ACUTE EXPOSURE TO POWER-FREQUENCY MAGNETIC-FIELDS HAS NO EFFECT ON THE ACQUISITION OF A SPATIAL-LEARNING TASK BY ADULT MALE-MICE

A series of four experiments was performed to determine whether acute exposure to a range of 50 Hz magnetic fields had any effect on a learn ing task in adult male CDl mice. A radial-arm maze placed within the b ore of an electromagnet was used to assess spatial discrimination lear ning for food re ward. Subjects were reduced to 85% of their free-feed ing weight and were placed in the maze for up to 15 minutes each day f or 10 days. Performance of the task was measured by using maximum like lihood techniques to calculate the probability that an animal would no t reenter any given arm of the maze. Experimental subjects were expose d to a vertical, 50 Hz sinusoidal magnetic field at 5 mu T, 50 mu T, 0 .5 mT, or 5.0 mT (rms). Control subjects were exposed only to a backgr ound time-varying field of less than 50 nT and the ambient static fiel d of about 40 mu T. The variation in the applied magnetic field was le ss than 5% except at the ends of the arms, where it approached 10%. It was found that all eight groups of subjects (n = 10 in all cases) sho wed similar increases in performance with testing, and the acquisition curve for each group of experimental subjects was not significantly d ifferent from that of their control group (P > 0.05 in all cases). It was concluded that exposure had no effect on learning at any flux dens ity. This result is contrary to the findings of a number of preliminar y studies, although other studies have reported that magnetic fields d o not affect spatial learning in adult male rodents. It is possible th at differences between experimental conditions might explain some of t his apparent discrepancy. (C) 1996 Wiley-Liss, Inc.