The temporal sequence of change in PTSD symptoms and hypothesized mediators in Cognitive Processing Therapy and Written Exposure Therapy for PTSD.

We examined whether extinction or changes negative trauma-related beliefs occur either prior to or concurrently with changes in posttraumatic stress symptoms among individuals who received either Cognitive Processing Therapy (CPT) or Written Exposure Therapy (WET) using statistical methods that permit proper discernment of temporal sequence. Community participants with PTSD (N = 126) were evenly randomized to 12 sessions of CPT or 5 sessions of WET. We assessed within- and between-session changes in arousal and valence and changes in trauma-related beliefs 6-, 12-, 24-, 36- and 60-weeks following the first treatment session. Between-session change in post-session emotional valence temporally preceded PTSD symptom reduction among participants who received WET but did not predict subsequent symptom reduction. Although negative trauma-related beliefs changed in parallel with and correlated with PTSD symptom reduction in both conditions, this change did not temporally precede symptom reduction. Our results are inconsistent with those from prior studies and suggest these constructs may more appropriately be characterized as correlates, rather than mediators, of symptom reduction. These results highlight the value of discernment of the temporal sequence of change between hypothesized mediators and symptoms and underscore that we still have much to learn about how evidence-based treatments reduce PTSD symptoms.