Normally, EEG is recorded with gel based electrodes. If you use passive electrodes, the skin must be abraded to reduce the impedance. For active electrodes, you have to inject electrode gel between the electrode material and the skin.
The main disadvantages of gel based systems are:
- The long montage time
- The need to wash the user's hair after the recording
For these reasons g.tec developed an active and dry EEG electrode system (see Details here)
EEG recordings require a mechanical system that holds the electrode to the skin with a constant pressure at every possible recording location. g.tec hence developed the 2nd generation of the g.GAMMAcap, with a total of 160 positions according to an extended 10/20 system, to allow a very flexible electrode montage.
BCI and dry electrodes
For BCI experiments you normally use P300, motor imagery or steady-state visually evoked potentials (SSVEP) measured with the electroencephalogram (EEG) to control external devices.
power spectrum and
accuracies were calculated for dry and gel based electrodes to compare them.
Yes, g.SAHARA works with all g.tec biosignal amplifiers, starting from g.BSamp up to g.HIamp.
Yes, g.SAHARA also works with 3rd party amplifiers. You only need a custom made connector from the g.SAHARA to the 3rd party amplifier.
Just use a soft tissue with alcohol to gently clean the pins of the g.SAHARAelectrode.
Ag/AgCl electrodes have a better frequency characteristic which is required for DC recordings. Gold electrodes are maintenance free and are more robust.
Active electrodes have an additional ultra-low noise pre-amplifier located inside the electrode. The electrodes are made of sintered Ag/AgCl or gold. Both can be used for a broad frequency range, but Ag/AgCl electrodes can also be used for DC recordings. Gold electrodes can not be used for DC recordings because of the higher polarization of the material, but are suitable even for Evoked Potentials with a lower cut-off frequency of 0.01 Hz.
Active electrodes avoid or reduce artifacts and signal noise resulting from high impedance between the electrode and skin, such as 50/60 Hz power line coupling or artifacts caused by electrode or cable movements.
Furthermore there is little need to prepare the skin first. The active electrodes should be filled up with g.GAMMAgel.
For passive electrodes, abrasive gel is normally used to prepare the skin for low electrode impedance. Therefore, the electrode preparation time is longer than for the active electrodes.
To clean the electrodes and the cap, it is recommended to hold both electrodes and cap under warm running water. Remove the elastic straps from the cap first, since they can lose their elasticity when they are washed too often. For a better result, use a toothbrush and brush the gel off the cap and the electrodes.
To disinfect the electrodes, we recommend "Sekusept plus"(http://www.ecolab.com/). Put the electrodes for maximum 5 minutes in a 3 or 4% solution of "Sekusept plus" to disinfect. Never use an ultrasonic bath!
Afterwards, clean the electrodes again under running water and dab them with a towel. For drying, put the electrodes and the cap in a warm and dry place. It is advisable to put the cap on a head of Styrofoam or other location where it can maintain its form during drying
The elastic straps can be washed from time to time with a mild detergent by hand. Disinfect them only when necessary, since they lose their elasticity.
Disinfectants are very aggressive and can reduce the durability of the electrodes. Discoloration of plastic parts, the cabel or on the isolation material can occour, but doesn't affect the function.
The mechanical load for sintered electrodes has to be reduced to a minimum during cleaning. It is recommended to use an extra soft toothbrush, or an oral irrigator.
To check if the active electrodes work correctly, add a scope in your Simulink model and open it when the model is running, or use g.Recorder for data visualization. Clenching your teeth must now cause artifacts in all EEG channels, and blinking should produce artifacts over (at least) frontal electrode sites. Closing the eyes causes alpha activity in many brain regions. Check to confirm the LED of the g.GAMMAbox is ON; otherwise, replace the battery. Make sure that the connector cable from the g.GAMMAbox and g.USBamp is correctly connected. Make sure that the reference and ground electrodes are correctly inserted.
g.LADYbirds: These electrodes are acitve Ag/AgCl electrodes. The can be used for EEG recordings with the g.GAMMAcap. If combined with adhesive washers, they can also be used for ECG, EMG, EOG recordings. g.LADYbirds can also perform DC recordings.
g.BUTTERfly: These electrodes are active gold electrodes and are used in combination with the g.GAMMAcap for EEG recordings.