Countless trauma survivors with posttraumatic stress disorder (PTSD) have experienced the power of cognitive-behavioral therapy (CBT) to help them get their lives back. A study that I co-authored with my colleagues at Penn suggests how this treatment helps people recover.

Prolonged exposure, a well-studied form of CBT for PTSD, often leads to the dramatic reductions in PTSD symptoms—things like nightmares, avoiding trauma-related situations, trouble sleeping, and so forth. The treatment also leads to important changes in negative thoughts that are common in PTSD—thoughts like “I am a weak person.” We wanted to know whether one of these sets of changes was driving the other: Do improvements in negative thoughts lead to improvements in PTSD symptoms? Or is the reverse true?

Participants in the study were 64 female survivors of sexual or nonsexual assault who received 10 sessions of prolonged exposure for PTSD. They reported their symptoms and their PTSD-related thoughts at each treatment visit, which allowed us to follow their progress on both of these factors across the course of treatment.

Our analyses showed that improvements in trauma-related thoughts led to changes in PTSD symptoms, whereas the reverse was not true. In other words, it seems as though CBT is effective because it leads to improvements in the kinds of thoughts a person has about the trauma and what it means, which then leads to symptom improvement.

It’s important to point out that prolonged exposure does not focus on in-depth examination of the trauma-related thoughts like other CBT therapies do (for example, cognitive processing therapy). Instead, the cognitive changes seem to be a result of the behavioral changes that people make through the treatment—for example, resuming activities that they’ve been avoiding.

The findings from this study reinforce the importance of asking about the thoughts that trauma survivors with PTSD have that might be keeping them stuck, and making sure to address them as part of the treatment.