Source of nonlinearity of the BOLD response revealed by simultaneous fMRI and NIRS. - Hiroshi Toyoda; Kenichi Kashikura; Tomohisa Okada; Satoru Nakashita; Manabu Honda; Yoshiharu Yonekura; Hideo Kawaguchi; Atsushi Maki; Norihiro Sadato (NeuroImage, 2008)