Tri-axial recording of event-related potentials during passive cognitive tasks in patients with Alzheimer's disease

A novel dynamic mathematical microelectrode model (a model of solvent and solute kinetics in electrolyte-filled microelectrodes) was deduced from experimental observations made on standard (single-barrelled, 3.0 M KCl-filled, approximately 10 Mohm]) electrodes using (a) electrodiffusion, electro-osmosis, and continuity equations that were placed into the constraints of electrode geometry, and (b) handbook/textbook parameter values, only. The model proved to be able to faithfully reproduce all observed electrochemical and electrical electrode properties, i.e. even those that constituted no part of the model's experimental basis. In theoretical tests, the model shows, for the standard electrode that (a) inside the electrode, any profiles in electrical potential and electrolyte concentration are occurring at the most distal part (approximately 50 microm) of the tip region, (b) asymmetrical shifts in electrolyte concentration just inside the electrode tip opening are the true cause of the electrode's current rectification, and (c) strong transelectrode currents are producing water flows across the electrode orifice that may affect the volume of smaller and medium-sized cells. In further tests, the model shows, among other things, for non-standard electrodes that (a) decreasing the electrode electrolyte concentration will give rise to marked decreases in electrolyte leakage from the electrode, but only very minor changes in tip potential, and (b) increasing the surface charge of the electrode glass (increases in zeta potential) and/or decreasing the electrode electrolyte concentration will produce increases in electro-osmotic water transport, which may be desirable for the intracellular injection of water-soluble (electro-neutral) substances.