The International 10/20 System of Electrode Placement

international 10 20 system electrode placement

10/20 system nomenclature

Consonant indicates brain region the electrode is sampling

  • Fp = Frontal pole
  • F = Frontal
  • T = Temporal
  • C = Central
  • P = Parietal
  • O = Occipital
  • M = Mastoid

Subscript indicates side of the brain the electrode is located

  • Even numbers = right side
  • Odd numbers = left side
  • Z = midline

(The higher the number within a lobe, the farther the electrode is located from the midline)

Skull Landmarks

skull landmarks 10 20 system1. Nasion – The bridge of the nose or lowest indentation point between nose and forehead

2. Inion – Bony ridge at the base of the back of the skull. Have patient tilt head up and down to feel it better.

3. Pre-auricular points – Indentations just above the cartilage that covers the external ear openings

4. Mastoid Process – bony area located just behind the ear. Where M1 and M2 reference electrodes are placed.

Exploring electrode sites commonly used in PSG include:

  • Central leads (Cz, C3, C4)
    • Most of sleep activity detectable with these leads
    • Referenced to mastoid electrode
  • Frontal leads (F3, F4)
  • Occipital leads (Oz, O1, O2)
    • Detect alpha rhythm which signifies quiet wakefulness
  • Mastoid leads (M1, M2)

Measurements (always measured in centimeters) (1 inch = 2.5 cm)

Nasion – Inion: Measure from Nasion to Inion.
Example 40 cm total. Follow the measurement chart using the correct percentages.
Example: starting at Nasion 10% of 40 cm = 4 cm. Count four centimeters from the Nasion and mark this point as Fp1
20% of 40 cm = 8 cm. Count up 8 centimeters from Fp1 and mark this point as Fz
Count another 8 cm from Fz (20%) and mark this point as Cz
Count another 8 cm from Cz (20%) and mark this point as Pz
Count another 8 cm from Pz (20%) and mark this point as Oz
The measurement between Oz and the Inion mark should be 10% or 4 cm.

Pre-auricular to Pre-auricular
Follow the same procedure as above making sure your tape measurer passes over the Cz point. Note the total measurement in centimeters then mark your T7, C3, Cz, C4, and T8 points according to the percentages specified on the chart.

Head Circumference
Measure around the circumference of the head from Fpz with tape measurer passing over Oz, T7, and T8. Follow percentages on chart.

F3 and F4 placement
Measure from F7 to Fz and divide this number in half, marking that point then
Measure from Fp1 to C3 and divide in half, mark that point
The point where these two cross is your F3 mark
Measure from Fz to F8, divide in half and mark then
Measure from C4 to Fp2, divide in half and mark
The point where these two cross is your F4 mark

Videos on measuring

Measuring starts at 3:50

start at 2:40