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 repor t 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, di fferential reinforcement of low rate 18-24 s (DRL 18-24) schedule. Aft er baseline training, the rats were exposed to a 30 min treatment in a different chamber prior to behavioral testing. When the treatment con sisted of a horizontal 60 Hz magnetic field at 5 x 10(-5) Telsa aligne d 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 t he 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 reporte d to be effective, were studied in rats using the same general behavio ral 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 compo nent 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 st udied 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 co ntrol sessions. None of the exposure conditions altered any of the beh avioral measures. The reasons for failing to replicate the results of Thomas et al. remain unknown. (C) 1996 Wiley-Liss, Inc.