StaglinCenter:EEG:ImpedanceCheck
Mirror EGI Display
Checking and lowering impedance requires a lot of back and forth between the desktop monitor and your subject in the testing suite. To make your life a little easier, plug the suite monitor DVI cable into the desktop cable, labeled Mirror EGI. This way you will be able to view the impedances of the electrode sensors as you are fixing them.
If this doesn't work immediately, check System Preferences --> Display and turn on mirroring.
Just be sure to switch back to the testing suit monitor DVI when you are done!
Checking Impedance
Once the net is plugged in and NetStation is open, check that the amp is "On" in the top right corner. You can confirm this in the Dense Waveform Display panel to see that you are receiving real-time signal.
- 1. Among the NetStation panels, find the Impedance panel, which can also be located in the Panels drop down menu.
- 2. Click Measure Impedance. (It will take about a minute to load.)
You will see some (hopefully most) electrodes green, and some electrodes red. The electrode sensors marked red need a little help to gain better connection.
Lowering Impedance
To lower impedance, we're going to add more electrolyte solution to the electrodes marked red. You will need:
- the electrolyte solution you prepared for soaking the net
- a plastic pipette (located in a box in the cabinet on the right in the testing suite)
Instructions
- 1. Noting the numbers of the red electrodes in the Impedance panel, locate these electrodes on your subject's net.
- 2. With a pipette full of electrolyte solution in hand, one by one, lift (and slighlty twist) an electrode to pipette a few drops of solution into the sponge of the electrode. Wiggle the electrode back into place through the hair for better contact with the scalp.
- We are really aiming for the sponge of the electrode to be in contact with the skin of the scalp rather than sitting on the hair. Apart from creating a better channel between the electrode and scalp via solution, this direct contact with the skin is key to gaining better connection.
- 3. Repeat this process until you are satisfied with the number of green electrodes.
- This process may take 5-10 minutes. Be mindful that as time passes, solution is absorbed into the hair, electrode sponges dry, and impedance will naturally increase. SO, do not waste a large amount of time at this stage. You want to move to your task as quickly as possible. We have one more trick to help lower impedance if the pipetting isn't doing the job.
- 4. To hold the electrodes in place and increase electrode contact with the scalp,cut two 4-6in. pieces of the tubular retainer net (which you will also find in the EEG Prep Supply box)to surround the net.
- 5. Place one band horizontally over the head like a sweat band, and the other perpendicularly under the chin and over the top of the head to cover all electrodes.