EEG Electrode Placement: The 10-20 System Explained for Technicians
Good EEG starts with correct electrode placement. The international 10-20 system gives every technician a standard method, so recordings can be compared across labs and over time.
The landmarks
- Nasion. The depression between the forehead and the nose.
- Inion. The bony prominence at the back of the head.
- Preauricular points. Just in front of each ear.
Measuring step by step
- Measure nasion to inion along the midline. Mark Fpz at 10% from the nasion and Oz at 10% from the inion. Mark Fz, Cz and Pz at 20% intervals between them.
- Measure from left to right preauricular points through Cz. Mark T3 (T7) and T4 (T8) at 10% from each end, and C3 and C4 at 20% further in.
- Measure the head circumference through Fpz, T3, Oz and T4. Place Fp1, Fp2, F7, F8, T5 (P7), T6 (P8), O1 and O2 at 10% and 20% intervals around it.
- Place F3, F4, P3 and P4 midway between neighbouring points.
Naming conventions
- Letters: Fp frontopolar, F frontal, C central, T temporal, P parietal, O occipital.
- Numbers: odd = left, even = right.
- z = midline (zero).
- Newer nomenclature renames T3/T4/T5/T6 as T7/T8/P7/P8.
Skin preparation and impedance
- Clean the scalp, part the hair and gently abrade with prep gel.
- Apply conductive paste and the electrode, or fill cap electrodes with gel.
- Aim for impedance below about 5 kΩ and keep values similar across electrodes. Most modern systems, such as our 24 channel EEG, show real-time impedance on screen.
Common mistakes
- Estimating positions instead of measuring, which leads to asymmetric montages.
- Using the wrong cap size.
- Leaving gel bridges between neighbouring electrodes, which shorts them.
- Not rechecking impedance after the patient moves.
Extra electrodes
Add ECG and EOG, and sometimes EMG or respiration, as polygraphic channels. A 24 or 32 channel amplifier gives room for these. See 24 vs 32 vs 64 channel EEG.
RS Enterprises includes technician training with every EEG installation. Contact us to arrange training for your team.
24 Channel EEG Machine
Ultra-portable 24 channel EEG for ICU, bedside and clinic use. ₹1.1 lakh – ₹1.35 lakh
Frequently Asked Questions
How many electrodes are in the 10-20 system?
19 scalp electrodes plus reference/ground electrodes (often A1/A2 on the ears).
What does Fp, F, C, T, P, O mean?
Frontopolar, frontal, central, temporal, parietal and occipital regions.
Can I use an electrode cap instead of measuring?
Yes, caps speed up placement, but choose the correct size and check positions.
This article is for general information for healthcare buyers and professionals and is not medical advice. Clinical decisions should be made by qualified practitioners.
