Referencing with the Digital Lynx SX and Cheetah 5.6.3+ 

Referencing Flexibility is of key importance when recording extracellular single units and/or LFP/EEG in chronically implanted animals. The software-controlled analog reference selection of the Digital Lynx SX system allows use of multiple references and post-implant reference selection and optimization. This is not possible on systems with a single fixed reference, such as Intan-based headstages.  

Flexible Referencing of the Digital Lynx SX System  

Our Digital Lynx SX with the Digital Reference Selector (DRS-36) Board or Combo Board offers many options for referencing. Each DRS-36/Combo Board allows 8 different references to be active at one time for the associated 32 input channels and also provides the option to drive 8 shared global references across all input boards. Reference options include system ground, animal ground, multiple dedicated references and any recording input channel.  

Skull Screw Ground Implant during Surgery

A Skull Screw must always be implanted on every subject. The skull screw wire is connected to one of the dedicated ground pinholes on the Neuralynx Electrode Interface Boards (EIB). This connects the animal’s body to the acquisition system ground – and MUST be made to keep the subject and recording electrodes at the same voltage potential as the system.  

System Ground (PGnd) and Animal Ground (AGnd) as Starting References  

System ground (PGnd) is often a good first choice as a reference for a newly implanted animal before all recording electrodes and references are driven to their “normal” depth. This gives a good initial indication of electrode signals and location.  

Using the system ground (PGnd) may not be the best noise reduction reference because any noise signal present on the tether ground wire will result in a common mode noise signal on all channels. This ground wire noise signal is the result of coupled external noise sources plus the voltage drop of the headstage pre-amplifier power supply differential current (~20 amp between +/- 5V amplifier power lines) times the resistance of the ground wire (<10 ohms). It is possible to see a noise voltage of 10 to 80 micro-volts between the system ground and the animal’s EIB ground.  

Animal Ground (AGnd) Reference Tether Wire Signal  

Most Neuralynx tethers and headstages have a separate “non current carrying ground wire” called Animal Ground (AGnd). AGnd is connected to the headstage ground (and thus the EIB and animal’s skull screw) and a high impedance buffer amplifier on the DRS-36 to eliminate any current flow in the wire (< 1nA). Since virtually no current flows through this wire, there is no voltage drop and is therefore an accurate representation of the true voltage potential of the subject’s skull screw for improved signal referencing purposes.  

Caution – Device for investigational use in laboratory animals or other tests that do not involve human subjects.