Stimulation Impedance Check
The impedance of the stimulation channels, including the return channel, can be measured by NIC2 before launching any stimulation protocol using the Impedance Check button. For each channel, the Impedance Check is computed via Ohm’s law.
NIC2 allows for two types of impedance check: with alternate current (AC) and with direct current (DC).
With the AC option, an alternating current of 300 µA amplitude and 30 Hz frequency is injected and the resulting voltage values are measured.
The DC impedance is measured using a 300 µA constant current. Both methods measure the impedance values for 5 seconds per pair of channels.
The impedance bar appears below the icons of the stimulation channels and its color depends on the obtained value:
• green [0 - 10] kΩ
• orange [10 - 15] kΩ
• red [15 - 20] kΩ
In the Liveview panes, by placing the cursor above the bar, a rectangle appears showing the actual impedance value. Those values are automatically saved on a text file too.
During a stimulation protocol, the impedance is monitored every second. At any instant, if the impedance exceeds 20 kΩ in any stimulation electrode, the stimulation protocol aborts to protect the subject from the high voltages generated.
EEG Impedance Check
Devices after October 2025 are enabled with an impedance check mechanism using the Impedance Check button.
This feature allows users to evaluate whether adequate electrical continuity has been established between the electrodes and the scalp. The impedance bar appears below the icons of the stimulation channels and its color depends on the obtained value: Impedance results are color-coded.
The ranges of acceptability depend on the electrode type that can be defined in the protocol settings
--> Gel electrodes:
• green [0 - 10] kΩ
• orange [10 - 20] kΩ
• red kΩ > 20kΩ or “Too high variability”
--> Dry electrodes:
• green [0 - 150] kΩ
• orange [150 - 500] kΩ
• red kΩ > 500kΩ or “Too high variability”
These indicators help assess connectivity status during setup and recording.
During protocol execution, impedance indicators retain their color for 5 minutes after a check; they then turn gray unless rechecked.
Impedance values of orange/red channels are shown in the head map popup, along with details of the stored impedance file.
A “Recheck Impedance” button is available after a check if poor contact is detected. þ Impedance checks can be performed before or during EEG recordings.
Impedance values are stored in the EEG data file and retrievable in offline mode.
If you would like to have an older device upgraded to enable impedance check, please contact support@neuroelectrics.com
In the Liveview panes, by placing the cursor above the bar, a rectangle appears showing the actual impedance value. Those values are automatically saved on a text file too.
If the Protocol is EEG only, there will be a very low current will be going through the CMS and the EEG electrode, then the Voltage is measured between the CMS and the electrode and the impedance is calculated with the Ohm law.
How to improve the contact impedance
There are several ways to decrease the impedance of the stimulation electrodes and improve the contact with the scalp:
(a) part the hair underneath the electrode
(b) clear the visible scalp using a cotton swab
(c) add more conductive liquid between the electrode and the scalp.