The goal of this clinical trial is to learn if non-invasive neurostimulation of memory-related brain areas works to treat intrusive memory symptoms in adults patients with posttraumatic stress disorder (PTSD). It will also learn about the effect of this neuromodulation procedure on reorganization of memory-related brain networks. The main questions it aims to answer are: Does neuromodulation lower the number of times and the emotional severity participants intrusive memories? Does neuromodulation reduces the overall severity of PTSD? Researchers will compare neuromodulation targeting the hippocampus (a memory-related brain structure) to a control stimulation in an area not related to memory processes to see if hippocampus neuromodulation works to treat intrusive trauma memories and PTSD. Participants will: 1. Undergo magnetic resonance imaging (MRI) scans before and after neuromodulation to: a) determine a personalized neuromodulation target; and b) to measure changes in brain function from before to after treatment. 2. Receive hippocampus neuromodulation or a control neuromodulation once a week for 5 weeks. Keep a daily diary of their symptoms and the number of times they experience intrusive trauma memories.