[1] Mercury swivel commutators are typically used in electrophysiological experiments on head-free[clarification needed] or moving animals.
Whereas electrical recordings from stationary, head-fixed animals can be done with electrodes attached directly with wires to the amplifier and recording setup on a stereotaxtic rig, in freely moving animals a commutator is needed to prevent twisting of the wires attaching the electrode, which moves and rotates with the animal's head (often multiple revolutions in one direction), to the amplifier/recorder, which is in a fixed position.
These traditionally use slip rings for coupling, which can introduce electrical noise into the connection[2] as the contact points slide over the surface of the slip-rings, causing microscopic bumps which result in uneven conductivity.
To reduce the electrical noise the contact points need to be pressed against the slip rings with greater force.
Slip rings are traditionally used but these can introduce electrical noise and signal degradation into temperature sensing circuit, whereas mercury swivel commutators are more reliable and accurate.