RSA Biofeedback Condition. The biofeedback will consist of 10 weekly sessions of training, at the same time of day for each subject. The details of the procedure for RSA biofeedback are described in Appendix A. One single practitioner, a certified biofeedback technician, will provide the biofeedback following the aforementioned protocol. In each session, 20 minutes of biofeedback will be delivered using a J&J C-2+ Physiograph. The participant will be taught to breathe at her resonant frequency, as a first step to training the individual how to produce maximal increases in amplitude of RSA. During the first session, we will measure heart rate oscillation amplitudes while the individual breathes for intervals of two minutes each at specific frequencies, ranging between 4 and 7 breaths per minute, respectively 4, 4.5, 5, 5.5, 6, 6.5, and 7 breaths per minute. We will provide a "pacing stimulus" for this purpose: a light display that moves up and down on the computer screen at the target respiratory rate. The participant will be instructed to breathe at the rate of that stimulus. We will consider the frequency yielding the highest frequency peak on the moving Fourier analysis data collected and displayed by the C-2 physiograph to be the resonant frequency. In subsequent sessions, the individual will be given biofeedback for 20 minutes. The participant will be instructed to practice breathing at her own resonant frequency for 20-minute periods twice daily for the next week. Throughout training the individual will be cautioned to breathe shallowly and naturally, in order to avoid hyperventilation.