The 10-20 System is a widely used standardized method for placing electrodes in an electroencephalography (EEG) study. Below is an overview of its key features:

Key Features

  1. Name Origin:

    Named for the division of the head into increments of 10% or 20% distances, ensuring consistency regardless of head size or shape.

  2. Electrode Labeling:
    • Letters: Indicate the brain region:
      • F: Frontal
      • T: Temporal
      • P: Parietal
      • O: Occipital
      • C: Central (unofficial but commonly used)
    • Numbers: Represent hemisphere and location:
      • Odd numbers: Left hemisphere
      • Even numbers: Right hemisphere
      • "z" (zero): Midline electrodes
    • Exception: F7 and F8 are positioned over the anterior temporal regions.
  3. Reference Points:
    • Nasion: The indentation between the eyes at the bridge of the nose.
    • Inion: The bony protrusion at the back of the head.
  4. Electrode Placement:

    The skull is divided between these reference points into 10% or 20% intervals. Placement ensures standardized electrode positioning.

  5. Additional Electrodes:
    • T1 and T2: Subtemporal electrodes for the anterolateral temporal region.
    • A1 and A2 (or M1 and M2): Placed on the auricle of the ear, used in referential montages.
  6. Alternative Systems:
    • 10-10 System: A more detailed variant with more electrodes, using 10% intervals. T1 and T2 technically belong to this system but are often incorporated into the 10-20 montages.

Note: The 10-20 system ensures that EEG studies are consistent and reproducible, allowing accurate interpretation across patients with varying head shapes and sizes.