I'm not 100% confident with this, as I haven't done it myself. But if you make a mouse by attaching an object like a computer chip or screw onto your hand and then apply pressure, you'll be generating electricity for the circuit board to make the pointer move.
This is probably how they used to do this at one time (using screws and whatnot) and now we're using more technologically advanced materials like Pixar goop and computer chips. The types of fibers that light upon our screens when we touch them would not transfer enough force into the material that we use to make these mouse-to-electronic pointers so there must be some type of electric current coming from somewhere acting as a power...