Example of Reference Lead

Purpose of the Reference Lead

The purpose of the reference lead is to subtract any common signal between the two or three 'signal' lead pairs from those signals. Therefore, the output from the 'signal' leads is the difference between its own signal and the reference lead signal. The paired leads for each channel monitor the potential between the two endpoints. Moving one signal lead to the reference lead site would alter the channel's output.

Newer DSI implant models have the reference lead internalized and connected to the negative lead of channel 1. Legacy implants have included an additional “reference” electrode as a separate of the implant. The reference electrode serves the purpose of minimizing cross-talk between differential channels.

Placement of the Reference Lead

It is generally recommended that the reference electrode be placed near the electrode pair that has the lowest amplitude signal.  

1. • If EEG & EMG are placed, then typically near one of the EEG leads with the lowest amplitudes.
   • If ECG and EMG are placed, then typically near the EMG leads
   • If possible reduce the distance between the reference lead and the midpoint of a pair; but not in between 2 pairs.  

With all this being said, the emphasis should be more on ensuring proper surgical placement.  Therefore, the easiest way to surgically place the reference lead should have the highest priority.