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Finding Electrode Locations: Detailed Rope Method

The rope method is the easiest and most accurate way to find electrode locations. This guide walks you through making and using measurement ropes.

🧵 What You'll Need

Materials: - 2 pieces of string, ribbon, or rope (non-stretchy!) - Ruler or flexible tape measure - Marker or pen - Scissors

Length: - Rope 1 (front-back): ~45-50 cm for most adults - Rope 2 (side-side): ~40-45 cm for most adults

Tip: Make them longer than needed - you can always trim!

📏 Rope 1: Front to Back (Sagittal)

Step 1: Measure

  1. Find your nasion (bridge of nose, between eyebrows)
  2. Find your inion (bony bump at back of skull)
  3. Measure from nasion OVER the top of your head to inion
  4. Note this measurement (example: 38 cm)

Step 2: Calculate Positions

Mark these positions on your rope:

Position % from Nasion Formula
Fpz 10% Total × 0.10
Fz 30% Total × 0.30
Cz 50% Total × 0.50
Pz 70% Total × 0.70
Oz 90% Total × 0.90

Example (if total = 38 cm): - Fpz = 3.8 cm from nasion - Fz = 11.4 cm from nasion - Cz = 19 cm from nasion (halfway!) - Pz = 26.6 cm from nasion - Oz = 34.2 cm from nasion

Step 3: Mark the Rope

Using your marker: 1. Start at one end (this will be nasion) 2. Measure and mark each position 3. Tie small knots at each mark OR use marker 4. Label if helpful (Fpz, Fz, Cz, Pz, Oz)

Pro tip: Double knot at nasion end so you know which end is which!

Step 4: Use the Rope

To find Cz: 1. Place rope end (double knot) at nasion 2. Stretch rope over top of head to inion 3. 50% knot/mark = Cz (top center of head)

To find Fz, Pz, etc: - Same process, use appropriate knot/mark

This rope finds all midline sites!

📏 Rope 2: Side to Side (Coronal)

Step 1: Measure

  1. Find left preauricular notch (in front of left ear)
  2. Find right preauricular notch (in front of right ear)
  3. Measure from left notch OVER Cz to right notch
  4. Note this measurement (example: 36 cm)

Use Rope 1 to find Cz first!

Step 2: Calculate Positions

Mark these 7 positions (symmetrical):

Position Location
Left preauricular 0% (starting point)
T3 ~20% from left ear
C3 ~40% from left ear
Cz 50% (center - should match Rope 1!)
C4 ~60% from left (or 40% from right)
T4 ~80% from left (or 20% from right)
Right preauricular 100% (end point)

Example (if total = 36 cm): - T3 = 7.2 cm from left ear - C3 = 14.4 cm from left ear - Cz = 18 cm from left ear (halfway!) - C4 = 21.6 cm from left ear - T4 = 28.8 cm from left ear

Step 3: Mark the Rope

7 total knots/marks: 1. Both ends (preauricular notches) 2. T3 and T4 3. C3 and C4 4. Cz (center - verify this matches Rope 1!)

Make it symmetrical - same spacing on both sides of Cz!

Step 4: Use the Rope

To find C4: 1. Place left end at left preauricular notch 2. Stretch rope over Cz to right preauricular notch 3. The C4 knot/mark = C4 position (right side)

To find C3, T3, T4: - Same process, use appropriate knot/mark

This rope finds all lateral sites on the sensorimotor strip!

🎯 Using Your Ropes Together

Finding Corner Sites

F3 & F4 (frontal corners): 1. Use Rope 1 to find Fz 2. Use Rope 2 lateral spacing (same as C3/C4 from Cz) 3. F3 = left, F4 = right, at Fz level

P3 & P4 (parietal corners): 1. Use Rope 1 to find Pz 2. Use Rope 2 lateral spacing 3. P3 = left, P4 = right, at Pz level

The ropes create a grid - midline sites + lateral spacing = all major positions!

📸 Verifying Accuracy

After Placing Electrode with Rope

Check: 1. Does it feel right? 2. Is it symmetrical (if bilateral)? 3. Look in mirror - does it look centered/correct?

If unsure: - Take a photo - Send to Slack with: "@channel Is this C4?" - Coaches verify placement

Better to check than train on wrong spot!

💡 Pro Tips

Tip 1: Make Your Ropes Once, Use Forever

Once you make good ropes: - Keep them with your equipment - Use every session - No need to remeasure each time - Much faster than measuring fresh each session

Ropes are your cheat sheet!

Tip 2: Mark Common Sites Only

Don't need all positions marked: - Focus on sites you use often (C3, Cz, C4, Fz, Pz) - Can find others by interpolation - Simpler rope = easier to use

Tip 3: Verify with Landmarks

Double-check rope accuracy: - Cz should be at vertex (top of head) - Fz should be on forehead - C4 should be above right ear

If rope doesn't match landmarks, remeasure!

Tip 4: Color-Code or Label

Make ropes easier to use: - Different colored strings for each rope - Label knots with marker - Write on masking tape wrapped around knots - Whatever works for you!

🔢 Alternative: Direct Measurement

If You Don't Want to Make Ropes

You can measure directly each session:

For C4: 1. Find Cz (50% nasion to inion) 2. Measure ear-to-ear over Cz 3. 20% to the RIGHT of Cz = C4

For each site: - Use the percentage formulas - Measure fresh each time - Takes longer but works!

Ropes are faster once you make them!

🗺️ Full 10-20 System

All Positions (Reference)

Midline (Rope 1): - Fpz, Fz, Cz, Pz, Oz

Lateral at each level: - Frontal pole: Fp1, Fpz, Fp2 - Frontal: F7, F3, Fz, F4, F8 - Central: T3, C3, Cz, C4, T4 - Parietal: T5, P3, Pz, P4, T6 - Occipital: O1, Oz, O2

Advanced positions: - POz, PO3, PO4 (between parietal and occipital)

See: Electrode Placement Guide for each site's details

🤔 Common Questions

Do I need to make ropes?

Not required, but highly recommended!

Advantages: - Much faster setup - More consistent positioning - Less math each session - Visual aid for learning

Alternative: Measure directly each time (slower but works)

How long do ropes last?

Indefinitely if you: - Don't stretch them (use non-stretchy material) - Store them safely - Don't get them wet/dirty

Some clients use the same ropes for years!

What if my measurements seem wrong?

Common issues: - Rope stretched (use non-stretchy material) - Measured incorrectly - Head shape unusual (rare)

Solution: Remeasure, verify with landmarks, or ask coach!

Can I use a flexible tape measure instead?

Yes! Some people prefer: - Flexible sewing tape measure - Mark positions with small pieces of tape - Reusable and accurate

Ropes are just easier for most people!

The rope method makes electrode placement fast, accurate, and consistent. Invest 30 minutes making good ropes once, and you'll use them for your entire training journey! 🧵📍