1. FIRST, Aihara Innovative Mathematical Modelling Project, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
2. Institute of Industrial Science, The University of Tokyo, Meguro, Tokyo 153-8505, Japan
3. Graduate School of Frontier Science, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan
4. RIKEN Brain Science Institute, Wako, Saitama 351-0198, Japan