Mounting g.GAMMAcap

Note: In our Video section you will find a video tutorial which shows the correct montage of the g.GAMMAcap

In order to properly mount the g.GAMMAcap, -measure the distance between the nasion and inion, as well as the distance between the left and right preauricular points of the subject. The electrode in the vertex position, CZ, should be at the midpoint of these two distances. Put on g.GAMMAcap and align this measured position with the position Cz of the electrode cap. Now the electrode cap is in the correct position.

Note:  Any kind of electrode cap with predefined positions might cause some difference between the “true” 10-20 positions and the positions indicated on the cap. The amount of the deviation depends on cap size, head size and head shape. Always use the electrode position “Cz” to position the cap on the subject’s head, since this helps ensure proper placement.

Fix the cap with the chest belt and the adjustable straps to keep the cap in place.

Skin preparation and application of electrode gel

Passive electrodes

For passive electrodes (g.LADYbird, passive) preparation of the skin is required to obtain low impedance between the electrode and the skin. Use g.tec’s abrasive electrode gel for this purpose. Put a small amount of abrasive gel on the tip of a cotton bud and insert it through the hole in the electrode. Then rub the skin by moving the cotton bud to the left and to the right with slight pressure against the skin for about 10 seconds. This procedure should never cause pain! You should ask the subject if you are rubbing the skin too hard. While the top priority is avoiding pain, it is also important to rub the skin thoroughly enough to get a geed connection. Avoid rotary movements. Make sure that the gel has contacted an area of about 1 cm² of the skin.

Then insert g.GAMMAgel or abrasive gel with a syringe (without needle) or with the doser can into the electrode. Make sure that the entire electrode is filled with gel.

Check the impedances of all electrodes against the ground electrode using g.Zcheck or use the integrated impedance check when using g.USBamp. Assure perfect skin preparation for the ground electrode to obtain reliable impedance values. The impedances should be below 5 kOhm. If the impedance of an electrode is above 10 kOhm, clean the skin again.

Tip:  If g.LADYbird electrodes are used with adhesive washers directly on the skin (e.g. for EOG derivation or as mastoid electrode), the best procedure is as follows: First, attach the adhesive washer at the appropriate position, but leave the outside protection film on. Prepare the skin with abrasive gel and then remove the protection film to attach the electrode. Now fill the electrode as described above.

Active electrodes

When using g.LADYbird active or g.BUTTERfly electrodes, skin preparation with abrasive gel is not required. However, a perfect contact between the gel and an area of 0.5 – 1 cm² of skin has to be assured for proper signal quality. g.GAMMAgel is best to be applied with the genuine doser can or with a syringe (without needle). Insert the tip of the doser or syringe into the ready-mounted electrode and make sure to reach the skin. Press the can (or syringe) and move around a bit with the tip on the skin with slight pressure to make sure that gel is distributed on the skin. Then carefully fill the electrode with gel. It is essential that gel fills the gap between the skin and the electrode surface! However, using too much gel may cause shortcuts between electrodes, which ruins the signal quality.

g.LADYbird active electrodes can be used with adhesive washers directly on the skin as well (e.g. for EOG or mastoid reference derivation). In this case, just mount the electrode and fill it as described above.

g.GAMMAearclip electrodes are attached with g.GAMMAgel as well. Just put a small amount of gel onto the electrode surface (Au or Ag/AgCl disk) and put the earclip to the earlobe with the electrode outside.

Note:  Impedance checking is neither required nor possible with active electrodes! Visual inspection is the best way to enusre signal quality.

In case a signal shows high noise, drift or other disturbance, check the proper filling of the electrode ring and confirm that the gel reaches the skin. Be aware of the fact that the ground electrode is a passive electrode, and therefore it is the only electrode that needs to be mounted with special care. A very high impedance at the ground electrode may reduce the signal quality. One can use abrasive gel to prepare the skin at the ground electrode if necessary.

Using g.SAHARAsys dry electrode system

Note: In our Video section you will find a video tutorial which shows how to use the g.SAHARAsys.