The International 10-20 System is a standardized method for placing electrodes on the scalp in electroencephalography (EEG). This system ensures consistent, reproducible, and anatomically correlated electrode placement for capturing brain activity. Below is a comprehensive guide to understanding and implementing the 10-20 System.

1. Overview of the 10-20 System

The name "10-20 System" refers to the distances between adjacent electrodes, which are either 10% or 20% of the total front-to-back or side-to-side scalp measurement. This system provides a systematic and comprehensive coverage of the brain's cortical areas.

2. Preparatory Steps

  1. Patient Preparation:
    • Explain the procedure to the patient and obtain consent.
    • Ensure the scalp is clean and free of oils or hair products.
    • Measure head circumference to determine electrode placement.
  2. Materials Required:
    • EEG electrodes (disposable or reusable).
    • Measuring tape, skin preparation gel, and conductive paste.
    • EEG cap (optional) for consistent placement.

3. Measurement Landmarks

To begin electrode placement, identify the following anatomical landmarks:

  • Nasion: The indentation between the forehead and nose.
  • Inion: The prominent bump on the back of the skull.
  • Preauricular Points: The depressions just above the ear canals on both sides of the head.

Note: Accurate identification of these landmarks is crucial for reliable electrode placement.

4. Electrode Placement

Electrodes are placed according to specific percentages of the measured distances between the landmarks:

  1. Measure the Head:
    • Measure the total distance from the nasion to the inion (front-to-back).
    • Measure the total distance between the preauricular points (left-to-right).
    • Measure the circumference of the head.
  2. Mark Electrode Positions:
    • Use the measurements to divide the scalp into 10% or 20% increments.
    • Mark positions using a skin-safe marker.
  3. Electrode Labels: Standard electrode names indicate brain regions:
    • Fp: Frontal pole
    • F: Frontal lobe
    • T: Temporal lobe
    • C: Central region
    • P: Parietal lobe
    • O: Occipital lobe

5. Electrode Placement Diagram

The placement of electrodes follows a symmetrical pattern. Below is an illustrative representation of the 10-20 system:

  • Midline electrodes: Fpz, Fz, Cz, Pz, Oz
  • Left hemisphere: Fp1, F3, C3, P3, O1
  • Right hemisphere: Fp2, F4, C4, P4, O2

6. Practical Tips

  • Ensure symmetrical placement to avoid errors in EEG recordings.
  • Verify electrode impedance is below 5 kΩ for optimal signal quality.
  • Regularly check for artifacts caused by poor contact or external interference.

7. Applications of the 10-20 System

The 10-20 System is widely used in clinical and research settings, including:

  • Diagnosis of epilepsy and seizure disorders.
  • Monitoring brain activity during sleep studies.
  • Assessment of brain function during neurosurgical procedures.

8. Advanced Insights

For high-resolution EEG, expanded systems such as the 10-10 or 10-5 systems are used to provide additional electrode positions and finer spatial resolution.