NE Tutorials

In this page we will soon provide a variety of tutorials. Enjoy and send us feedback!

EEG tutorials

How to record EEG

Please see

- | StarStim tCS EEG recording (Jove)

- | A short introduction to NIC v1.2

Referencing your EEG data

In the first place, you should place carefully the CMS and DRL electrodes. They provide a basic electrical reference to the system. These two electrodes should go over the left or right mastoid (best to always stick to one side). First clean up the mastoid area where you are going to attach the DRL/CMS electrodes (using Sticktrode adhesive electrodes). You can use a paper napkin with some water or alcohol. Removing grease and dry skin will help you get good signal. Stick the DRL/CMS electrodes close to each other, with the DRL on the bottom. These two Sticktrode electrodes should be close to each other but not touch. The CMS electrode should be on top and squarely on top of the mastoid bone. This will avoid contamination from blood vessels (ECG like signals).

For visualization, you can also choose a reference electrode in NIC: another electrode, or the average of the other used electrodes. These settings in NIC only affect visualization, not the recorded data.

Once your data is saved on a file, you can always digitally (re)-reference the data. Mathematically, this means that you will subtract the measurement of an electrode or the average of some electrodes to all the electrode set. This is very advisable, as it will remove common noise from your data.

How you precisely do this, should not be too important. Note that EEG measures voltages, and, physically, they are only defined up to a constant. In a sense, which reference you use should not be critical to your analysis.

Regarding linked-ears or linked-mastoid setups,

1- Physically linking the ears with a real cable is a dubious thing to do, as it forces the potential in one site of the scalp to be equal to that of other: this will distort the electrical potential distribution on the scalp, and its topography (the important bit). Nevertheless, this can be done digitally by re-referencing (a better approach).

2- In reality, the physics of EEG imply that only potential differences are important “real” and relevant. In a sense, referencing data to some value does not matter at all. Only the electrical potential topography is important. However, algorithms may make assumptions on the reference method.

If you need a linked-ear/linked-mastoid type of referencing, you could do: i) take the data normally electrically referenced to anywhere (e.g., the normal mastoid setup), but add an electrode to the other mastoid. ii) Then, after the data has been collected, re-reference the data digitally. iii) Use this re-referenced data in your analysis

The math of that would be to subtract from each electrode Voltage V the average of the two mastoids voltages (V1 and V2):

V --> V - (V1+V2)/2

If you place the Enobio CMS/DRL in the mastoid (e.g., Vm1), this means V1=0 and

V --> V - V2 /2

(you may also add a new channel to the data in reference to the CMS, with values V= - V2/2.)

Transcranial stimulation tutorials

Remember that also for stimulation you should place carefully the CMS and DRL electrodes. These two electrodes should go over the left or right mastoid (best to always stick to one side). First clean up the mastoid area where you are going to attach the DRL/CMS electrodes (using Sticktrode adhesive electrodes). You can use a paper napkin with some water or alcohol. Removing grease and dry skin will help you get good signal. Stick the DRL/CMS electrodes close to each other, with the DRL on the bottom. These two Sticktrode electrodes should be close to each other but not touch. The CMS electrode should be on top and squarely on top of the mastoid bone. This will avoid contamination from blood vessels (ECG like signals). CMS/DRL electrodes are used throughout the stimulation session for impedance monitoring of your setup.

- | Stimulation configuration with NIC v1.2