1 Center for Information and Neural Networks (CiNet), National Institute of Information and Communications Technology (NICT), 2A6 1-4 Yamadaoka, Suita, Osaka 565-0871, Japan; Graduate School of Medicine and Graduate School of Frontier Biosciences, Osaka University, 2-15 Yamadaoka, Suita, Osaka 565-0871, Japan. Electronic address: eiichi.naito@nict.go.jp.
2 Research into Artifacts, Center for Engineering (RACE), The University of Tokyo, 5-1-5 Kashiwa, Chiba 277-8568, Japan. Electronic address: ota@race.u-tokyo.ac.jp.
3 Department of Physiology, Kinki University Faculty of Medicine, 377-2 Ohno-Higashi, Osaka-Sayama 589-8511, Japan. Electronic address: akiviola@med.kindai.ac.jp.