Electroencephalography functional Magnetic Resonance Imaging Is a multimodal neuroimaging technique whereby EEGand fMRI data are recorded synchronously for the study of electrical brain activity in correlation with hemodynamic changes in brain during the electrical activity, be it normal function or associated with disorders.
The simultaneous acquisition of EEG and fMRI data of sufficient quality requires solutions to problems linked to potential health risks (due to currents induced by the MR image forming process in the circuits created by the subject and EEG recording system) and EEG and fMRI data quality. There are two degrees of integration of the data acquisition, reflecting technical limitations associated with the interference between the EEG and MR instruments. These are: interleaved acquisitions, in which each acquisition modality is interrupted in turn (periodically) to allow data of adequate quality to be recorded by the other modality; continuous acquisitions, in which both modalities are able to record data of adequate quality continuously. The latter can be achieved using real-time or post-processing EEG artifact reduction software. An addition to EEG-fMRI set up is the simultaneous and synchronized video recording without affecting the EEG and fMRI data quality.
In principle, the technique combines the EEG’s well documented ability to characterize certain brain states with high temporal resolution and to reveal pathological patterns, with fMRI’s (more recently discovered and less well understood) ability to image blood dynamics through the entire brain with high spatial resolution. Up to now, EEG-fMRI has been mainly seen as an fMRI technique in which the synchronously acquired EEG is used to characterize brain activity (‘brain state’) across time allowing to map (through statistical parametric mapping, for example) the associated hemodynamic changes.
Therefore recording EEG during fMRI acquisition allows the study of their hemodynamic correlates. The simultaneous and synchronized video recording identifies clinical seizure activity along with electrophysiological activity on EEG, which helps to investigate, correlated hemodynamic changes in brain during seizures.
The clinical value of these findings is the subject of ongoing investigations, but recent researches suggest an acceptable reliability for EEG-fMRI studies and better sensitivity in higher field scanner. Outside the field of epilepsy, EEG-fMRI has been used to study event-related (triggered by external stimuli) brain responses and provided important new insights into baseline brain activity in during resting wakefulness and sleep.
