Instrumentation and Technique
Core concepts
Accurate NCS depends on proper electrodes (active, reference, ground), stimulator placement, and settings: sensitivity, sweep speed, filters, and stimulus intensity. The ground electrode reduces noise; active and reference electrodes are placed to capture the desired response. Supramaximal stimulation ensures all fibers are activated. Averaging improves small sensory responses.
Technique essentials
Maintain consistent inter-electrode distance, mark stimulation sites, and measure distances carefully. Use appropriate filter settings (low-frequency and high-frequency cutoffs) to reduce artifact while preserving signal. Keep the limb warm; cold increases latency and slows velocity. Check impedance and electrode contact to avoid artifact.
Traps
- Submaximal stimulation producing falsely low amplitudes.
- Inconsistent distances causing velocity errors.
- Wrong filter settings distorting the waveform.
- Poor grounding or loose electrodes creating noise and artifact.
- Forgetting temperature control.
Rule of thumb
Stimulate until the response stops growing (supramaximal), then increase slightly. If the amplitude keeps rising with intensity, you are not supramaximal and the study is unreliable.