International 10-20 System for Electrode Placement

Terminology and measurement guidelines for the International 10-20 system of electrode placement in EEG.

International 10-20 System

A standardized international system that uses bony landmarks to determine underlying areas of cortex, ensuring symmetrical and reproducible electrode positioning.

Recording electrodes

The International 10-20 system consists of 21 recording electrodes and one Grounding electrode.

10 and 20

The percentages of measurements used to define the placement of electrodes in the system.

Fp (Frontopolar)

The letter derivation denoting the frontopolar brain region.

F (Frontal)

The letter derivation denoting the frontal brain region.

C (Central)

The letter derivation denoting the central brain region.

P (Parietal)

The letter derivation denoting the parietal brain region.

T (Temporal)

The letter derivation denoting the temporal brain region.

O (Occipital)

The letter derivation denoting the occipital brain region.

A (Auricular)

The letter derivation denoting the auricular region.

Even number subscript

Indicates electrode positions that are to the right of the midline.

Odd number subscript

Indicates electrode positions that are to the left of the midline.

z (zero) subscript

Indicates electrode positions located on the midline.

Subscript numbers

Numbers that increase as the distance from the midline increases.

Inion

The bony prominence located just above the base of the skull used as a landmark for electrode measurement.

Nasion

The bridge of the nose or the deepest indentation of the nose used as a landmark for electrode measurement.

Preauricular points

The indentation above the tragus used as a landmark for electrode measurement.

First subset electrode positions

Positions (such as $O1$, $Oz$, $O2$, $Fp1$, $Fz$, and $Fp2$) that occur at $10\%$ from the anatomical bony landmarks.

Subsequent electrode positions

Remaining electrodes (such as $Pz$, $Cz$, $Fz$) that exist at $20\%$ increments from the initial positions.

10% Measurement Calculation

If the distance from inion to nasion is $34\,\text{cm}$, the markings for the frontal polar and occipital electrodes would be made at $3.4\,\text{cm}$ from the landmarks.

20% Measurement Calculation

If the total distance is $34\,\text{cm}$, the $20\%$ increments for subsequent electrode positions are $6.8\,\text{cm}$.