What is the 10-20 System?

The 10-20 System is an internationally recognized method for placing electrodes on the scalp during an electroencephalogram (EEG). It ensures consistent and reproducible recording of electrical brain activity by defining electrode positions relative to the size and shape of the head.

Principles of the 10-20 System

The term "10-20" refers to the proportional distances between electrode placement points:

  • 10% or 20% spacing: Electrodes are placed at intervals of 10% or 20% of the total distance between defined anatomical landmarks.
  • Anatomical landmarks: The primary reference points are:
    • The nasion (the depression between the forehead and nose)
    • The inion (the prominent bump at the back of the skull)
    • The preauricular points (just above the ear canal on both sides)

Step-by-Step Explanation of the 10-20 System

  1. Measurement: Measure the circumference of the head, and the distances between the nasion and inion, as well as between the left and right preauricular points.
  2. Define the midline: Identify the central midline by finding points such as Fpz, Cz, and Pz.
  3. Divide into 10% and 20% intervals: Divide the distances into proportional segments to position electrodes accurately.
  4. Assign labels: Each electrode position is labeled according to:
    • A letter indicating the brain region (e.g., F for Frontal, T for Temporal).
    • A number indicating the lateralization (even numbers for the right hemisphere, odd for the left).

Electrode Positions

The 10-20 System includes standardized positions such as:

  • Fp1 and Fp2: Frontal pole, left and right hemispheres.
  • Cz: Central midline.
  • O1 and O2: Occipital region, left and right hemispheres.
  • T3, T4, T5, T6: Temporal region electrodes.

Clinical Applications

The 10-20 System is widely used in various medical and research contexts, including:

  • Diagnosing epilepsy and monitoring seizure activity.
  • Studying brain function during sleep (polysomnography).
  • Investigating brain disorders such as encephalopathy or brain death.

Advanced Insights

For expert-level EEG interpretation, variations of the 10-20 System are used, such as the 10-10 and 10-5 systems, which provide higher spatial resolution by increasing the number of electrodes.

Additionally, integration with modern neuroimaging techniques like MRI and MEG allows for precise mapping of functional brain activity.