Exposure to combined static and 60 Hz magnetic fields: failure to replicate a reported behavioral effect

Two experiments failed to confirm the Thomas, Schrot, and Liboff report that low-intensity magnetic fields disrupted the operant behavior of rats. In their experiment, food-deprived rats were trained to press a lever to obtain food pellets under a multiple fixed-ratio (FR) 30, differential reinforcement of low rate 18-24 s (DRL 18-24) schedule. After baseline training, the rats were exposed to a 30 min treatment in a different chamber prior to behavioral testing. When the treatment consisted of a horizontal 60 Hz magnetic field at 5 x 10(-5) Telsa aligned along the north-south axis combined with a static field that reduced the background to 2.61 x 10(-5) Telsa, the rate of lever pressing in the DRL component of the multiple schedule increased reliably during the immediately following test session. Changes in responding were not observed when the rats were exposed to either the static field or the 60 Hz field independently nor during sham exposures to the fields. In the present experiments, only the combined fields, i.e., those reported to be effective, were studied in rats using the same general behavioral and exposure protocol used by Thomas et al [1986a]. In experiment 1, the 2.61 x 10(-5) Telsa was achieved by reducing the vertical component of the static field. In experiment 2, both the horizontal and the vertical components were altered to match those used by Thomas et al. In both experiments additional magnetic field conditions were also studied to ensure that threshold values were exceeded and, in experiment 2, to address concerns about the role of harmonic frequencies of the 60 Hz field. The baseline performances approximated those of Thomas et al. Performances were compared between exposure, sham-exposure and control sessions. None of the exposure conditions altered any of the behavioral measures. The reasons for failing to replicate the results of Thomas et al. remain unknown.