Improving Impedances

Since the impedance at the REF electrode affects signal quality for all EEG channels, we recommend starting with the REF electrode.

General

Always verify that there is good contact between electrode and scalp. Ensure all electrodes are being pulled onto the scalp by the cap and there are no creases in the cap causing electrodes to “float".

A thin, elastic cap placed over the electrode cap can further reduce impedances. It presses gently on all electrodes, particularly in occipital positions.

Ensure that you are not having Bluetooth connection problems. If you are, consider the following options:

• Remove all Bluetooth devices from your Windows computer. Don't just disconnect, remove.
• Ensure no other Bluetooth devices are in your Windows device list.
• Move the laptop closer to the Explore amplifier.
• Ensure you have not activated a Bluetooth search in Windows.
• Change room.
• Restart your laptop.
• Contact us.

Gel electrodes

1. Begin working on the reference electorode. Position the reference electrode and apply gel. Make sure the reference does not move. If it does, an adhesive, medical electrode or an ear clip electrode can be considered. To further improve impedances, gently apply a medical, abrasive scrub to the skin (Nuprep® or similar). Make sure to disinfect the skin after applying the scrub.
2. Apply conductive gel through the openings at the back of the electrodes with a blunt syringe.
3. Move the syringe in a circular motion to push hair away from the electrode. This will allow the gel to form a conductive bridge between the electrode and the scalp.
4. Apply more gel as needed. However, do avoid gel pools, as this can introduce cross-talk between channels.
5. Good gel electrode impedances are ~10 kΩ

Dry electrodes

1. Use flat electrodes for bare skin, like the mastoid and forehead. Ensure that there are no stray hairs between the electrode and skin.
2. Use brush electrodes for areas covered in hair. For thick hair, XL brush electrodes can penetrate the hair better.
3. Twist brush electrodes back and forth while gently pushing them into scalp. This allows the bristles to penetrate hair more easily. Ideally, all bristles should touch the scalp.
4. Good dry electrode impedances are less than 100kΩ for flat electrodes placed on bare skin, and less than 300kΩ for brush electrodes placed on hair. However, these impedences can be lowered using a dash of gel or paste on the REF electrode, and by applying a scrub to the skin before electrode placement (see point 1. under Gel electrodes).