Small differences in weak electromagnetic fields disrupt magnetic compass orientation of C57 BL/6 mice (Rodentia: Muridae)

Abstract

Studies of learned magnetic compass orientation by C57 BL/6 mice were carried out to determine if responses to magnetic cues were disrupted by exposure to a very low-level (1–2 nT) 1.46 MHz radio frequency field. Findings show that exposure to the same intensity of the 1.46 MHz RF in training and testing (1.0 to 1.2 nT) had no effect on magnetic compass orientation. However, exposure to a slightly higher intensity of RF in training (1.3 to 2.1 nT) eliminated magnetic compass orientation either because the stronger intensity was above a critical threshold for disruption of the underlying magnetoreception mechanism, or because the difference in the RF intensities in training and testing resulted in qualitatively different patterns of magnetic input (‘magnetic modulation patterns’). Importantly, although similar effects of RF on magnetic compass orientation have been reported in other organisms, sensitivity to such low intensities of RF fields cannot be explained by current models of the mechanisms of magnetoreception in terrestrial organisms. Consequently, future research to determine if the findings from C57 BL/6 reported here are replicable is of the first importance.