Each non-invasive neuroimaging technique has its own inherent limitations resulting from temporal and spatial inaccuracies due to the nature of information that can be measured. Recent advances in non-invasive brain imaging techniques enable us to choose a set of the most appropriate imaging modalities depending on the purpose of the study from several possible candidates. In this paper, I briefly summarize the characteristics of the major brain imaging techniques, namely, electroencephalography (EEG), magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS). Also, some examples of using these neuroimaging techniques to visualize brain activities related to subjective sensation of mental fatigue are presented to show potential application of the techniques for the quantitative evaluation of stress and fatigue.
