Bernstein Center for Computational Neuroscience, Gxc3xb6ttingen, Germany. armin@nld.ds.mpg.de|Bernstein Center for Computational Neuroscience, Gxc3xb6ttingen, Germany. armin@nld.ds.mpg.de|Bernstein Center for Computational Neuroscience, Gxc3xb6ttingen, Germany. armin@nld.ds.mpg.de