The investigators are trying to understand if there is a relationship between the experience of traumatic events such as those experienced by people with post traumatic stress disorder and reactivity to startling noises or mild threats. So, the investigators are looking at startle reflex, heart rate, and stress hormone responses to short noises and small shocks in people exposed to trauma and who either do or do not have PTSD. Additionally, the investigators will be looking at how the menstrual cycle impacts these processes. The investigators know that women have twice the risk for developing PTSD and some research suggests that stress hormones change during the menstrual cycle and may have an effect on risk.
