Part 2: Habituation during ERP treatment: Always appreciated, never expected

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In part 1 of our series Habituation: Always appreciated, never expected, we reviewed the history of Exposure and Response Prevention treatment (ERP), including an exploration into how emotional processing theory (EPT) was suggested as the mechanism which explains how ERP works in treating obsessive-compulsive disorder (OCD). 

In part 1, we reviewed the idea that EPT works by activating a fear structure and then presenting that fear structure with new information incompatible with it. The new information would cause the fear structure to be transformed or destroyed. This transformation or destruction of the fear structure would result in reduction of symptoms and successful treatment. 

Also in part 1, we reviewed the ways to identify successful emotional processing. Three components were signs of successful emotional processing:

1. Activation of the fear structure (e.g., self reports of anxiety, physiological activation)

2. Within-session habituation (e.g., over the course of a 50 minute session with a therapist, the fear initially activated by touching the trash can reduces)

3. Across-session habituation (e.g., reports of decreased anxiety and decreased physiological activation when touching trash cans in the future)

These three components were thought to be individually necessary and work together in treating OCD. This is why Foa and Kozak wrote: “...obsessive-compulsives who failed to habituate within sessions also failed to habituate across sessions, suggesting that the two processes are not independent: Long-term habituation [across session habituation] must be preceded by short-term habituation [within-session habituation]” (p. 29).¹ 

But, at the end of part 1, I again emphasized that habituation during an exposure is not necessary for successful treatment. How come I would write this, given that Foa and Kozack have stated, and backed up with evidence, that habituation is a necessary feature of ERP treatment? That’s what we’ll begin to review below.

The first, and easiest to follow, reason that I emphasized that habituation during an exposure is not necessary for successful treatment, even though Foa and Kozack argued that exposure is necessary for successful treatment, is that Foa’s views have changed. 

In 2006, Foa and her co-authors reviewed that, in the 1980s, Foa did promote the view that within session habituation was a necessary indicator of successful emotional processing and, thus, the pathway to successful treatment. However, Foa and her co-authors went on to explain that they’d revised these views because “...most studies have not found a direct relationship between within-session habituation and symptom reduction” (p. 9).²

A decade later, In 2016, Foa and McLean wrote that “...the role of within-session extinction in treatment outcomes has not received strong support. Indeed…within-session fear reduction is not related to fear extinction and long-term fear reduction” (p. 11).³ And, in 2023, Foa and her co-authors again reported that “...the degree of within-session habituation is not consistently associated with [treatment] outcome” (p. 280).⁴

In 1986, Foa argued that within-session habituation was a necessary ingredient of successful ERP. Yet, in the decades that followed, Foa, again and again, claimed that within-session habituation, while nice to have, was not a necessary ingredient of successful change.

What prompted Foa to change her mind? 

Comparing theories and hypotheses

Like any good scientist, Foa was consistently comparing her theories and hypotheses with the available data. Foa’s original EPT model was based on data which seemed to demonstrate that within-session habituation was a reliable and necessary predictor of between-session habituation. In other words, that a client’s habituation within an exposure session was a reliable and necessary indicator that the client would experience overall symptom reduction in their life (i.e., successful treatment). 

But, as more controlled trials of ERP were conducted, more data was identified which undercut the idea that within session habituation was a requirement of successful treatment. For example, in 1988, Kozak, Foa, and Steketee conducted a controlled ERP trial that found that within-session habituation was not related to long-term treatment outcome.⁵ That is, whether or not a client habituated within their exposure sessions was not related to the client’s long-term treatment outcome (reduced anxiety at the end of treatment).

Interestingly, the finding that within-session habituation was not related to long-term treatment outcome, was found in many other controlled studies across the anxiety disorders, including PTSD, panic disorder, and phobias.⁶⁷⁸

In all of these studies, although participants, on average, did not achieve substantial within-session habituation (e.g., they were still feeling anxious at the end of the exposure session), the participants experienced substantial between-session habituation and positive treatment outcomes (e.g., the participants experienced significant symptom reduction and generally successful treatment in the long-term). 

These findings are what led two leading OCD and anxiety researchers to argue that within session habituation is “neither a reliable predictor of exposure therapy outcome short or long term nor tantamount to learning” (p.30).⁹

This is a snapshot of the evidence base that leads us to conclude that within-session habituation, while always appreciated, is not a requirement of successful treatment. However, if, during an ERP session, we’re not focused on habituation, what are we focused on? 

Because of so much evidence that contracted Foa and Kozak’s initial EPT, researchers began to explore alternative theories and related mechanisms which might better explain the findings that within-session habituation does not appear to relate to long-term treatment outcome. That’s what we’ll explore in part 3 of our Habituation: Always appreciated, never expected series. 

References

1. Foa, E. B., & Kozak, M. J. (1986). Emotional processing of fear: exposure to corrective information. Psychological Bulletin, 99(1), 20-35.

2. Foa, E. B., Huppert, J. D., & Cahill, S. P. (2006). Emotional processing theory: An update. In B. O. Rothbaum (Ed.), Pathological anxiety: Emotional processing in etiology and treatment (pp. 3–24). New York, NY: Guilford Press.

3. Foa, E. B., & McLean, C. P. (2016). The efficacy of exposure therapy for anxiety-related disorders and its underlying mechanisms: The case of OCD and PTSD. Annual Review of Clinical Psychology, 12(1), 1-28.

4. Hamlett, G. E., Foa, E. B., & Brown, L. A. (2023). Exposure therapy and its mechanisms. In Fear extinction: From basic neuroscience to clinical implications (pp. 273-288). Cham: Springer International Publishing.

5. Kozak, M. J., Foa, E. B., & Steketee, G. (1988). Process and outcome of exposure treatment with obsessive-compulsives: Psychophysiological indicators of emotional processing. Behavior Therapy, 19(2), 157-169.

6. Jaycox, L. H., Foa, E. B., & Morral, A. R. (1998). Influence of emotional engagement and habituation on exposure therapy for PTSD. Journal of Consulting and Clinical Psychology, 66(1), 185-192.

7. Meuret, A. E., Seidel, A., Rosenfield, B., Hofmann, S. G., & Rosenfield, D. (2012). Does fear reactivity during exposure predict panic symptom reduction?. Journal of Consulting and Clinical Psychology, 80(5), 773-785.

8. Baker, A., Mystkowski, J., Culver, N., Yi, R., Mortazavi, A., & Craske, M. G. (2010). Does habituation matter? Emotional processing theory and exposure therapy for acrophobia. Behaviour Research and Therapy, 48(11), 1139-1143.

9. Jacoby, R. J., & Abramowitz, J. S. (2016). Inhibitory learning approaches to exposure therapy: A critical review and translation to obsessive-compulsive disorder. Clinical Psychology Review, 49, 28-40.