Electrical Properties of Metal Microelectrodes

ABSTRACT. As metal microelectrode use increases, especially in intraoperative procedures, there is a need for greater understanding of the intrinsic signal and noise properties of these electrodes. In this communication we explore some intrinsic noise levels in the electrode-amplifier system and its frequency response function. Noise levels were studied in the presence of a grounded Faraday cage, an ungrounded Faraday cage, and an open electrode-amplifier system, In the 100-2000 Hz frequency range, total noise power in the grounded Faraday cage was 44 μV, compared to 168 μV for the ungrounded Faraday cage and 525 μV without any shielding. The Faraday cage appeared to reduce most of the low frequency noise and grounding reduced mostly line noise. This noise was still in the region of 1000 times greater than the noise in other electrode-amplifier systems. The frequency response of the metal microelectrode system is fairly consistent above 1000 Hz but decreases sharply below 1000 Hz, showing approximately −15 dB between 100 and 1000 Hz. Even though these measured results are fairly mediocre compared to other electrode-amplifier systems, in practice they are still acceptable because single-cell recording amplitudes (intraoperatively, with human subjects) are on the order of 100 to 10,000 times greater than other recordings such as evoked potentials and EEG.