1. Research Institute for Applied Mathematics and Cybernetics, Nizhny Novgorod, 603005, Russia
2. Neuroscience Institute and Department of Mathematics and Statistics, Georgia State University, Atlanta 30303, USA
3. Department of Computational Mathematics and Cybernetics, Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, 603950, Russia
4. Department of Mathematics, Imperial College London, SW7 2AZ, UK