1. Cellular and Systems Neurobiology Section, Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4455;
2. Blanchette Rockefeller Neurosciences Institute, Rockville, Maryland 20850-3332; and
3. Laboratory for Neuroengineering, Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, Georgia 30332