1. Division of Biology, Computation and Neural Systems Program, California Institute of Technology, Pasadena, CA 91125, USA.
2. Broad Fellows Program in Brain Circuitry, California Institute of Technology, Pasadena, CA 91125, USA.
3. Centre for Computational Neuroscience and Robotics (CCNR), School of Informatics, University of Sussex, Falmer, Brighton BN1 9QJ, UK.
4. Max Planck Institute for Brain Research, 60528 Frankfurt, Germany.