Emotional variability and sustained arousal during exposure

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Abstract

Background and objectives

In traditional exposure therapy for phobias and anxiety disorders, reduction of fear responding is used as an index of learning. However, recent evidence in animal models suggests that sustained arousal and enhanced fear responding throughout exposure may actually predict better long-term outcomes (Rescorla, 2000).

Methods

The effects of sustained arousal during exposure were investigated in a clinical analog sample of 59 participants fearful of public speaking. Participants completed exposure with or without the presence of additional excitatory stimuli which were intended to enhance arousal and fear responding throughout exposure.

Results

Group assignment (exposure versus exposure with additional excitatory stimuli) did not significantly predict outcome at 1-week follow-up testing, as measured physiologically, subjectively, and behaviorally. A set of regression analyses investigating whether any exposure process measures predicted outcome indicated that sustained arousal throughout exposure as well as variability in subjective fear responding throughout exposure (e.g., Kircanski et al., 2011) predicted lower levels of fear at follow-up testing (p < 0.05; p < 0.001) after controlling for demographic variables as well as pre-exposure fear levels.

Limitations

The excitatory stimuli used failed to produce the intended effects. However, some participants did maintain elevated arousal throughout exposure and this predicted better outcomes at 1-week follow-up testing.

Conclusions

Sustained arousal throughout exposure as well as variability in subjective fear responding during exposure may be better predictors of long-term outcomes than habituation of fear across exposure.

Highlights

► Habituation of fear across exposure may not be the best indicator of learning. ► Sustained fear responding throughout exposure may facilitate long-term learning. ► Emotional variability during exposure predicted less return of fear at follow-up.

Introduction

A large body of literature supports the effectiveness of exposure therapy for the treatment of anxiety disorders and phobias (e.g., Norton & Price, 2007). Anxiety disorders are characterized by avoidance of feared stimuli and this avoidance perpetuates the fear: each time the individual avoids the fearful stimulus, he or she reinforces the belief that avoidance is the key to remaining safe. Exposure exercises force the individual to test the hypothesis that facing the fearful stimuli will not lead to catastrophic results. During exposure therapy, the individual learns that nothing aversive occurs while in the presence of the fearful stimuli; therefore, fear of the stimuli decreases. Thus, extinction learning is believed to be one mechanism underlying the effectiveness of exposure therapy (Eelen & Vervliet, 2006).

However, not every recipient of exposure therapy benefits (non-response rates roughly vary from 10 to 30% depending on the anxiety disorder; see Craske, 1999). In addition, even for those who do benefit, fear responding can sometimes return (Craske & Mystkowski, 2006). In fact, it is now well understood that extinction does not involve the unlearning of the previous fear association but, rather, new learning. That is, rather than being a passive process, extinction is an inhibitory but active form of learning (Bouton, 1993). Thus, even though extinction can eliminate fearful responding, the original fear learning is intact and retrievable as demonstrated by various procedures including changing the test context (renewal; Bouton, 1993), presenting unsignaled USs (reinstatement; Rescorla & Heth, 1975), or simply allowing time to pass (spontaneous recovery; Baum, 1988). The fact that the fear memory appears to remain intact even after extinction learning occurs can be problematic for treatment. Individuals may successfully complete exposure therapy only to experience subsequent return of fear. Thus, investigations aimed at finding methods for enhancing exposure-based interventions are warranted in order to increase response rates and decrease the likelihood of return of fear following successful treatment.

Investigations using animal models to explore methods for enhancing extinction learning may provide insight into methods for increasing the effectiveness of exposure therapy (Hermans, Craske, Mineka, & Lovibond, 2006). In nonprimate samples, Rescorla (2000) demonstrated that extinction of a conditional stimulus (CS) in the presence of additional excitatory stimuli was superior to extinction alone. Although fear responding during extinction was greater when the CS underwent extinction training in the presence of an additional excitatory stimulus, these rats demonstrated significantly less fear responding to that CS at follow-up testing. Thus, additional excitatory stimuli during extinction training increase fear responding during extinction but also facilitate long-term fear reduction. Rescorla (2000) posits potential mechanisms for these results including: 1) that when the CS is presented with another excitatory stimulus, the discrepancy between expectation (i.e., of the US) and reality (i.e., no US) is maximized, which facilitates learning according to error-correction models (e.g., Rescorla & Wagner, 1972) and 2) when the CS is presented with another excitatory stimulus, fear responding increases and this itself might generate more extinction learning2.

There is evidence that increased responding alone may optimize learning during extinction. This evidence comes from investigations involving adrenergic neurotransmission. The adrenergic system has been implicated in the acquisition and consolidation of emotional memories in animals (Cahill, Pham, & Setlow, 2000) and humans (Nielson & Jensen, 1994). In fact, adrenergic hyperactivity has been implicated in anxiety disorders (e.g., Southwick, Morgan, Charney, & High, 1999). Thus, Cain, Blouin, and Barad (2004) hypothesized that enhanced adrenergic transmission would retard extinction learning. In other words, they predicted that enhanced arousal and elevated fear responding during extinction would lead to less learning during extinction. To test this, they administered yohimbine (which blocks autoinhibitory α2 adrenergic receptors and is anxiogenic in humans) prior to extinction. Their results indicated the opposite effect – administration of yohimbine facilitated extinction learning. The authors posited several possible mechanisms for these results including that increased adrenergic activity promotes consolidation of emotional memories (Cahill et al., 2000, Cahill et al., 1994, Nielson and Jensen, 1994) so it is possible that administration of yohimbine facilitated consolidation of extinction memories. Thus, enhanced arousal and increased fear responding during extinction may itself enhance extinction learning.

In fact, some studies have demonstrated that procedures designed to maintain arousal throughout exposure may facilitate long-term fear reduction. For example, pharmacological procedures which inhibit arousal, if administered during exposure, have been shown to impede extinction learning in rats (Berman & Dudai, 2001). The findings of Cain et al. (2004), taken together with those presented by Rescorla (2000), suggest that greater arousal and elevated fear responding may actually facilitate learning during exposure therapy. The association between elevated fear responding during extinction training and greater fear reduction at retest is at odds with the tenets of Emotional Processing Theory (EPT; Foa and Kozak, 1986, Foa and McNally, 1996), a widely used model for exposure therapy. EPT posits that both within-session habituation and between-session habituation3 of fear are necessary for long-term fear reduction. However, these premises of EPT have not been well supported by the evidence (for review, see Craske et al., 2008).

The goal of the present study was to directly investigate whether the presence of additional excitatory and arousing stimuli throughout exposure facilitates long-term fear reduction. It was expected that the presence of such stimuli would lead to elevated fear responding and enhanced arousal throughout exposure, thus providing a test of whether maintaining elevated fear throughout exposure facilitates long-term fear reduction. This investigation utilized a clinical analog sample of participants highly fearful of public speaking. Two excitatory stimuli were chosen to be presented during exposure exercises; participants were exposed to both of the excitatory stimuli concurrently throughout exposure, both of the excitatory stimuli but sequentially throughout exposure, or none of the excitatory stimuli. Based on the findings of Rescorla (2000) and Cain et al. (2004), participants exposed to no excitors were hypothesized to demonstrate more return of fear at follow-up testing as compared with those participants who were presented with excitors (concurrently or sequentially) during exposure. Additionally, participants presented with the two excitors sequentially during exposure were hypothesized to demonstrate less return of fear at follow-up testing as compared with participants presented with the two excitors concurrently. This is due to the expectation that the novelty of adding an excitor will cause an increase in arousal; thus, participants in the sequential excitors group will experience more increases in arousal since the second excitor is added in halfway through each speech versus those in the concurrent excitor group who are presented with both excitors throughout each exposure exercise.

Section snippets

Design

Participants fearful of public speaking were randomly assigned to one of three experimental groups: Concurrent [C], n = 21; Sequential [S], n = 20; or No [N], n = 18 excitors during exposure. These three groups were compared across three time points: Baseline (prior to exposure), Test-1 (immediately following exposure), and Test-2 (one week following exposure).

Participants

Fifty-nine participants (44 females, 15 males), highly fearful of public speaking, with a mean age of 19.5 (range 18–25), were recruited

Baseline

Means on both subscales of the SSPS confirmed that the screening measure was effective in selecting a sample of participants highly fearful of public speaking (SSPS-P = 12.93; SSPS-N = 12.19), although the mean on the PRCS (7.38) was not above the clinical cutoff score. Participants were only included if they reported a fear level of at least 40 on the SUD scale during the Baseline BAT; the average maximum SUDS rating during the Baseline BAT was 59.78 (on a 0–100 scale). Mean heart rate at

Discussion

These results partially supported the study hypotheses. The excitatory stimuli used in the current design did not produce distinct groups in regards to fear arousal throughout exposure. We had predicted that the participants presented with no excitors would demonstrate the lowest level of fear responding during exposure, the group presented with concurrent excitors would demonstrate a significantly higher level of fear responding during exposure, and that the group presented with sequential

Role of the funding source

This research was supported in part by National Institute of Mental Health grant R21 MH722 59-01 granted to Mark Barad and Michelle Craske. The funding source had no involvement in the study design; the collection, analysis, or interpretation of data; the writing of the report; or the decision to submit the paper for publication.

Conflict of interest

There is no conflict of interest to be declared for any of the authors of this article.

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    Present address: 238 Burnett Hall, University of Nebraska-Lincoln, Lincoln, NE 68588-0308, USA.

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