1. A method, comprising: applying a first electrical signal to a nerve to evoke an action potential, said nerve thereafter entering a refractory period in which said nerve is refractory to further induction of action potentials; and after applying said first electrical signal, altering said refractory period by applying a second electrical signal to said nerve during said refractory period, wherein said second electrical signal is effective to alter said refractory period and is unable to stimulate said nerve to evoke an action potential.