50 HZ MAGNETIC-FIELD EFFECTS ON THE PERFORMANCE OF A SPATIAL-LEARNINGTASK BY MICE

Intense magnetic fields have been shown to affect memory-related behav iours of rodents. A series of experiments was performed to investigate further the effects of a 50 Hz magnetic field on the foraging behavio ur of adult, male C57BL/6J mice performing a spatial learning task in an eight-arm radial maze. Exposure to vertical, sinusoidal magnetic fi elds between 7.5 mu T and 7.5 mT for 45 min immediately before daily t esting sessions caused transient decreases in performance that depende d on the applied flux density. Exposure above a threshold of between 7 .5 and 75 mu T significantly increased the number of errors the animal s made and reduced the rate of acquisition of the task without any eff ect on overall accuracy. However, the imposition of a 45-minute delay between exposure at 0.75 mT and behavioural testing resulted in the el imination of any deficit. Similarly, exposure to fields between 7.5 mu T and 0.75 mT for 45 min each day for 4 days after training had no am nesic effects on the retention and subsequent performance of the task. Overall, these results provide additional evidence that 50 Hz magneti c fields may cause subtle changes in the processing of spacial informa tion in mice. Although these effects appear dependent on held strength , even at high Aux densities the field-induced deficits tend to be tra nsient and reversible. (C) 1998 Wiley-Liss,Inc.