Invited Essay
Optimizing inhibitory learning during exposure therapy

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Abstract

Prevailing models of exposure therapy for phobias and anxiety disorders construe level of fear throughout exposure trials as an index of corrective learning. However, the evidence, reviewed herein, indicates that neither the degree by which fear reduces nor the ending fear level predict therapeutic outcome. Developments in the theory and science of fear extinction, and learning and memory, indicate that ‘performance during training’ is not commensurate with learning at the process level. Inhibitory learning is recognized as being central to extinction and access to secondary inhibitory associations is subject to influences such as context and time, rather than fear during extinction training. Strategies for enhancing inhibitory learning, and its retrieval over time and context, are reviewed along with their clinical implications for exposure therapy and directions for future research.

Introduction

The primary goal of this paper is to address the gap between advances in the basic science of extinction learning and memory on the one hand, and models and methods of exposure therapy for phobias and anxiety disorders on the other hand. The argument to be made is that the customary reductions in reported fear and physiological arousal throughout exposure therapy are not evidence for corrective learning. Therapeutic efforts are better directed towards toleration of distress within a structure that enhances the consolidation and retrievability of exposure-based inhibitory learning over context and time. The goal is not to question the necessity of exposure therapy for phobias and anxiety disorders; it is already well established that phobias and anxiety disorders respond positively to approaches such as cognitive therapy (e.g., Norton & Price, 2007) and medications (e.g., Roy-Byrne & Cowley, 2002) as well as exposure-based therapies. Rather, the goal is to update conceptualizations of the mechanisms underlying exposure therapy.

The first of two lines of basic science research from which we draw is extinction learning, since the extinction of conditioned fear can be viewed as a laboratory analogue for exposure therapy (Bouton, Mineka, & Barlow, 2001; Davey, 1997; Eelen, Hermans & Baeyens, 2001; Mineka, 1985).1 Knowledge of the mechanisms underlying extinction learning, and the resultant conditions that facilitate or hamper extinction learning, may help to sharpen exposure treatments and maximize outcomes in both the short and long run (i.e., relapse prevention). Indeed, extinction learning has served as the explicit model of behavior therapy for phobias for many years (see Eelen & Vervliet, 2006), and extinction-like processes continue to be emphasized, albeit in ways that lag behind recent advances.

The second line of basic science research pertains to learning and memory, since what is learned throughout exposure therapy is intended to be remembered in different places and at later points in time once exposure therapy is over. The evidence pertaining to the retrieval strength of learning, presented cogently in the ‘new theory of disuse’ (Bjork & Bjork (1992), Bjork & Bjork (2006)), has relevance to the long-term outcomes from exposure therapy. Naturally, this line of research overlaps with the science of extinction learning.

Before discussing these advances, we overview the prevailing model of exposure therapy for phobias and anxiety disorders, which purports that fear levels throughout exposure therapy are reflective of learning and are critical to overall therapeutic outcome.

Section snippets

Emotional processing theory

The concept of habituation (e.g., Groves & Thompson, 1970) was combined with the concept of ‘corrective learning’ to explain the effects of exposure therapy in the widely known ‘emotional processing’ theory (EPT), initiated by Rachman (1980), extensively expanded by Foa and Kozak (1986) and subsequently revised to take into account developments in context specificity of extinction (Foa & McNally, 1996). EPT purports that the effects of exposure therapy derive from activation of a ‘fear

Fear activation, within-session and between-session habituation as indices of learning?

IFA is operationalized as the peak response during the first exposure trial, or the first part thereof, where peak is defined as maximum fear levels (self-report or physiology) minus baseline levels (e.g., Kozak, Foa, & Steketee, 1988).2 WSH is measured as the difference between

Fear expression versus fear learning

The emphasis upon fear reduction within an exposure trial (i.e., ‘remain in the context until fear has declined’) assumes that performance during training is commensurate with learning. That is, EPT purports that continued fear by the end of exposure represents continued erroneous evaluation of the probability of danger or negative valence of the stimulus (Foa & Kozak, 1986; Foa & McNally, 1996). Whereas downshifting of the probability of danger or the negative valence of target stimuli may

Mismatch with expectancies

Expectancies for the likelihood of aversive events are central to human fear conditioning. For example, contingency awareness (i.e., knowledge that a specific CS predicts a specific US), although of debatable necessity for conditioned responding (e.g., Lovibond and Shanks (2002) versus Ohman and Mineka (2001)) is a strong correlate of conditioned responding (e.g., Purkis & Lipp, 2001). In turn, extinction is posited to follow from a mismatch between the expectancy of an aversive event and the

Variability throughout exposure

In general, retention of learned non-emotional material is enhanced by random and variable practice (Magill & Hall, 1990). Even though variation increases difficulty throughout learning, Bjork & Bjork (1992), Bjork & Bjork (2006) proposed that variation enhances long-term outcome. According to their model, variation increases the storage strength of information to be learned by making retrieval of past learning easier via the availability of cues that were present during prior learning. In

Conclusions

Reliance upon fear levels throughout exposure therapy as an index of learning is not only lacking empirical support, but assumes that performance during ‘instruction’ is a reliable index of learning; an assumption that is not supported by learning and memory research. Inhibitory processes are now recognized as being central to extinction learning, and evocation of such processes at the time of re-exposure to a previously feared stimulus largely shapes the level of fear, regardless of how much

Acknowledgments

This work was supported by a grant from the National Institutes of Health to Drs. Barad and Craske (MK30488).

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