Implication of output signal from Optical Topography and fMRI

Non-invasive neuroimaging techniques can be divided into the following three categories judging from the property of their measured parameters: 1) magneto-encephalography (MEG) and electroencephalography (EEG), which measure direct neural activity, 2) magnetic resonance spectroscopy (MRS) and positron emission tomography (PET), which measure metabolic activity, and 3) functional magnetic resonance imaging (fMRI) and near infrared spectroscopy (fNIRS), which measure hemodynamic responses accompanied with neural activation. When we use these techniques, we implicitly assume that there are tight coupling between those physiological parameters. However, fMRI and fNIRS inevitabiy include responses from respiratory and autonomic nerve systems as artifacts. Therefore, it is required to elucidate whether and how signals obtained by fMRI and fNIRS reflect neural activity accompanied with stimulus-induced brain activation. In this paper, we report one of experimental approaches using animal and human subjects.