An EEG system with carbon wire electrodes and an anti-polarization circuit for simultaneous EEG-fMRI recording

Background Simultaneous EEG-fMRI (Electroencephalography-functional Magnetic Resonance Imaging) recording offers high temporal resolution electrophysiological recording and high spatial resolution hemodynamic recording from the same experimental runs. Carbon wire electrodes (but not solid electrodes with carbon leads) are suitable for simultaneous EEG-fMRI recording, especially in high field MRI, because they cause less RF (Radio Frequency) heating (Bonmassar, 2004) and less susceptibility artifacts (Krakow et al., 2000) than metallic electrodes. In addition, carbon wire electrodes are comfortable to wear during long recording sessions. However, carbon wire electrodes have not been used widely in human EEG because of its relatively high impedance and the electrode polarization, or imbalance of DC potentials among electrodes. The problem associated with the high impedance is negligible, especially with EEG recorders with high input impedances. Electrode polarization causes randomly fluctuating potentials and saturation of the EEG recorder. In this study, we developed a prototype EEG system with three carbon wire electrodes and a inhouse made pre-amplifier that was equipped with an anti-polarization mechanism. The system was evaluated in an auditory ERP (event-related potential) experiment.