Rat hipocampal slices (0.4 mm thinck) were exposed to 50 Hz ELF (6-10 V/m peak to peak), or stimulated with steady electric fields of >1-5 V/m, in combination with a weak dose (0.1 mM) of kainate to assess potential effects on neuronal excitability. Fast brain waves (30-40 Hz), within the gamma (30-100 Hz) band are associated with higher cortical function and depend on the co-ordinated activity of large numbers of neurons these were hypothesized by the investigators to potentially be sensitive to ELF. Exposure resulted in reduction of gamma frequency power and increased power at lower frequencies. Applied AC fields of 1 V/m had no detectable effect, although 2 V/m resulted in small statistically significant reductions. Steady fields altered neuronal membrane potentials by ~0.1 mV per V/m. The authors suggest these small changes probably occur through altering the firing times of neurons that are already close to threshold. Neuronal firing was observed during the gamma oscillation entrained to the peak applied field, but only during the excitatory phase of the gamma oscillation cycle, so the oscillations tended to lock onto every second cycle of the applied field.