Study population: Patients and healthy adult volunteers may be studied under this protocol. Patients must have a clinical indication for the diagnostic test. Most patients will be enrolled in a primary NIH protocol, and this protocol will serve as a secondary protocol. Occasionally, patients will be enrolled in this protocol as a primary protocol when they are referred from hospitals that participate in the NINDS fellowship training program. Healthy adults will be studied by fellows-in-training to practice a new testing procedure or to provide normative data when required by changes in instrumentation or laboratory technique.