Discovering brain-based mechanisms and predictors of clinical outcomes of EAT for patients with PTSD

While an increasing number of treatment studies employ advanced imaging techniques to capture treatment-related brain changes, as well as to identify predictors and mechanisms of clinical outcomes, the neural effects of equine-assisted therapy (EAT)-PTSD have never been studied. Here, we report results of a study in which we aimed to employ multimodal MRI, utilizing including both structural magnetic resonance imaging (sMRI) and resting-state fMRI (rs-fMRI), to determine mechanisms and predictors of EAT-PTSD outcomes (Zhu et al., Depress Anxiety 35(10):974-984. https://doi.org/10.1002/da.22816, 2018). Nineteen veterans with PTSD completed 8 weekly group sessions of EAT and underwent multimodal MRI assessments before and after treatment. Clinical assessments were conducted at baseline, post-treatment, and at 3-month follow-up. At post-treatment, patients with PTSD showed a significant increase in the functional connectivity (FC) of caudate and a reduction in the gray matter density of the thalamus and the caudate. Notably, enhanced caudate FC was positively associated with clinical improvement seen immediately at post-treatment and at the 3-month follow-up. In addition, higher baseline caudate FC was associated with greater PTSD symptom reduction post-treatment. This first-of-its-kind study demonstrates that EAT-PTSD can affect functional and structural changes in the brains of patients with PTSD, and that EAT-PTSD may target reward circuitry responsiveness and lead to a caudate pruning effect from pre- to post-treatment.