1. Failure to meet standard MRI inclusion criteria: those who endorse claustrophobia, those who have cardiac pacemakers, neural pacemakers, surgical clips in the brain or blood vessels, surgically implanted metal plates, screws or pins, cochlear implants, implanted uterine devices, metal braces, or other metal objects in their body, especially in the eye. Dental fillings do not present a problem. Plastic or removable dental appliances do not require exclusion. History of significant injury or surgery to the brain or spinal cord that would impair interpretation of results. Pregnancy, determined by pregnancy tests on females.