Visual system

Abstract

Combining both EEG and fMRI is still a challenging task. A large number of studies on the feasibility of EEG-fMRI for the visual system have been performed because it is an accessible and well-described system. A general question when performing EEG-fMRI experiments is whether typical neural patterns of the visual system as measured by EEG, such as alpha rhythm or visual evoked potentials (VEPs), are modified by the strong static magnetic field inside the MR environment. Despite two studies reporting changed evoked potentials during exposure to the strong magnetic field of the MR environment (Bunkrad et al. 1989; Sammer et al. 2005), most other studies have reported typical evoked potentials (EPs) within the magnetic field, although without systematic comparison to non-MR EPs. Typical configurations have been shown for VEPs (Bonmassar et al. 1999; Kruggel et al. 2000; Muri et al. 1998; Negishi et al. 2004; Comi et al. 2005; Becker et al. 2005, see also Fig. 1) and for visual oddball P300 potentials (Otzenberger et al. 2005; Negishi et al. 2004). The recording of VEPs at high MR B 0 fields (4.7 T) was demonstrated for monkeys (Schmid et al. 2006). EEG source localisation was also shown to be feasible for EEG data from inside the MR tomograph by Bonmassar et al. (2001) and Im et al. (2006). Depending on whether EPs were recorded in an interleaved manner (i.e. during nonacquisition intervals of the MR sequence) or continuously, the data had to be corrected for either the ballistocardiogram (BCG) or for both BCG and MR imaging artefacts. © Springer-Verlag Berlin Heidelberg 2010.