Our previous research of bioeffects of extremely high power pulses (EHPP) in excitable tissues (isolated brain and heart slices) did not reveal any specific effects of this radiation modality. In this study, we explored if EHPP may cause different effects when they are applied in synchronism with membrane excitation events. The experiments were performed in rat hippocampal slices. Excitatory postsynaptic potentials (EPSPs) in CA1 field were evoked by twin pulse stimulation of Schaffer collateral (20 ms interpulse interval, 1 pair/15 sec) and recorded extracellularly with a glass micropipette (2-8 Mohm).