Influence of a complex magnetic field application in rats upon thermal nociceptive thresholds: the importance of polarity and timing.

The application of a weak (1 microTesla) complex magnetic field pattern with a relevant electrophysiological signature produced an analgesic response in rats to thermal stimuli when the pattern was presented once every 4 sec for 30 min through iron-core solenoids. In one experiment, the burst-firing pattern was presented once every 4 s for 30 min and restricted to the positive polarity, negative polarity or a bipolar equivalent. The strongest analgesia occurred when the burst-firing pattern was presented with positive polarity or as the typical bipolar signal. Administrations of the burst-firing pattern once per week for four consecutive weeks produced analgesia that was clearly evident during the first, third, and fourth weeks but not during the second week of treatment. A telephone sensor coil (that can be readily obtained from local electronic shops) was then used instead of the solenoids along with an audio (.wav) file to generate the magnetic field; the analgesia was still apparent. However, when the magnetic pattern was generated from a compact disc source the analgesia was not evoked. The current results suggest that these fields can be generated through simple commercial devices controlled by available computer software.