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A frontline treatment for OCD—and many anxiety disorders—is Exposure and Response Prevention (ERP). ERP involves exposure to the feared stimuli (the exposure part of treatment) and simultaneous prevention of the ritual that is typically performed in the face of the anxiety-provoking stimuli or obsession (the response prevention part of treatment).
Several randomized controlled trials have found ERP to be as efficacious as medication and to have longer benefits than medication alone, since the effects of successful ERP treatment last beyond the treatment itself, while OCD symptoms return once the medication is stopped.
Habituation vs. Inhibitory Learning Models
There are two cognitive models that attempt to explain the mechanism by which ERP for OCD works: the habituation model and the inhibitory learning model.
In OCD, habituation refers to the diminishing of an anxious physiological and fearful emotional response to frequently repeated stimuli. In ERP, habituation is hypothesized to work by shifting the belief systems a patient has (e.g., overestimation of the risk of accidentally harming someone nearby) and reducing the link between the belief and the threat appraisal.
Emotion Processing Theory, part of a Cognitive Behavioral Therapy model, asserts that patients learn new implicit and powerful lessons when they engage in ERP treatment. One such lesson has to do with the “fight or flight” system. Patients learn during ERP that their sympathetic nervous system, responsible for the physiological part of anxiety, is unable to maintain a fight or flight response indefinitely. The habituation model of ERP suggests that after some time doing an exposure, usually at least one hour, the parasympathetic nervous system is triggered to settle down the sympathetic nervous system, regardless of the person’s cognitive interpretation of what is happening. In response to this process of achieving homeostasis in the face of a feared stimulus, the individual incorporates corrective information into his or her cognitive schemas.
In essence, habituation changes behaviors first; in turn, cognitions are modified due to the behavioral proof; and emotions change last in response to the altered cognition.
An example of this process would be a patient who is engaging in an ERP to challenge his obsessions of contamination by contracting a deadly illness. In the presence of a therapist, the patient touches sinks, communal door handles, toilet seats, and bathroom floors (exposure) and goes to eat lunch without being allowed to wash his hands (response prevention).
The patient initially experiences heightened spikes of anxiety during this process but continues to engage in the exposure despite it. While doing the bathroom exposure, the person’s physiological signs of anxiety begin to subside despite the fact that he still cognitively associates the bathroom with "dirty" and with "disease." After doing this exposure and eating lunch, the patient realizes he or she did not become deathly ill despite not being able to wash his hands after touching dirty items, so he modifies the association between bathroom and illness in his head to lessen the likelihood of threat in his cognitive schema related to bathrooms.
After repeating this exposure numerous times, the person may begin to later realize the fearful emotions previously present during bathroom time have now dissipated, and in fact, he may experience excitement instead of fear when touching bathroom items, knowing he has conquered his fear. In Emotion Processing Theory of OCD, habituation plays a strong role in the learning process, as illustrated in the example above.
Another outcome of habituation learned through ERP treatment of OCD is with regard to the stimulus itself. By repeated exposures over time, a patient will begin to learn that his appraisal of threat is erroneous and that the likelihood of his worst fear occurring is far less than previously believed.
In some cases, depending on the obsession, the feared outcome cannot be physically tested like the more concrete obsessions (e.g. the bathroom example above). Some may fear going to hell when dying and become obsessed with such an existential thought. In these cases ERP allows the patient to learn to tolerate the uncertainty surrounding the feared outcome, rather than learning the feared outcome is unlikely to occur.
In cases of habituation in which the patient does find out the feared outcome is unlikely to occur, this process is thought to be driven by extinction. In extinction, the stimuli which were once associated with anxiety and threat estimation (e.g. conditioned stimuli) no longer carry these associations because the connection is no longer enforced through rituals and avoidance. This process is an example of implicit learning because the patient is not able to simply have his therapist explain that the feared outcome is unlikely to occur and needs to experience this process firsthand through exposure and response prevention therapy.
The second cognitive model thought to underlie the mechanisms by which ERP treatment works is the inhibitory learning model. This model proposes that the fear associations between the obsession and fear response still exist and the links are not necessarily abolished, as the habituation model suggests. Rather, the inhibitory learning model of ERP suggests that exposures bring new inhibitory or safety-based associations with the previously feared stimuli.
The primary goal of this model is for patients to learn that sometimes their feared outcomes (the unconditioned stimuli in a Pavlovian model of learning) occur in the presence of their obsessions, and other times their feared outcomes do not occur, and to develop a cognitive and emotional flexibility regarding what the outcome will be in the presence of an obsession (the conditioned stimuli).
Inhibitory learning has been regarded as key to the process of extinction (Bouton, 1993). The model asserts that after extinction, the conditioned stimuli (e.g. a patient’s obsession) has two meanings: it still holds the original excitatory meaning (the conditioned stimuli paired with the unconditioned stimuli or the fear response) but it also holds a new inhibitory meaning that has been learned through ERP (the conditioned stimuli or obsession paired with a no fear response). The focus of ERP through an inhibitory learning lens then becomes more toward tolerance of distress and contact with what is occurring in the present moment, rather than waiting for the natural homeostatic process of habituation to kick in, like in the earlier model.
Strengths of the Inhibitory Learning Model of ERP
The inhibitory learning model more accurately reflects the deficits in inhibition for individuals with OCD, which modern research has shown. Many patients, particularly those who have severe or refractory OCD, experience a return of their symptoms following successful ERP treatment when the treatment is habituation-focused (Craske & Mystkowski, 2006). Researchers have hypothesized that this may stem from deficits in extinction learning and neuroscientists have shown through brain studies that individuals with severe anxiety-based disorders like OCD have deficits in their inhibitory neural regulation systems during extinction (Indovina, Robbins, Nunez-Elizalde, Dunn, & Bishop, 2011).
More specifically, what this means practically is that patients with OCD show deficits in the neural networks associated with inhibitory learning, which may be part of the reason why ERP gains are not sustained for individuals once they return to old environments. Knowing this, focusing specifically on inhibitory learning (e.g. distress tolerance, sitting with uncertainty, and focus on the present moment regardless of outcome) during ERP helps patients build the skills (e.g. and form new neural associations) needed to invest in the present moment rather than investing in the outcome (e.g. “will my feared outcome occur?”), which is usually the hyper-focus of individuals with severe OCD.
The inhibitory learning model promotes adaptiveness in clients by shifting their focus to present values and experiences rather than worrying about future-oriented possibilities that may or may not ever come to pass. Additionally, the inhibitory learning model as a mechanism by which ERP works is more empowering for clients; in an inhibitory learning model, patients have the choice to decide what to focus on in the present when they are physiologically aroused by obsessions, whereas in a habituation model patients must wait passively for habituation to occur, and they often feel as if they are still being driven by their distress, as opposed to deciding what to do and how to respond to their distress.
