10-20 Electrode system in electroencephalography (EEG)

The 10-20 system is used in electroencephalography (EEG).

The 10-20 system is used in electroencephalography (EEG).

Since skull shapes and sizes are known to vary greatly from person to person, a solution had to be found that would provide comparable results.

The system itself was invented by Herbert Jasper (born 27.11.1906 in La Grande, Oregon / died 11.06.1999) and is still used today in EEG.

In order to place the electrodes in the correct position during the EEG examination, the skull bone is measured from the nasion to the inion and from the preauricular points A1 and A2 along the skull with a measuring tape.

The measured distance serves as the basis for the "calculation" of the individual electrode set points and is therefore 100%.

Important: Keep the tape measure on all the time during the marking and measuring process!

First, firmly mark the starting points Nasion, Inion and the preauricular points A1 and A2 with a skin pen mark each.

Tip: To be able to determine the preauricular points optimally, have your subject open and close his/her mouth. This enables you to feel the points at the ear entrance better.

Note: We have divided the determination of the individual electrode set points into two sections to make it clearer for you. It should be noted that the following percentages for the calculation are always based on the total distance.

Section 1 (Nasion -> Inion)

Set the first partial marker at half (50%) of the total distance using a marking pen to determine the center point Cz. Now you can determine the remaining points.

As a second step, measure 10% of the total distance from the inion towards the center of the head (Cz) to determine the point Oz. Then determine point Pz by measuring 20% from the center of the head (Cz) towards the inion. To mark point FpZ, again take 10% of the total distance, but this time from the nasion towards the center of the head. Finally, measure 20% from the center of the head in the direction of the nasion.  

Example:

Total distance (Nasion -> Inion): 38cm

1st half of the total distance(point Cz): 19cm

2. first 10% from the inion towards the center of the head(point Oz): 3.8cm

3. first 20% from the center of the head towards the inion(point Pz): 7.6cm

4. Second 10% from the nasion towards the center of the head(point FpZ): 3.8cm.

5. Second 20% from the center of the head towards the nasion(point Fz): 7.6cm.

To check, you can measure the distance between the points FpZ and Fz and between the points Oz and Pz, in our example the distances are also 7.6cm (20%).

Section 2 (preauricular points / A1 (left ear from patient's patient's view) and A2 (right ear from patient's view):

Place the measuring tape centrally and crosswise from ear to ear over the patient's head so that the measuring tape and the already marked point Cz cross each other. Here, too, you first determine half of the total distance(50%), thus creating a cross in the middle of the head at point Cz.

Next, move 10% from point A1(left ear) toward A2(right ear) to determine point T3. Once you have done this, you can mark point C3 by measuring 20% from the direction of Cz(center of the head) to point A1.

Do the same on the other side of the head. That means 10% from A2(right ear) towards A1(left ear) gives point T4 and 20% from direction Cz towards point A2 lets you mark point C4.

Example:

Total distance (A1 -> A2): 36cm

1st half of the total distance(point Cz): 18cm

2. first 10% from A1 towards A2(point T3): 3,6cm

3. first 20% from the center of the head towards A1(point C3): 7.2cm

4. second 10% from A2 towards A1(point T4): 3,6cm

5. second 20% from the center of the head towards A2(point C4): 7.2cm

To check this, you can measure the distance between points T3 and C3 and between points T4 and C4. In our example, the distances are also 7.2cm (20%).

General Information:

F, T, C, P and O stand for Frontal, Temporal, Central, Parietal and Occipital.

The small "z" (zero = zero) as e.g. in Cz denotes the zero line/center line on which the electrodes are placed.

The even numbers are on the right half of the head. As a result, the odd numbers are on the left half of the head.

If you want to get a visual impression, you can find our sample video here: