1. Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-1855, USA
2. Department of Physiology and Biophysics, Neuroscience Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada
3. Unit on Biologic Computation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-1855, USA