A method for long-term artifact-free recording of single unit activity in freely moving, eating and drinking animals

A method for long-term artifact-free recording of single unit activity in freely moving, eating and drinking animals is described. A dual channel field effect transistor (FET) which functions as dual source followers is mounted directly on the head socket of the animal and the pins are connected directly to chronically implanted microwire electrodes. Unit activity inputs to the FETs from two closely spaced electrode wires, one recording and one indifferent, were differentially amplified through a circuit with high common mode rejection ratio. Use of the FETs reduced the signal source impedance of long lead wires from the electrodes to the main amplifier and differential recording from two close electrodes cancelled mastication-related myoelectric potentials as common mode signals. Both movement and chewing artifacts were completely eliminated by these techniques.