Signal processing aspects of simultaneously recorded EEG, pulse and fMRI

Recording of EEG during fMRI scanning is a recent technique that provides new perspectives on the underlying generators of classical EEG phenomena appearing in spontaneous brain activity, such as the alpha rhythm, interictal spikes and sleep spindles. The theoretical principle, on which the method is based, is quite simple. By making a statistical comparison between fMRI scans in which the EEG-phenomenon is present and in which it is absent, and detecting the voxels in which this difference is significant, one can localize the brain regions involved in the generation of the EEG phenomenon under study. Furthermore, one can determine whether the phenomenon corresponds to an activation or a de-activation of the brain region. In practice, however, there are many bio-signal processing problems to be solved: the artifact removal in the EEG, the demodulation of the EEG, the extraction of an EEG reference from the multi-channels, the determination of a sensible correlation co-efficient (in which heart beat effects and breathing are eliminated) and its statistical significance. In this paper, several innovations concerning the signal processing of simultaneously recorded fMRI, PULSE and fMRI are presented and applied in a case study on the generators of the alpha-rhythm.