Methylenedioxymethamphetamine (MDMA)-assisted psychotherapy is an experimental treatment for anxiety disorders, and initial findings suggest that it holds promise for treatment of PTSD. This study will examine brain activity in participants enrolled in an investigation of the safety and efficacy of MDMA-assisted psychotherapy in people with anxiety stemming from diagnosis with a life-threatening illness to see whether MDMA-assisted psychotherapy alters emotional reactivity to anxiety-provoking material, including positive and negative images. The study will also examine brain activity related to the experience of self-compassion/empathy in response to personalized audio scripts, and whether that response is altered by MDMA-assisted psychotherapy. Brain imaging may offer a measure of neural markers of anxiety and self-compassion that do not rely on self-report.