Semo, M.; Hughes, S.; Smylie, N. J.; Patton, A. P.; Pothecary, C. A.; Tam, S. K. E.; Buckland, J.; Brown, L. A.; Reardon, P. K.; Bannerman, D. M.; Hastings, M. H.; Peirson, S. N.

Many animals use the Earth\'s magnetic field for the purposes of orientation and navigation, although the sensory mechanisms remain unclear. It has been proposed that retinal responses to light may be modulated by magnetic fields. However, to date, there is no evidence for a retinal response to magnetic fields in mammals. Here we show that magnetic fields affect expression of the neuronal activity marker c-Fos in the mouse retina in a light dependent manner. These retinal responses to magnetic fields are abolished in mice lacking the candidate magnetoreceptor cryptochrome. To characterise the signalling pathways involved, we then used RNAseq and cell-type mapping. We also show that magnetic fields increase exploratory behaviour in a visually dependent task and lengthen the period of the retinal circadian clock. Together, our data provide the first evidence for a mammalian retinal response to magnetic fields at a cellular, molecular and functional level, which may influence vision.