1. A method for sustained neural function modification in a patient comprising: generating an amplitude modulated signal having at least one frequency component above a physiologic stimulation frequency range; and applying the amplitude modulated signal to selected neural tissue in the patient for altering a function of the tissue without heating the tissue to temperatures lethal to the tissue, wherein said amplitude modulated signal has a peak voltage, said peak voltage being sufficient to alter the function of the tissue in the patient, wherein the function remains altered for a given period of time after application of the signal to the tissue is ceased.