The research demonstrated that amplitude-modulated radio frequency (RF) fields could preferentially cause a biochemical change in isolated brain tissue depending on the specific frequency of modulation. The experiment was performed with isolated brain tissue to test whether modulated RF fields could interact with an animal via the central nervous system or whether the peripheral nervous system was needed. The experiment was motivated by the observation that the results could not easily be explained by a mechanism that involved heating of the sample. By 1980, positive results were found to be based on a true response of the samples to RF radiation. The experiments were begun to establish the electromagnetic field parameters that were critical to induce the biological changes observed. To simplify the exposure situation and analysis, the modulation frequency alone was used without the RF carrier wave.