Evaluation of commercially available electrodes and gels for recording of slow EEG potentials

Objective: To test the applicability of different types of commercially available electrodes and electrode gels or pastes for recording of slow EEG potentials. Methods: Experiments were carried out on six types of reusable electrodes (silver, tin and gold cup electrodes, sintered silver-silver chloride (Ag vertical bar AgCl), platinum, stainless steel), six disposable Ag vertical bar AgCl electrode models, and nine gels or pastes. We studied the parameters, which are critical in slow-potential recording, such as polarization, initial and long-term stability and low-frequency noise. Results: The best results were obtained with the reusable sintered Ag vertical bar AgCl electrodes. The six disposable Ag vertical bar AgCl electrode models also proved to have appropriate electrical properties. Other types of reusable electrodes suffered from diverse degrees of polarization, baseline drift, low-frequency noise, high resistance, and changes in properties due to wear and tear. Seven out of nine gels or pastes contained a significant amount of chloride, which is a prerequisite for DC stability of Ag vertical bar AgCl electrodes, whereas the absolute concentration of chloride had little effect. Conclusions: Direct current (DC) coupled recording of EEG is critically dependent on the choice of electrode and gel. Significance: Our results provide rigorous criteria for choosing DC-stable electrodes and gels for DC-coupled or long time-constant AC-coupled recordings of slow EEG potentials. (c) 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.