Present and future of simultaneous EEG-fMRI.

The brain's activity can be measured in numerous complementary ways, including electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). The simultaneous acquisition of EEG and fMRI was originally developed to make the localization of the generators of often subtle pathological activity commonly observed in EEG recordings of patients with epilepsy more sensitive and spatially accurate by mapping their hemodynamic correlates. Now, the value of the information provided by simultaneous EEG-fMRI is being evaluated in a clinical context, while in parallel, more sophisticated data analysis techniques, e.g. with electrical source imaging or dynamic causal modeling, have begun to be applied to increase the technique's sensitivity and allow the study of brain network structure. Beyond its clinically oriented application in epilepsy, simultaneous EEG-fMRI recording has now gained interest as a tool for basic and systems human neuroscience, e.g. the study of neuro-vascular coupling and cognitive studies. In this review, we give an overview over the current use of simultaneous EEG-fMRI, its applications to the study of epilepsy as well as human cognition and systems neuroscience and ongoing and anticipated methodological developments.