The Patient Ground is essential for impedance measurements, keeping the amplifier in range during measurements, and removing noise and mains interference from the signals.
The Patient Ground is a lead that can be connected to the subject in combination with a wristband or snap-on sticker electrode. It must be connected to keep the amplifier in range and remove the noise and mains interference (50/60 Hz). Without a Patient Ground connection, signals won't be visible and impedance values cannot be measured by the amplifier.
The Patient Ground can be connected via a wristband or snap-on cable. Furthermore, it is also available in the TMSi EEG headcap and can be activated by gelling the GND electrode. This will disable the lead (wristband or snap-on electrode). In this Knowledge Base article, the different methods are described in more detail.
Placement of the Patient Ground
In impedance mode, users can measure electrode contact quality (impedance) for all channels, including the Patient Ground electrode. TMSi advises using a saline-wetted wristband or preparing the skin well for optimal contact when using a snap-on electrode as the Patient Ground. Ideally, keep the Patient Ground electrode at least ~5cm away from the measurement electrodes to minimize mains interference. Higher impedance in the Patient Ground electrode may result in increased mains interference across all measurement electrodes.