Impedance
Electrical resistance of a recording site, typically 1-3 MΩ.
Impedance is the electrical resistance between a recording site and the surrounding tissue, measured in megohms (MΩ). It's a critical specification that affects signal quality and noise characteristics.
Why it matters: Impedance influences the signal-to-noise ratio of your recordings. Sites with appropriate impedance for your signal type will give cleaner, more reliable data.
Typical ranges:
- Low impedance (0.5-1 MΩ): Large sites, better for LFP, lower thermal noise
- Medium impedance (1-2 MΩ): Balanced for mixed recordings (spikes + LFP)
- High impedance (2-3+ MΩ): Small sites, optimized for single-unit spikes
Practical implications: Higher impedance increases thermal noise (Johnson noise) but can improve spatial selectivity for spike recordings. Your amplifier's input impedance should be at least 10× higher than site impedance.
Material factors: Impedance depends on site size and coating material. Iridium oxide coatings can lower impedance while maintaining small site dimensions.