What is electrode impedance EEG?

In the context of EEG recordings, impedance is typically measured by passing a small 10-Hz current between two or more electrodes and measuring the opposition to the flow of this current (for more details, see Chapter 3 in Luck, 2005).

What causes high impedance EEG?

If all of the values are showing a high impedance, then there could be artifact or interference present. It is also possible that the connection of the ground electrode needs to be improved. Squeeze the ground electrode to the scalp/ear and observe if this improves the impedance values.

What is electrode skin impedance?

It is believed that the electrical impedance at the skin-electrode interface affects the quality of EEG signal. In most cases, a specific amplifier characterized with extremely high input impedance is required for dry electrodes. Thus this electrode can be applied to or removed from the scalp very quickly.

How is impedance of an electrode measured?

The common method for measuring the electrode-tissue impedance consists of injecting a known AC current14 (usually a square wave) and measuring the differential voltage between the electrodes6,15; this methodology is applied to measure bio-impedance in general.

What is tissue impedance?

The impedances of fat and muscle tissues are similar to previous results. Nerve tissue is shown to have higher impedance compared to muscle and lower impedance compared to fat tissue. The nerve tissue impedance peaks to just over 4 kΩ for both setups.

How do skin electrodes work?

The body contains fluids with ions that allow for electric conduction. This makes it possible to use electrodes on the surface of the skin to detect electrical activity in and around the heart and use an electrocardiograph to record the activity.

How much input-impedance needed to improve EEG data quality?

In EGI’s published paper “Scalp electrode impedance, infection risk and EEG data quality”, it is shown that when the amplifier’s “input-impedance is high enough (200 MΩ), there is negligible signal attenuation when using electrodes without abrasion.”

What is the input-impedance of an EGI amplifier?

The entire family of EGI ampliers are high-input impedance amplifiers. In EGI’s published paper “Scalp electrode impedance, infection risk and EEG data quality”, it is shown that when the amplifier’s “input-impedance is high enough (200 MΩ), there is negligible signal attenuation when using electrodes without abrasion.”

Do electrode impedances affect noise in EEG recordings?

In addition, high electrode impedances produced an increase in the noise level of the EEG, which was confined primarily to relatively low frequencies (< 5 Hz).

What is the input impedance of a modern EEG amplifier?

Modern EEG amplifiers have input impedances consisting of a resistive component on the order of 200 M Ω in parallel with a capacitive component on the order of 10 pF (corresponding to a reactance of 265 M Ω at 60 Hz). These impedances are very large compared to the scalp-electrode impedance even without scalp abrasion.