests in panic disorder

Our aim was to compare the demographic and clinical features of panic disorder (PD) patients with agoraphobia-DSM-IV-who had a panic attack after both an oral caffeine and the 35% carbon dioxide (CO2) challenge tests (responsive group) and compare them with PD patients who did not have a panic attack after both tests (non-responsive group). We examined 83 PD patients submitted to a 35% CO2 test and to an oral caffeine (480 mg) intake within 1 week interval. A panic attack was induced in 51 (61.4%) patients during the CO2 test (chi2=31.67, df=1, p<0.001) and in 38 (45.8%) patients during the caffeine test (chi2=18.28, df=1, p=0.023). All patients who had a panic attack during the caffeine test also had a panic attack during the CO2 test (n=38)-responsive group. The responsive had more (chi2=24.55, df=1, p=0.008) respiratory PD subtype, disorder started earlier (Mann-Whitney, p<0.001) had a higher familial prevalence of PD (chi2=20.34, df=1, p=0.019), less previous alcohol abuse (chi2=23.42, df=1, p<0.001), and had more previous depressive episodes (chi2=27.35, df=1, p<0.001). Our data suggest that there is an association between respiratory PD subtype and hyperreactivity to challenge tests: CO2 and oral caffeine.

Caffeine challenge test in panic disorder and depression with panic attacks

Our aim was to observe if patients with panic disorder (PD) and patients with major depression with panic attacks (MDP) (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria) respond in a similar way to the induction of panic attacks by an oral caffeine challenge test. We randomly selected 29 patients with PD, 27 with MDP, 25 with major depression without panic attacks (MD), and 28 healthy volunteers. The patients had no psychotropic drug for at least a 4-week period. In a randomized double-blind experiment performed in 2 occasions 7 days apart, 480 mg caffeine and a caffeine-free (placebo) solution were administered in a coffee form and anxiety scales were applied before and after each test. A total of 58.6% (n = 17) of patients with PD, 44.4% (n = 12) of patients with MDP, 12.0% (n = 3) of patients with MD, and 7.1% (n= 2) of control subjects had a panic attack after the 480-mg caffeine challenge test (chi(2)(3) = 16.22, P = .001). The patients with PD and MDP were more sensitive to caffeine than were patients with MD and healthy volunteers. No panic attack was observed after the caffeine-free solution intake. The patients with MD had a lower heart rate response to the test than all the other groups (2-way analysis of variance, group by time interaction with Greenhouse-Geisser correction: F(3,762) = 2.85, P = .026). Our data suggest that there is an association between panic attacks, no matter if associated with PD or MDP, and hyperreactivity to an oral caffeine challenge test.

Repeated exposure to 20% CO2 challenge and risk for developing panic attacks: a controlled 6- and 12-month follow-up in a nonclinical sample

Among ethical concerns associated with biological challenge procedures is the risk of potentiating panic attacks in otherwise healthy persons who have no history of panic. The aim of the present study was to determine if repeated exposure to 20% CO2 challenge increases the risk of developing panic attacks in a nonclinical sample. One hundred and fifty-five (39.5%) of 392 participants who underwent a 20% CO2 challenge procedure and 51 (63.0%) of 81 controls who breathed only room air were evaluated for panic attacks using the Panic Attack Questionnaire-Revised both at 6 and 12 months after the experiment. The percentage of participants who developed subsequent panic attacks did not differ significantly between the CO2 challenge group and the room air controls. High dose CO2 challenge does not increase the risk of subsequent panic attacks in nonclinical populations; it is a safe paradigm for use in psychopathology research with healthy individuals.

Experimental induction of panic-like symptoms in patients with postural tachycardia syndrome

Patients with postural tachycardia syndrome (POTS) might be misdiagnosed with panic disorder due to shared clinical features. The first aim of our study was to investigate the relationship between symptoms of POTS and panic disorder. The second aim was to delineate clinical features distinguishing symptoms of POTS from panic disorder. A total of 11 patients with POTS and 11 control subjects participated in an IRB-approved, prospective, placebo-controlled study. The experimentally induced panic-like symptoms of POTS were systematically studied using the Acute Panic Inventory (API) questionnaire. The participants answered the questionnaire after each placebo infusion and after each of the three provoking stimuli: head-up tilt test (HUT), isoproterenol infusion (ISI), and sodium lactate infusion (SLI). API responses were summed for each subject at each time point of administration. Individual API symptoms and summed responses were analyzed for statistical significance. All patients with POTS developed symptoms of orthostatic intolerance during HUT. Pharmacologically induced symptoms subjectively mimicked spontaneous symptoms in 5 of 11 patients during ISI and in none of 11 patients during SLI. In contrast, API scores in these patients reached panic threshold in 0 of 11 following HUT, in 4 of 11 following ISI and in 4 of 11 following SLI. Individual symptoms analysis revealed that significant increase in scores was limited to the somatic symptoms of palpitations, dyspnea, and twitching or trembling. In conclusion, the symptoms of POTS are phenomenologically different and clinically distinguishable from panic disorder symptoms.

Avoidance behavior in panic disorder: The moderating influence of perceived control

The relations among anxiety sensitivity, perceived control, and agoraphobia were examined in 239 patients diagnosed with panic disorder (PD). Most patients exhibited agoraphobia accompanying their PD (98% situational avoidance; 90% experiential avoidance; and 80% endorsed interoceptive fear and avoidance). Anxiety sensitivity and perceived emotional control were associated with agoraphobia, and perceived threat control was found to moderate the relationship between anxiety sensitivity and agoraphobia. Lower levels of perceived control were associated with a stronger relationship between anxiety sensitivity and agoraphobia. Results were consistent for self-reported and clinician-rated agoraphobia. Implications for the role of perceived control in agoraphobia development and treatment are discussed.

Fear extinction in rodents: basic insight to clinical promise

Fear extinction, the reduction of fear by repeated exposure to the object of fear, is a crucial paradigm of inhibitory learning and the acknowledged preclinical model for behavior therapy of human anxiety. Recent insights have clarified roles for infralimbic prefrontal cortex, hippocampus and periaqueductal gray in extinction learning, while maintaining a central role for the basolateral amygdaloid nucleus in the acquisition and storage of this learning. Simultaneously, molecular insights have implicated several neurotransmitter and second messenger systems in extinction learning, and revealed that extinction is surprisingly easy to improve, yielding the promise of a novel approach to improved psychiatric treatments for a variety of human anxiety disorders.

Extinction in multiple contexts does not necessarily make extinction less vulnerable to relapse

Three fear-conditioning experiments with rat subjects examined the effects of extinction in multiple contexts on a final relapse (renewal) effect that occurred when the extinguished fear cue was tested in a new context (Experiments 1 and 3) or in the context in which fear conditioning had first occurred (Experiment 2). Rats that received extinction in three contexts demonstrated more fear during extinction than rats that received the same number and temporal distribution of extinction trials in one context; extinction was partially lost with each context switch. Although extinction in multiple contexts thus had an impact on extinction behavior, it did not reduce the size of the final renewal effect. Fear during extinction was occasionally positively correlated with fear during final testing, but the two were never negatively correlated. The results suggest that extinction in multiple contexts does not necessarily weaken fear renewal, and that extinction procedures that generate high levels of responding in extinction do not necessarily make extinction learning less context-specific.

The L-type calcium channel blocker nifedipine impairs extinction, but not reduced contingency effects, in mice

We recently reported that fear extinction, a form of inhibitory learning, is selectively blocked by systemic administration of L-type voltage-gated calcium channel (LVGCC) antagonists, including nifedipine, in mice. We here replicate this finding and examine three reduced contingency effects after vehicle or nifedipine (40 mg/kg) administration. In the first experiment, contingency reduction was achieved by adding USs to the training protocol (degraded contingency), a phenomenon thought to be independent of behavioral inhibition. In the second experiment, contingency reduction was achieved by varying the percentage of CS-US pairing, a phenomenon thought to be weakly dependent on behavioral inhibition. In the third and fourth experiments, contingency reduction was achieved by adding CSs to the training protocol (partial reinforcement), a phenomenon thought to be completely dependent on behavioral inhibition. We found that none of these reduced contingency effects was impaired by nifedipine. In a final experiment, we found that extinction conducted 1 or 3 h post-acquisition, but not immediately, was LVGCC-dependent. Taken together, the results suggest that reduced contingency effects and extinction depend on different molecular mechanisms and that LVGCC dependence of behavioral inhibition develops with time after associative CS-US learning.

Systemic blockade of D2-like dopamine receptors facilitates extinction of conditioned fear in mice

Extinction of conditioned fear in animals is the explicit model of behavior therapy for human anxiety disorders, including panic disorder, obsessive-compulsive disorder, and post-traumatic stress disorder. Based on previous data indicating that fear extinction in rats is blocked by quinpirole, an agonist of dopamine D2 receptors, we hypothesized that blockade of D2 receptors might facilitate extinction in mice, while agonists should block extinction, as they do in rats. One day after fear conditioning mice with three pairings of a white noise conditional stimulus (CS) with moderate footshock, we injected the D2 antagonist, sulpiride, the D2 agonist, quinpirole, or vehicle, just before repeated CS presentations to generate extinction. We assayed fear by measuring behavioral freezing during extinction presentations and then drug-free during CS presentations 1 d later. We found that sulpiride injections before extinction training facilitated extinction memory 24 h later, while quinpirole partially blocked extinction memory compared with vehicle-injected controls. Notably, sulpiride treatment yielded significant extinction after spaced CS presentations, which yield no extinction at all in vehicle-treated mice. These findings suggest that dopamine D2-mediated signaling contributes physiological inhibition of extinction, and that D2 antagonists may be useful adjuncts to behavior therapy of human anxiety disorders.

Is premenstrual dysphoria a variant of panic disorder? A review

Patients with premenstrual dysphoric disorder (PMDD) and patients with panic disorder (PD) both experience high rates of panic attacks in laboratory panic provocation studies. Recently, this shared elevated rate of challenge-induced panic has received increasing attention. Researchers have suggested that PMDD and panic disorder may share a pathophysiological or psychobiological link. The purpose of this paper is to review the findings from PMDD challenge studies and the theories advanced to connect PMDD to panic disorder. Taken together, the results of the PMDD challenge studies confirm that agents that incite panic in PD patients do so as well in PMDD women. This shared elevated challenge-induced panic cannot be accounted for by explanations such as a history of PD in PMDD women. None of the physiological theories as currently expressed--suffocation false alarm, gamma-aminobutyric acid (GABA), noradrenergic, serotonergic, and cholecystokinin--yet provides a compelling candidate to account for shared elevated challenge-induced panic in PD and PMDD patients. Psychological perspectives on panic emphasize that bodily sensations themselves can cause fear. Researchers have yet to apply several influential psychological approaches--conditioning, catastrophic misinterpretation, and anxiety sensitivity--to PMDD patients. Because psychological factors influence anxious responding in challenge studies, the search for the biological abnormality best accounting for PMDD panic might benefit from a reframing of the question to one that considers the psychological perspective as well.

Are Current Theories of Panic Falsifiable?

The authors examine 6 theories of panic attacks as to whether empirical approaches are capable of falsifying them and their heuristic value. The authors conclude that the catastrophic cognitions theory is least falsifiable because of the elusive nature of thoughts but that it has greatly stimulated research and therapy. The vicious circle theory is falsifiable only if the frightening internal sensations are specified. The 3-alarms theory postulates an indeterminate classification of attacks. Hyperventilation theory has been falsified. The suffocation false alarm theory lacks biological parameters that unambiguously index dyspnea or its distinction between anticipatory and panic anxiety. Some correspondences postulated between clinical phenomena and brain areas by the neuroanatomical hypothesis may be falsifiable if panic does not depend on specific thoughts. All these theories have heuristic value, and their unfalsifiable aspects are capable of modification.

Adrenergic transmission facilitates extinction of conditional fear in mice

Extinction of classically conditioned fear, like its acquisition, is active learning, but little is known about its molecular mechanisms. We recently reported that temporal massing of conditional stimulus (CS) presentations improves extinction memory acquisition, and suggested that temporal spacing was less effective because individual CS exposures trigger two opposing processes: (1) fear extinction, which is favored by CS massing, and (2) fear incubation (increase), which is favored by spacing. We here report the effects of manipulating the adrenergic system during massed or spaced CS presentations in fear-conditioned mice. We administered yohimbine (5 mg/kg), an alpha(2)-receptor antagonist, or propranolol (10 mg/kg), a beta-receptor antagonist, systemically prior to CS presentation sessions and recorded both short- and long-term changes in conditional freezing. Yohimbine treatment facilitated extinction of both cue and context fear with massed protocols. When given before spaced CS presentations, propranolol led to a persistent incubation of cue fear, whereas yohimbine led to persistent extinction, compared with vehicle-treated animals, which showed no change in fear. These results suggest that norepinephrine positively modulates the formation of fear extinction memories in mice. They also provide clear evidence that spaced CS presentations trigger both fear-reducing (extinction) and fear-increasing (incubation) mechanisms.

Mechanism of Change in Cognitive-Behavioral Treatment of Panic Disorder: Evidence for the Fear of Fear Mediational Hypothesis

Numerous clinical trials have demonstrated the efficacy of cognitive-behavioral treatment (CBT) for panic disorder. However, studies investigating the mechanisms responsible for improvement with CBT are lacking. The authors used regression analyses outlined by R. M. Baron and D. A. Kenny (1986) to test whether a reduction in fear of fear (FOF) underlies improvement resulting from CBT. Pre- and posttreatment measures were collected from 90 CBT-treated patients and 40 wait-list control participants. Overall, treatment accounted for 31% of the variance in symptom reduction. The potency of FOF as a mediator varied as a function of symptom facet, as full mediation was observed for the change in global disability, whereas the effects of CBT on agoraphobia, anxiety, and panic frequency were partially accounted for by reductions in FOF. Clinical implications and future research directions are discussed.

The conditioning of dyspneic suffocation fear. Effects of carbon dioxide concentration on behavioral freezing and analgesia

Previous studies in our laboratory have shown that a single exposure to 100% carbon dioxide (CO2) can serve as an effective unconditioned stimulus (US) in a Pavlovian aversive-context conditioning paradigm in rats. Although the US exposure parameters employed in the initial studies were sufficient for producing a context-specific enhancement of behavioral freezing and analgesia, it had yet to be determined whether variations of these CO2 conditioning procedures would produce other conditioning effects. Thus, the purpose of the following experiment was to investigate the intensity of the US on the conditioned response (CR). The findings confirm that variations in CO2 concentrations produce changes in the CR that are consistent with principles of Pavlovian conditioning. The findings lend additional support to the tenability of a dyspneic suffocation fear theory of panic disorder, a theory that postulates that at least one type of panic attack could be a consequence of Pavlovian conditioning.

Breathing training for treating panic disorder. Useful intervention or impediment?

Breathing training (BT) is commonly used for treatment of panic disorder. We identified nine studies that reported the outcome of BT. Overall, the published studies of BT are not sufficiently compelling to allow an unequivocal judgment of whether such techniques are beneficial. This article discusses problems with the underlying rationale, study design, and techniques used in BT, and it identifies factors that may have determined therapy outcomes. The idea that hypocapnia and respiratory irregularities are underlying factors in the development of panic implies that these factors should be monitored physiologically throughout therapy. Techniques taught in BT must take account of respiration rate and tidal volume in the regulation of blood gases (pCO2). More studies are needed that are designed to measure the efficacy of BT using an adequate rationale and methodology. Claims that BT should be rejected in favor of cognitive or other forms of intervention are premature.

Rodent doxapram model of panic: behavioral effects and c-Fos immunoreactivity in the amygdala

BACKGROUND

Panic attacks, the hallmark of panic disorder, are often characterized by hyperventilation. Existing animal models of anxiety have not addressed the effects of the hyperventilation on anxiety-related behaviors. Doxapram is a respiratory stimulant that reliably evokes panic attacks in patients with panic disorder. We examined doxapram in four rodent models of anxiety and sought to identify brain regions involved in its behavioral effects.

METHODS

The effects of doxapram were determined for cue and contextual fear conditioning, the open field test, and the social interaction test. The effect of doxapram on c-Fos-like immunoreactivity was examined in three brain regions.

RESULTS

Doxapram at 4 mg/kg increased anxiety-related behaviors in all four anxiety models. An inverted U-shaped dose-response curve was identified for fear conditioning to cue. Doxapram induced c-Fos-like immunoreactivity in the central nucleus of the amygdala but not the lateral nucleus or the nucleus tractus solitarius.

CONCLUSIONS

Doxapram enhanced anxiety-related behaviors in four animal models of anxiety that involve conditioning or spontaneous avoidance. The effect of doxapram may result from activation of neurons in the amygdala. Doxapram, by inducing hyperventilation, may be a useful adjunct to existing animal anxiety models for improving validity for panic anxiety.

Unconscious amygdalar fear conditioning in a subset of chronic fatigue syndrome patients

Here, a novel hypothesis for chronic fatigue syndrome (CFS) is proposed. CFS may be a neurophysiological disorder focussing on the amygdala. During a 'traumatic' neurological event often involving acute psychological stress combined with a viral infection or other chemical or physiological stressor, a conditioned network or 'cell assembly' may be created in the amygdala. The unconscious amygdala may become conditioned to be chronically sensitised to negative symptoms arising from the body. Negative signals from the viscera or physiological, chemical and dietary stressors, become conditioned stimuli and the conditioned response is a chronic sympathetic outpouring from the amygdala via various brain pathways including the hypothalamus. This cell assembly then produces the CFS vicious circle, where an unconscious negative reaction to symptoms causes immune reactivation/dysfunction, chronic sympathetic stimulation, leading to sympathetic dysfunction, mental and physical exhaustion, and a host of other distressing symptoms and secondary complications. And these are exactly the symptoms that the amygdala and associated limbic structures are trained to monitor and respond to, perpetuating a vicious circle. Recovery from CFS may involve projections from the medial prefrontal cortex to the amygdala, to control the amygdala's expressions. I shall firstly discuss predisposing, precipitating, and perpetuating factors involved in the possible etiology of chronic fatigue syndrome (CFS), followed by the patient's experience of the illness. Finally, I shall look at a suggested explanation for the symptoms of CFS.

A general anxiety-prone cognitive style in anxiety disorders

OBJECTIVE

This study compared scores on the Anxious Thoughts & Tendencies (AT&T) questionnaire, a putative measure of a general anxiety-prone cognitive style, among patients with panic disorder without agoraphobia (PD, n=62), panic disorder with agoraphobia (PDA, n=29), generalized anxiety disorder (GAD, n=43), limited social phobia (LSP, n=34), generalized social phobia (GSP, n=33), and community residents (n=319).

METHOD

Candidates for treatment studies completed a diagnostic interview and the AT&T. AT&T scores were compared among anxious groups using analysis of variance. Then depressed and non-depressed patients were compared. The final analysis compared anxious groups without comorbid depressive or anxiety disorders.

RESULTS

AT&T scores were highest in PDA patients, followed by patients with GAD or GSP, then patients with PD or LSP, with community residents lowest. Depressed patients were higher than non-depressed patients. Patients with current or past comorbid depressive disorders did not differ. The ranking of anxious groups on AT&T scores remained unchanged after exclusion of patients with comorbid disorders. Patients with PD or LSP without comorbidity had the same AT&T levels as the community sample.

CONCLUSIONS

The AT&T discriminates PDA and GAD from PD per our hypothesis. The low AT&T levels among patients with PD and LSP suggest no association with a general anxiety-prone cognitive style. LSP and GSP may be distinct disorders. The cognitive style assessed by the AT&T is also associated with depression and may be a marker for vulnerability to depression. Definitive conclusions about a pathogenic role for cognitions require their measurement before the onset of the disorder.