Current Medical Diagnosis & Treatment in Psychiatry

Extinction & Exposure Therapy

Despite its evident clinical utility, systematic desensitization is based on an essential misperception of the laws of classical conditioning. Classical conditioning is essentially ephemeral. Organisms stop responding to the conditioned stimulus when it is no longer paired with the unconditioned stimulus. Pavlov’s dogs may have learned to salivate to the ringing of the bell, but if Pavlov kept ringing the bell after it was no longer paired with the meat powder, the dogs soon stopped salivating to its ring. This is referred to as the process of extinction, in which conditioned stimuli lose their capacity to elicit a response when they are presented too many times in the absence of the unconditioned stimulus.

This basic feature was considered so troublesome by early behaviorally oriented psychopathologists that they felt compelled to explain how such an ephemeral process could account for a long-lasting disorder such as a phobia (most phobias don’t remit spontaneously over time). O. Hobart Mowrer solved the riddle when he postulated that phobic reactions essentially involve two learning processes: classical conditioning, to instill the anxiety response to a previously neutral stimulus; and operant conditioning, to reinforce the voluntary escape or avoidance behaviors that remove the patient from the presence of the conditioned stimulus before the anxious arousal can be extinguished. In essence, people who acquire a phobic reaction to a basically benign stimulus don’t extinguish (as the laws of classical conditioning predict they should), because they don’t stay in the situation long enough for classical extinction to take place.

This conclusion led some behavior theorists to suggest that although systematic desensitization was undoubtedly effective, it was unnecessarily complex and time consuming. The essential mechanism of change, they suggested, was extinction, not counterconditioning, and the only procedure needed was to expose the patient repeatedly to the feared object or situation. Of course, the therapist would also have to do something to prevent the patient from running away or otherwise terminating contact with the feared situation. Thus, according to exposure theorists, it was not necessary to ensure that patients experienced no fear in the presence of the phobic stimulus (as Wolpe claimed). Rather, all that was required was to get them into the situation and to prevent them from leaving until the anxiety had diminished on its own.

Several decades of controlled research have suggested that the extinction theorists were correct and that exposure (plus response prevention) is at least as effective as systematic desensitization and is more rapid in its effects. That does not necessarily mean that it is more useful than systematic desensitization in practice; many patients find exposure therapy very distressing and prefer the kinder, gentler alternative provided by systematic desensitization. Although exposure typically works more rapidly than does systematic desensitization (and both work more rapidly than do other nonbehavioral alternatives), it often takes as long to persuade a patient to try exposure techniques as it does to complete a full course of systematic desensitization. Nonetheless, it is now clear that exposure (with response prevention) is a sufficient condition for symptomatic change and that Wolpe was in error when he suggested that allowing a patient to experience anxiety in the presence of the phobic situation delayed the process of change. Although patients who already have acquired a conditioned fear response will undoubtedly experience distress when exposed to the object of their fears, the fact that they become anxious during the course of that exposure neither facilitates nor retards the extinction process. (This is why most behavior therapists no longer use the term “flooding” to refer to exposure therapy; although it may be descriptive of the level of anxiety induced, it is misleading in that it seems to imply that the induction of anxiety is itself curative in some way.)

Exposure plus response prevention has a clear advantage over systematic desensitization (and virtually every other type of nonbehavioral intervention) in the treatment of more complex disorders related to anxiety. It appears to be particularly helpful in the treatment of severe obsessive-compulsive disorder (OCD) and severe agoraphobia. For example, treatment for a patient who has a fear of contamination and repetitive hand-washing rituals might involve having a therapy team spend a weekend locked in the patient’s home, having the patient intentionally contaminate his or her hands and food with dirt (by shutting off the water to prevent hand washing). Similarly, a patient with severe agoraphobia would be encouraged to visit settings that he or she typically avoids (eg, shopping malls or grocery stores) during the busiest times of the day and would be prevented (again by a therapy team or group) from leaving until his or her anxiety had subsided. Although systematic desensitization has had limited success with such severe disorders, the process of constructing and working through the literally dozens of hierarchies required typically makes the approach wildly impractical.

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