Humans may retain a diminished ability to see the Earth's magnetic field, claims a new American study. Experiments were carried out to investigate the function of light-sensitive proteins called cryptochromes, in the eyes of fruit flies and Monarch butterflies. These proteins were found to endow these insects with the ability to detect magnetic fields. The same protein is also present in the human eye, raising the possibility that humans may also retain this ability to some extent.
'I would be very surprised if we don't have this sense; it's used in a variety of other animals. I think that the issue is to figure out how we use it', said Professor Steven Reppert at the University of Massachusetts Medical School, who led the study.
Many animals, such as migratory birds, visually detect the Earth's magnetic field in order to orientate themselves. The light-sensitive proteins, cryptochromes, are thought to be responsible for this geomagnetic navigation. In humans, the cryptochrome gene CRY2 is strongly expressed in a region of the eye called the retina. Cryptochromes are already known to regulate the human body clock, however their role in magnetoreception is less clear.
Fruit flies also express cryptochromes and are known to be able to detect magnetic fields. This can be detected by a change in direction in response to a magnetic field. In mutant fruit flies lacking cryptochromes, their magnetoreception ability was lost. Expressing the human CRY2 gene (hCRY2) in these mutant flies rescued their ability to perceive magnetic fields, suggesting that human cryptochromes are able to function in the same capacity as fruit fly cryptochromes.
'…We do not yet know whether this capability is translated into a downstream biological response in the human retina. Nonetheless, the transgenic findings with hCRY2, together with its anatomical location in the human retina and previous work showing field effects on the visual system, suggest that a reassessment of human magnetosensivitiy may be in order', state the authors of the study.
Human magnetoreception is not a new concept and was proposed over 20 years ago by Dr Robin Baker of the University of Manchester. Dr Baker conducted studies on human volunteers but was unable to determine the mechanism behind this theory.
'I think one of the things that put people off accepting the reality of human magnetoreception 20 years ago was the lack of an obvious receptor', said Professor Reppert. 'So these new results might actually be enough to tip the balance of credibility. I shall be fascinated to see'.
This study was published in the journal Nature Communications.