Commutator
A commutator is a rotating electrical joint in the tether between the headstage and the data acquisition system, so that the cable above it turns with a freely moving animal and the cable below it does not.
Without one, torque accumulates in the cable as the animal turns: the animal changes its behavior to avoid the pull, the connector at the head takes the load, or the recording picks up the movement.
Two models are in the catalog, in the X-Series platform with XDAQ and the X-Series headstages. The Standard commutator is mechanical: an off-center tether attachment converts the animal's rotation into the torque that turns the rotor, with no power or sensing, so the animal supplies the force. The Commutator PRO has a low-noise motor with continuous active torque compensation, sensing rotation from a gyro on the animal side or a Hall encoder on the rotor, so the animal supplies no force; it is the choice for a mouse, or for any study in which the pull of the tether is itself a variable. Both pass the headstage's digital data stream to XDAQ, so the channel count per cable is a property of the commutator model rather than of the headstage. A commutator is optional: a head-fixed or short-session preparation connects the headstage to the DAQ directly. The two models are compared under Commutators.
Typical values
| Standard | mechanical, no power; 256 channels per cable on record headstages, 32 on stim-record |
|---|---|
| PRO | motorized, active torque compensation, gyro or Hall sensing; 256 record / 64 stim-record channels per cable; up to 4 Neuropixels ports, 9 GPIO |
| Needed when | the animal moves freely over a session |