1. Department of Information Engineering, University of Padova, via Gradenigo, 6/B I-35131 Padova, Italy.
2. Gatsby Computational Neuroscience Unit, University College London, London W1T 4JG, UK.
3. Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA.
4. Computational and Biological Learning Lab, Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK.