A Current-based EEG Amplifier and Validation with a Saline Phantom and an SSVEP Paradigm

Electroencephalography (EEG) measures the summed electrical activity from pyramidal cells in the brain by using noninvasive electrodes placed on the scalp. Traditional, voltage-based measurements are done with differential amplifiers. Depending on the location of the electrodes used for the differential measurement, EEG can estimate electrical activity from radially (common or average reference) or tangentially (bipolar derivation) oriented neurons. A limitation of the bipolar derivation is that when the electrodes are too close together, the conductive solution used to improve electrode-skin impedance can short-circuit the electrodes. Magnetoencephalography (MEG) also enables measurements from tangentially oriented cells without concerns about short-circuiting the electrodes. However, MEG is a more expensive, and a less available technology. Measuring from both radial and tangential cells can improve the resolution to localize the origin of brain activity; this could be extremely useful for diagnoses and treatment of several neurological disorders. The work presented here builds on previous research that aims to record the electrical activity of the tangentially oriented cells with technology like that of EEG. The design of the device presented here has been improved from previous implementations. Characterization of the electronics, and validation in a saline phantom and with a steady state visually evoked potentials paradigm is presented along with a comparison to a voltage-based (vEEG) amplifier. The current-based (cEEG) amplifier satisfies suggested parameters for EEG amplifiers, and exhibited higher sensitivity to tangential dipoles in the phantom study. It measured brain activity using the same scalp electrodes as vEEG amplifiers with comparable performance.