Institute of Neuroinformatics, University of Zurich and ETH Zurich, 8057 Zurich, Switzerland and Institute of Physics, University of Basel, 4056 Basel, Switzerland.|Institute of Neuroinformatics, University of Zurich and ETH Zurich, 8057 Zurich, Switzerland and Institute of Physics, University of Basel, 4056 Basel, Switzerland.|Institute of Neuroinformatics, University of Zurich and ETH Zurich, 8057 Zurich, Switzerland and Institute of Physics, University of Basel, 4056 Basel, Switzerland.