Neurovascular diseases, such as stroke and Alzheimer’s disease (AD), have become a serious social issue these days. In this regard, it has become increasingly important to measure both neuronal activity and cortical hemodynamics. Among a variety of noninvasive neuronal imaging techniques for the human brain, both electroencephalography (EEG) and magnetoencephalography (MEG)1 can directly measure neuronal activity with time resolution below one millisecond. EEG is obviously the simplest and the most convenient neuronal imaging technique; however, its spatial resolution is low in principle owing to the inhomogeneous electrical conductivity in the human head, which consists of different kinds of tissues, such as, brain, blood vessel, cerebrospinal fluid, skull, scalp, and hair. On the other hand, MEG is better than EEG in terms of spatial resolution because of the homogeneous magnetic permeability in the human head. Moreover, MEG allows noncontact measurement, while EEG requires electrodes attached to the scalp.