FINITE-ELEMENT ANALYSIS APPLIED TO EXTRACELLULAR MICROELECTRODE DESIGN

Whilst limited success has been achieved with the use of planar metal microelectrodes to record extracellular action potentials generated by cultured neurons, the signal-to-noise ratios obtained generally make it difficult to identify individual signals accurately. We discuss, with the use of numerical computer solutions, how the electrode design can be modified to achieve significant increases in the signal amplitudes. A variety of electrode geometries in proximity to an ideal spherical cell are modelled by computer, and the potentials at the electrodes calculated using the finite-element method (assuming a uniform transmembrane current density of 10 pA-mu-m-2). First, by comparison of the solutions for a cell completely surrounded by conducting fluid with that for a cell above an electrode mounted on a flat insulating base, we illustrate the importance of including extracellular boundaries in the model. We then consider an electrode at the base of a narrow groove cut into the insulator, with the cell confined directly above the electrode, and show how the recorded potential increases significantly with groove depth. Finally, a cell confined in a cubic pit is modelled and the electrode potential found to be greater than seven times that for a planar electrode.