Long-term exposure therapy outcome in phobia and the link with behavioral and neural indices of extinction learning

Extinction learning is regarded as a core mechanism underlying exposure therapy. Under this assumption, studies have looked at the predictive value of the extinction learning paradigm for exposure therapy outcomes. However, predicting factors of long-term exposure therapy success have not been established. Participants with a specific phobia (SP) for spiders were included in a double-blind randomized controlled trial. Participants were randomly assigned to receive exposure therapy (n = 25, 24 females) or an active control intervention, progressive muscle relaxation (PMR; n = 18, 15 females). Symptom levels were measured with the Fear of Spiders questionnaire (FSQ) at baseline (T0), after the intervention (T1), and at six- (T2) and twelve (T3) months follow-up. At baseline, participants completed a three-day fMRI fear conditioning, extinction learning, and extinction recall paradigm. Indices of extinction were defined as self-reported threat expectancy and fear, and neural activation during stimulus presentations and threat omission in the ventromedial prefrontal cortex and nucleus accumbens, based on prior data. Mixed model analysis revealed that the exposure therapy group had an overall stronger decrease in phobic symptoms over time than the PMR group (β = 10.95, p < .001). However, none of the indices of extinction learning were predictive for FSQ scores after exposure therapy at the longest follow-up measurement (T3). In sum, the current results show the long-term effectiveness of a single session of exposure therapy for reducing a specific fear of spiders but no baseline characteristics were identified that predicted individual differences in exposure therapy success after one year.