The past decade has witnessed significant progresses in both fundamental and technical aspects related to these questions. Most of them are still under active research or remain poorly understood. In this review, we start with an overview of the physiological origins of EEG/MEG and fMRI, as well as their fundamental biophysics and imaging principles; it is followed by a review of major progresses in understanding and modeling the neurovascular coupling, methodologies for the fMRI-EEG/MEG integration and EEG-fMRI simultaneous recording; finally, important remaining issues and perspectives are summarized. Although some of the points we make in this review might be speculative or even controversial, we hope they serve to identify important scientific elements that would help to stimulate future discussion and research.
