Commutators and associated accessories are available for applications in freely-moving animals, where signal leads tend to become twisted if connected directly to a stationary ampifier input connector or jack-box.  A commutator is a simple slip-ring device, sometimes referred to as a swivel, that allows the cables connected to the animal's head to turn with respect to the amplifier input while maintaining connectivity and signal integrity.  Though it seems like a relatively simple device, a good quality commutator can be a significant investment; in applications where animals can be expected to turn more than a few times in the course of a study (especially longer studies), the extra expense of a high-quality commutator is justified.  If you are looking for a type of commutator that you do not find here, let us know.  Most likely, we will be able to source it and provide it to you as part of a fully-integrated solution.