Clinical Guide
10-20 Electrode Placement System.
The international standard for consistent EEG electrode placement. This system ensures reproducible recording over time and across different practitioners.
Nomenclature
Letters (Regions)
- Fp - Frontopolar
- F - Frontal
- C - Central (No specific lobe, sulcus)
- P - Parietal
- O - Occipital
- T - Temporal
Numbers (Hemispheres)
- Even numbers (2, 4, 6) - Right hemisphere
- Odd numbers (1, 3, 5) - Left hemisphere
- z (zero) - Midline (Cz, Fz, Pz)
Key Measurement Landmarks
Accurate placement begins by measuring the head using four fundamental landmarks. Ensure measurements are precise to the millimeter using a flexible metric tape measure.
| Landmark | Definition |
|---|---|
| Nasion | The bridge of the nose, directly between the eyes. |
| Inion | The bony prominence at the lower back of the skull (external occipital protuberance). |
| Pre-auricular points | The depressions slightly above and in front of the ear canal opening. |
The "10-20" Rule
The system is named 10-20 because actual electrode distances are 10% or 20% of the total distance between the primary landmarks (Nasion to Inion, and left pre-auricular to right pre-auricular). For example, Fz is placed 20% of the total Nasion-Inion distance posterior to Fpz (which is 10% above the nasion).
Common Pitfalls
- Assuming symmetry: Never assume the head is perfectly symmetrical. Always measure both sides independently.
- Hair interference: Failing to part the hair down to the scalp will artificially inflate impedance readings.
- Misidentifying the Inion: The inion can be subtle. Palpate firmly to find the true bony ridge, not just the muscle attachments.