Pretraining exposure to physiologically patterned electromagnetic stimulation attenuates fear-conditioned analgesia

The effect of weak electromagnetic stimulation on the emergence of conditioned analgesia was examined in the adult rat. Subjects were conditioned to associate a continuous 20 kHz ultrasonic tone (CS) with 0.2 mA footshock (UCS-) over five successive days. For 30 min either before or after conditioning sessions, rats were exposed to sham or pulsed (primed burst potentiation) magnetic fields (500 nT). At the end of the conditioning phase, all animals were evaluated for anticipatory analgesia following CS presentation using a hotplate analgesiometer. Data analysis suggested a statistically significant attenuation of fear-conditioned analgesia in rats exposed to electromagnetic stimulation prior to conditioning, whereas post-conditioning exposure potentiated the reduction in pain sensitivity compared to baseline measures. The present results suggest that the emergence of fear-conditioned responses is sensitive to whole body exposure to a magnetic field pattern that has been shown to induce long-term potentiation in hippocampal slices.