Mechanisms of Change in Cognitive Processing Therapy and Prolonged Exposure Therapy for PTSD: Preliminary Evidence for the Differential Effects of Hopelessness and Habituation

The present study examined two potential mechanisms of change, hopelessness cognitions and habituation, in a randomized controlled
trial of cognitive processing therapy (CPT) and prolonged exposure therapy (PE) for posttraumatic stress disorder (PTSD).
Participants were 171 adult women with a current primary diagnosis of sexual assault related PTSD. The potential mechanisms
were examined by evaluating the intraindividual change in hopelessness within the course of both treatments and subjective
units distress (SUDS) ratings (a proxy for habituation) within the course of PE. The effects of intraindividual change in
the proposed mechanisms were then examined on within-treatment changes in PTSD symptoms. Findings indicated that the participants
assigned to the CPT treatment had significantly greater pre-post reductions in hopelessness than those assigned to PE and
that the changes in hopelessness predicted changes in PTSD symptoms (R

²
 = .24). Intraindividual changes in SUDS ratings for participants in the PE treatment condition also predicted changes in
PTSD symptoms and did so independently of the effect of changes in hopelessness. Future research should examine these mechanisms
using more intensive methods of data collection that would permit the demonstration of temporality of change.