Impedance Optimization

This tutorial provides a comprehensive guide to optimizing electrode impedance for Instinct headsets, helping you achieve the best possible EEG signal quality.

Prerequisites

Before you begin, make sure you have:

• An Instinct headset properly positioned on the subject's head
• The Systems Engine running and connected to the headset
• Completed the basic Headset Setup
• Conductive gel/solution for electrode contact
• Understanding of target impedance values for your application

Understanding Impedance Values

Electrode impedance directly affects EEG signal quality:

Impedance Level	Range	Signal Quality	Applications
Excellent	< 5 kΩ	Highest quality, minimal noise	Research-grade studies, BCI
Good	5-10 kΩ	Very good quality	Clinical, research
Acceptable	10-20 kΩ	Usable for most applications	General purpose
Poor	20-50 kΩ	Increased noise, usable with care	Basic monitoring, non-critical
Very Poor	> 50 kΩ	Noisy, potentially unusable	Not recommended

Step 1: Begin Impedance Checking

Start by initiating an impedance check:

curl -X POST http://localhost:42069/electrodes/impedance/start \
  -H "Content-Type: application/json" \
  -d '{
    "continuous": true,
    "channels": "all",
    "updateInterval": 1000
  }'

Expected response:

{
  "success": true,
  "status": "running",
  "sessionId": "imp-check-789012",
  "mode": "continuous"
}

Step 2: Analyze Initial Impedance Values

Retrieve the current impedance values:

curl -X GET http://localhost:42069/electrodes/impedance

Example response showing impedance values in kilohms (kΩ):

{
  "timestamp": 1620000000000,
  "values": {
    "Fp1": 25.3,
    "Fp2": 18.7,
    "F7": 32.1,
    "F3": 15.4,
    "Fz": 12.5,
    "F4": 14.2,
    "F8": 28.6,
    "T3": 35.2,
    "C3": 17.8,
    "Cz": 8.9,
    "C4": 16.3,
    "T4": 30.5,
    "T5": 42.1,
    "P3": 22.7,
    "Pz": 18.2,
    "P4": 24.5,
    "T6": 38.4,
    "O1": 27.9,
    "O2": 26.3
  },
  "status": "running",
  "sessionId": "imp-check-789012"
}

Step 3: Identify Problem Electrodes

Categorize electrodes based on impedance levels:

1. Prioritize electrodes critical to your application
2. Focus on electrodes with the highest impedance values
3. Identify patterns (e.g., all frontal electrodes have high impedance)

Step 4: Apply the Optimization Strategy

Choose your optimization approach:

Automatic Optimization

Use the Systems Engine's automatic optimization feature:

curl -X POST http://localhost:42069/electrodes/impedance/optimize \
  -H "Content-Type: application/json" \
  -d '{
    "channels": ["Fp1", "Fp2", "F7", "T3", "T5", "T6"],
    "targetImpedance": 10.0,
    "maxAttempts": 3,
    "strategy": "gentle"
  }'

This will:

• Automatically adjust electrode positions
• Apply appropriate pressure
• Make multiple attempts to achieve target impedance

Manual Optimization

For manual electrode-by-electrode optimization:

1. Apply additional gel to specific electrodes:

curl -X POST http://localhost:42069/electrodes/prepare \
  -H "Content-Type: application/json" \
  -d '{
    "electrodes": ["Fp1", "Fp2"],
    "action": "apply_gel",
    "amount": "moderate"
  }'

2. Adjust electrode position manually:

curl -X POST http://localhost:42069/motors/control \
  -H "Content-Type: application/json" \
  -d '{
    "motor": "motor-fp1",
    "action": "move",
    "parameters": {
      "position": 7.5,
      "speed": "slow"
    }
  }'

3. Adjust electrode pressure:

curl -X POST http://localhost:42069/motors/apply-pressure \
  -H "Content-Type: application/json" \
  -d '{
    "profile": "gentle",
    "electrodes": ["Fp1", "Fp2"],
    "customization": {
      "Fp1": {
        "pressure": 5.0
      }
    }
  }'

Step 5: Monitor Improvement

After each optimization step, check the impedance values:

curl -X GET http://localhost:42069/electrodes/impedance

Continue optimization until you reach your target impedance values for all electrodes.

Step 6: Use Visual Feedback

Enable LED visual feedback to aid in optimization:

curl -X POST http://localhost:42069/leds/impedance-visualization \
  -H "Content-Type: application/json" \
  -d '{
    "enabled": true,
    "colorScheme": "standard",
    "updateInterval": 500,
    "thresholds": {
      "excellent": 5,
      "good": 10,
      "acceptable": 20,
      "poor": 50
    }
  }'

This will light up the LEDs next to each electrode with a color indicating the impedance level:

• Green: Excellent
• Blue: Good
• Yellow: Acceptable
• Orange: Poor
• Red: Very Poor

Step 7: Advanced Techniques for Difficult Electrodes

For persistently high impedance:

Skin Preparation

Request skin preparation guidance:

curl -X GET http://localhost:42069/electrodes/preparation-guidance \
  -H "Content-Type: application/json" \
  -d '{
    "electrodes": ["T5", "T6"],
    "currentImpedance": {
      "T5": 42.1,
      "T6": 38.4
    }
  }'

Follow the returned guidance, which may include:

• Gently brushing hair aside
• Using alcohol wipes to remove oils
• Applying light abrasion with specialized tools
• Using skin preparation gels

Electrode Replacement

If a specific electrode consistently shows high impedance:

curl -X POST http://localhost:42069/electrodes/diagnose \
  -H "Content-Type: application/json" \
  -d '{
    "electrode": "T5",
    "diagnosticLevel": "comprehensive"
  }'

If the diagnostic indicates an electrode issue, follow the replacement guidance.

Step 8: Create an Impedance Map

Generate a visual map of impedance distribution:

curl -X GET "http://localhost:42069/electrodes/impedance/map?format=png&colorScheme=standard" --output impedance-map.png

This will provide a topographic representation of impedance across the scalp.

Step 9: Document Baseline Impedance

Once you're satisfied with the impedance values, record them as a baseline:

curl -X POST http://localhost:42069/electrodes/impedance/snapshot \
  -H "Content-Type: application/json" \
  -d '{
    "name": "baseline-session-001",
    "notes": "Initial optimized impedance values for subject 001"
  }'

Step 10: Stop Impedance Checking

When you've completed optimization:

curl -X POST http://localhost:42069/electrodes/impedance/stop

Optimization Strategies by Region

Different scalp regions often require different approaches:

Frontal Electrodes (Fp1, Fp2, F7, F3, Fz, F4, F8)

• Challenge: Oils from the forehead, limited hair
• Approach: Gentle skin preparation, moderate gel, careful pressure

Temporal Electrodes (T3, T4, T5, T6)

• Challenge: Hair coverage, curved surface
• Approach: Extra gel, position electrodes perpendicular to skin

Central Electrodes (C3, Cz, C4)

• Challenge: Thick hair, movement sensitivity
• Approach: Part hair carefully, ensure stable positioning

Parietal/Occipital Electrodes (P3, Pz, P4, O1, O2)

• Challenge: Dense hair, bony structure
• Approach: More gel, increased pressure (within comfort)

Optimizing for Specific Applications

For Research-Grade Recordings

Target impedance < 5 kΩ for all electrodes:

curl -X POST http://localhost:42069/electrodes/impedance/optimize \
  -H "Content-Type: application/json" \
  -d '{
    "channels": "all",
    "targetImpedance": 5.0,
    "maxAttempts": 5,
    "strategy": "research"
  }'

For Clinical Applications

Target impedance < 10 kΩ with focus on relevant electrodes:

curl -X POST http://localhost:42069/electrodes/impedance/optimize \
  -H "Content-Type: application/json" \
  -d '{
    "channels": ["F7", "F8", "T3", "T4", "T5", "T6"],
    "targetImpedance": 10.0,
    "maxAttempts": 3,
    "strategy": "clinical"
  }'

For BCI Applications

Target impedance < 5 kΩ with priority on specific regions:

curl -X POST http://localhost:42069/electrodes/impedance/optimize \
  -H "Content-Type: application/json" \
  -d '{
    "channels": "all",
    "priorityChannels": ["C3", "Cz", "C4", "P3", "Pz", "P4"],
    "targetImpedance": 5.0,
    "maxAttempts": 4,
    "strategy": "bci"
  }'

Maintenance During Long Sessions

For extended recording sessions, set up periodic impedance monitoring:

curl -X POST http://localhost:42069/electrodes/impedance/schedule \
  -H "Content-Type: application/json" \
  -d '{
    "interval": 15,
    "unit": "minutes",
    "duration": 30,
    "action": "notify",
    "thresholdIncrease": 10
  }'

This will notify you if any electrode impedance increases by more than 10 kΩ during the session.

Best Practices

• Start with clean electrodes and fresh gel
• Be gentle - excessive pressure can cause discomfort
• Work systematically - optimize one region at a time
• Document impedance values for research reproducibility
• Set realistic targets based on your application requirements
• Balance time and quality - pursuing perfect impedance may not be worth the time
• Consider subject comfort throughout the process

Troubleshooting

Impedance Won't Decrease

• Try a different gel application technique
• Consider if the electrode itself may be damaged
• Check if hair is blocking contact
• Verify system ground electrode has good contact

Fluctuating Impedance Values

• Check for loose connections
• Ensure subject is sitting still
• Verify environmental electrical noise is minimized
• Consider using a faraday cage for sensitive applications

Unable to Achieve Target Impedance

• Reassess if your targets are realistic
• Consider if the recording can proceed with slightly higher impedance
• Try different electrode types if available
• Document the issue for consideration during analysis

Next Steps

• Proceed to EEG Acquisition
• Explore the Electrodes API