1. Max Planck Institute for Mathematics in Sciences, Inselstr. 22, 04103 Leipzig, Germany
2. Bernstein Center for Computational Neuroscience, Göttingen, Am Fassberg 17, 37077 Göttingen, Germany
3. IPAB, School of Informatics, University of Edinburgh, 10 Crichton St, Edinburgh, EH8 9AB, UK