A method and apparatus for modifying a function of tissue can include the application of an electromagnetic signal output to tissue cells. The electromagnetic signal output can have a waveform with bursts of signal output amplitude that produces fields in the tissue during the burst on-time that can modify cell components. The on-time periods are followed by off-time periods of low signal output amplitude which produce lesser modification effects on cell components. The on-time periods have time durations that are non-predetermined and random. The rate of on-time bursts can be regular, and in one example periodic. In one example, the waveform has amplitudes during the on-time periods and durations of on-time periods that causes elevation of the temperature of tissue that exceeds the lethal temperature levels of 45 to 50° C.
