The goal of the current project is to establish the efficacy and mechanisms of exercise-enhanced fear extinction retrieval and generalization in posttraumatic stress disorder (PTSD). Exposure therapy is the gold standard treatment for PTSD, yet is only associated with remission rates of ~55% and in clear need of improvement. Exposure therapy is hypothesized to work through mechanisms of fear extinction learning, and as such, laboratory-based fear extinction paradigms are widely used as models of exposure therapy. Recent data demonstrates that moderate-intensity aerobic exercise, delivered specifically during or after fear extinction learning, can boost the consolidation of fear extinction learning. Consistent with emerging models of exercise's pro-extinction effect, our pilot data among women with PTSD found that moderate intensity aerobic exercise delivered after fear extinction learning leads to a reduction in subsequent fear responding 24hrs later, an effect that was mediated by exercise-induced increases in peripheral brain derived neurotrophic factor (BDNF). Our pilot data using multivariate pattern analyses (MVPA) also identified divided neurocircuitry organization of fear vs safety memories, and that this divided neural organization was altered in PTSD. Building on our pilot data, the current project would 1) compare the impact of different intensities of exercise delivered following fear extinction learning on multimodal measures of fear extinction retrieval and generalization, 2) identify the impact of exercise on MVPA representations of fear vs safety memories, and 3) demonstrate that spontaneous reactivations of extinction encodings in the acute consolidation window operate as candidate mechanisms by which exercise enhances extinction retrieval and generalization. Using a 3-day fear conditioning, fear extinction, and fear extinction retrieval and recognition task during functional magnetic resonance imaging (fMRI), 200 adults with PTSD would be randomly assigned to either resting control or 30min of either light, moderate, or high intensity exercise. Testing dose-response relationships between exercise intensity and fear extinction will inform translation of this research to clinical settings. A one week-follow-up extinction retrieval test would investigate the impact of exercise on longer-term retention. This project would provide a critical evaluation of the impact of aerobic exercise on consolidation and recall of extinction learning in PTSD samples, thereby providing a strong foundation to translate this research to clinical care and enhance clinical outcomes for PTSD. The project would also provide general knowledge regarding dose-response relationships and neural mechanisms that support enhanced extinction, thereby informing development of additional novel treatments.

Inclusion Criteria:

• Age 18 - 55 years of age
• Currently experiencing at least 4 PTSD symptoms with at least 1 re-experiencing symptom (e.g., trauma memory intrusion, trauma nightmares, trauma flashbacks, intense emotional distress related to trauma, or marked physiological reactivity related to trauma) from criterion B.
• English speaking
• Medically healthy

Exclusion Criteria:

• being pregnant
• having a history of light headedness or fainting during physical activity
• having a history of chest pain during physical activity
• having a bone, joint, cardiac, or other medical condition that a doctor has said may be worsened by physical activity
• responding 'Yes' to any of the seven questions on the Physical Activity Readiness Questionnaire (PAR-Q; unless they provide a doctor's note indicating that it is safe for them to engage in aerobic exercise )
• percutaneous coronary intervention or acute myocardial infarction in the last 6 weeks
• unstable arrhythmias/implanted cardiac defibrillator shocks in the last 3 months
• Internal ferromagnetic objects (such as electronic devices, surgical implants, shrapnel, etc.)
• Nonremovable dental implants, such as braces or upper permanent retainers, as these will distort the MRI images we collect (note: filings, crowns, and silver or gold teeth are OK)
• Any other condition, medication, or implant that the investigator believes would degrade image quality or render data unusable
• psychotic disorders
• Permanent makeup or tattoos with metallic dyes,
• A self-reported history of loss of consciousness (greater than 30 minutes)
• physical disabilities that prohibit task performance (such as blindness or deafness)
• Any other condition that the investigator believes might put the participant at risk
• Claustrophobia
• History of cardiovascular disease
• on-going traumatic event exposure (e.g., living with an abusive partner)
• Severe substance use disorder.
• unstable medication (changes within the past ~4 weeks)
• Acute sedatives/pain killers (e.g., benzodiazepines, Vicodin) and prescription stimulants (e.g., Adderall) would not be permitted for 6 hours prior to the study visit.