Post traumatic stress symptoms also impact the hippocampus, which is a part of the brain in the limbic system which is responsible for learning and memory formation as well as encoding and retrieving information. Exposure to traumatic experiences can lead to hyperarousal in this area of the brain. This can lead to abnormal memory processing. It can lead to repeatedly recalling certain memories, specifically nightmares, traumatic memories, and intrusive thoughts. It can also lead to an inability to recall memories or selective amnesia.