1. Cellular and Systems Neurobiology Section, Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health;
2. Mathematical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland;
3. Center for Neural Science and Courant Institute of Mathematical Sciences, New York University, New York City, New York 10013