Humans have a magnetic sensor in our eyes, but can we detect magnetic fields?

By Ed Yong | June 21, 2011 11:00 am

Many birds have a compass in their eyes. Their retinas are loaded with a protein called cryptochrome, which is sensitive to the Earth’s magnetic fields. It’s possible that the birds can literally see these fields, overlaid on top of their normal vision. This remarkable sense allows them to keep their bearings when no other landmarks are visible.

But cryptochrome isn’t unique to birds – it’s an ancient protein with versions in all branches of life. In most cases, these proteins control daily rhythms. Humans, for example, have two cryptochromes – CRY1 and CRY2 – which help to control our body clocks. But Lauren Foley from the University of Massachusetts Medical School has found that CRY2 can double as a magnetic sensor.

Foley worked with Drosophila flies, which can normally sense magnetic fields using cryptochome. You can show this by placing them in an artificial magnetic field and training them to head in a specific direction in search for food. Normal flies can do this easily. Mutants that don’t have the cry gene, which makes the cryptochrome protein, lose their ability to find their meal.

To restore their internal compass, Foley simply has to give the mutant flies extra copies of cry. But she found that the human version of the gene works just as well. When she loaded her mutants flies with human CRY2, she found that they could sense magnetic fields like their normal peers. Foley also found that human cryptochrome is sensitive to blue light. It only managed to restore the magnetic sense of flies when they were bathed in this colour.

These simple experiments show that human cryptohrome can act as a magnetic sensor. This doesn’t mean that it does, much less that humans can sense magnetic fields. Plugging human cryptochrome into an alien environment like the body of a fly tells you very little about what it does in its native surroundings.

Roswitha Wiltschko, one of the scientists who first discovered the magnetic sense of birds, says, “To sense the magnetic field, one does not only need a molecule like cryptochrome, but also an apparatus that picks up the changes in that molecule and mediates it to the brain. Drosophila obviously has this apparatus, but humans? I have my doubts.” Steven Reppert, who led the new study, is also cautious. However, he notes that Cry2 is heavily active in the human retina. “It’s beautifully poised to sense light but we don’t know if it has the downstream pathways that communicate magnetic information to the brain. The possibility exists.”

A radical idea

The connections between light, cryptochrome and a magnetic sense were laid out by Klaus Schulten and Thorsten Ritz in 2000, in a bravura paper that united biology and quantum physics. They suggested that when cryptochrome is struck by blue light, it transfers one of its electrons across to a partner molecule called FAD.  Electrons normally waltz around in pairs, but thanks to the light, cryptochrome and FAD now have lone electrons. They are known as a “radical pair”.

Electrons also have a property called “spin”. In a radical pair, the spins of the two solo electrons are linked – they can either spin together or in opposite directions. These two states have different chemical properties, the radical pair can flip between them, and the angle of the Earth’s magnetic field can influence these flips. In doing so, it can affect the outcome or the speed of chemical reactions involving the radical pair. This is one of the ways in which the Earth’s magnetic field can affect living cells. It explains why the magnetic sense of animals like birds is tied to vision – after all, cryptochrome is found in the eye, and it’s converted into a radical pair by light.

Several experiments in the past few decades have support Schulten and Ritz’s theory. Foley’s work also seems to fit – human cryptochrome can support a magnetic sense in flies, in a way that depends on blue light. But Wiltschko thinks that using the human protein is a red herring. “All cryptochromes should be light-sensitive and since they form radical pairs, they should be sensitive to magnetic fields. The authors are describing intrinsic properties of cryptochrome. Using human cryptochrome is a nice gag!”

Indeed, Reppert says, “Of all the cryptochromes one could think of, the human one seemed the most interesting. We thought that if it did work, it might reignite some interest in magnetoreception in humans, which has waned down to virtually nothing.”

Can humans sense magnetic fields?

The current consensus is that humans cannot sense magnetic fields. Birds can do it, as can bats, turtles, ants, mole rats, sharks, rays, and more. Recently, Czech scientists have suggested that foxes, cows and deer also have the same ability. But look at all the recent reviews in this field, and you’ll see very little mention of our own species. A decade ago, a German group showed that our vision is slightly more sensitive in some directions than in others, but the results have not caught on.

It wasn’t always like this. In the 1980s, Robin Baker from the University of Manchester carried out a series of experiments which seemed to show that humans could sense magnetic fields. He took busloads of blindfolded volunteers on winding journeys for several kilometres before asking them to point their way back home. They did so more often than expected, and if they wore magnets on their heads, their accuracy dropped.

The results were published in Science and you can read Baker’s own description of his study in this 1980 issue of New Scientist. He even wrote a book about it. At the time, Baker said, “Whatever the repercussions, we have no alternative but to take seriously the possibility that Man has a magnetic sense of direction.”

Unfortunately, the main repercussion was a fierce series of rebuttals. Over the next decade, several groups around the world failed to repeat Baker’s results, even though Baker himself had no problems in doing so. He argued that their failure could have been due to local magnetic anomalies or brief changes in the strength of the magnetic field due to solar activity.

An American duo – Gould and Able – charitably suggested that Baker’s British students “either had cues available to them which were absent in our experiments, or are dramatically better than Americans in using whatever cues may be involved.” Max Westby and Karen Partridge, who failed to replicate Baker’s results in Sheffield, were less kind. “Perhaps it depends on which side of the Pennine Hills the experiments are conducted?” they asked. “It is obviously extremely difficult to counter all conceivable explanations for a negative result but we are forced to wonder about the ecological importance of a magnetic sense, the existence of which is so difficult to demonstrate.”

In the end, Baker relented and he moved on to the science of sperm. When I talked to him about the new study, he confesses that he hasn’t kept up with the field. “I’d spent nearly a decade, tested thousands of people under all sorts of conditions, and had absolutely no doubt. Then people did a few tests here and there and claimed the experiments didn’t replicate,” he says. “Even after I’d collected everybody else’s results and published that taken together, they did in fact constitute successful replication, nobody wanted to know. There was an element of ‘Sod them, then’.”

Reppert thinks that Baker’s story was an unfortunate one, especially since he stopped just when others were starting to discover light-based magnetic sensors. “I think Baker’s work was very good work but a lot of people had trouble reproducing aspects of it,” says Reppert. “It’s just very hard to do these sorts of behavioural experiments in humans.”

The hardest sense

Magnetoreception has to be one of the hardest of all animal senses to study. Thorsten Ritz says, “Basic things that you do in other senses don’t make sense when it comes to magnetoreception. Almost every other sense is linked to an opening in bone structure – eyes, ears and so on. The magnetic sense could sit anywhere in the body because the magnetic field penetrates the body.”

To complicate matters, we don’t really know what a magnetic sense would be used for. For birds and turtles, it seems obvious that an internal compass would help them to navigate over long migrations. But that doesn’t really apply to humans, and we know that lost humans tend to go round in circles when other landmarks are unavailable.

But navigation isn’t the only use for a magnetic sense. Recently, John Philips has suggested that animals could use magnetic fields to estimate distances over much smaller scales. Indeed, it’s possible that foxes could use a magnetic range finder to gauge the distance of their pounces, when their prey is hidden by snow.

It’s clear that magnetic senses will remain alluring and controversial for many years to come. Baker has left the field behind, but he is still intrigued by it. “I would be really thrilled if somebody managed to vindicate those ten years of work, because I still have no doubt that there is a real phenomenon there,” he says. “This new paper is a very long way from being vindication, but just to read somebody saying that human magnetoreception deserves another look did give me a brief surge of satisfaction.”

Reference: Foley, Gegear & Reppert. 2011. Human cryptochrome exhibits light-dependent magnetosensitivity. Nature Communications

Images by JJ Harrison and Biswarup Ganguly

For more on magnetic senses, see my feature in New Scientist, and also:

tweetmeme_style = ‘compact’;


Comments (19)

  1. Kat

    Interesting… I’m wondering if (and it’s a very big if) there is some residual magnetic reception in our eyes, that might account for some unusual “ghost” sightings, which I seem to recall being attributed to magnetic fields? Probably not, but interesting to ponder

  2. Peter Ellis

    The logic simply does not follow.

    Just because cryptochromes are necessary (in some not fully understood way) for the function of the Drosophila magnetic sense, that does not mean the cryptochrome is a magnetic sensor in and of itself. In addition, the fact that the human version can substitute for the fly version does not mean it has the same function in humans.

    To see the absurdity of the logic, consider this: Drosophila flies with mutations in the scalloped gene have abnormally shaped wings. The human homologue, transcription factor TEF-1, is able to compensate for this defect and allow normal wing formation. Therefore humans may have wings.

  3. abadidea

    Ever since I was young, I’ve occasionally seen distortions in my vision that look exactly like the magnetic field you get when you pour iron filings around a bar magnet. I see very thin lines, almost transparent, emanating from a certain point. I quickly reasoned they can’t be ACTUAL magnetic fields, because I tend to see them randomly against complex backgrounds, but never around an actual magnet. I’ve always wondered what causes the distortions though, and of course this reminded me.

    I suspect it may be related to the that you see in patterned images on computer screens.

    But I always hoped against hope it may be the early signs of a magnetic superhero mutation.

  4. Gregorylent

    We can perceive energies science has no clue about. “magnetism” is a good start:-)

  5. hrm

    abadidea: does it look something like this?

    It’s probably scintillating scotoma, or another kind of aura.

    Gregorylent: evidence plz?

  6. Dave

    There’s another consideration with human subjects which doesn’t seem to be accounted for. Due to the longevity of humans, the lens in the human eye can yellow with age. This yellowing selectively absorbs blue light, the very same light that appears to affect the cryptochrome receptors. Thus, it may be worth repeating the human trials while taking the age of the subject into account, or, perhaps, even using subjects who have had cataract surgery involving the replacement of the human eye lens with an artificial implant.


    P.S. I have had cataract surgery on one eye (but not the other), due to complications from surgery for a detached retina (Look up vitrectomy, if you have a strong stomach!). I have a significant difference in the perception of colours between the two eyes now.

  7. me

    The subjects in the Baker study were blindfolded, so a yellowed lens would have no effect.

  8. As “me” pointed out, the subjects are blindfolded. This in itself is an indictment of an experiment that is designed to determine the function of a blue-light-powered protein.

    It would be interesting to see whether the original, more successful, experiments simply differed in that the blindfolds were removed at the destination before the individuals were asked to guess the direction of “home”, whereas the other experiments retained the blindfold. In the latter case, no blue light would mean no electron pairs and no magnetic sense.

    My experiment would be different; I’d use a blindfold with SMT blue LEDs inside at a low level, and I’d have swivel-chairs in the van carrying the participants so it’d be difficult for them to gauge direction by remembering motion. Alternatively, I’d find a way of numbing the inner ear, although the ensuing nausea would probably interfere, and anything that messes with nerves in the inner ear could also affect the optic nerves by locality or similarity. Upon arriving at the location, I’d give the participants a good spin in a chair just to “reset” their knowledge of direction by traditional means, then ask them to guess.

    The blue LEDs should have empowered their Cryptochromes to provide an output; that just reduces it to a question of whether or not the output can be transduced into an intelligible signal.

  9. Christopher Rucinski

    @Peter Ellis
    You have a very good point there, and the author of this post does state that humans might not have the mechanism needed to detect the changes where the Drosophila flies do. However, there seems to be some errors associated with it.

    “To see the absurdity of the logic, consider this: Drosophila flies with mutations in the scalloped gene have abnormally shaped wings. The human homologue, transcription factor TEF-1, is able to compensate for this defect and allow normal wing formation. Therefore humans may have wings.”

    You see, the Drosophila flies that have mutated scalloped genes have abnormally shaped wings – take note that they have wings. When the human gene TEF-1 is used, the Drosophila fly now has normal wing formation. The mutation of the scalloped gene did not stop the growth of the wings; it just created abnormal wings. So just cause we have the gene does not mean we “may have wings”. It just means that we can make normal wings if we had the gene that is used to make wings.

  10. Akep

    I have no doubt that we could potentially see magnetic fields.

    After several controlled, analytical sessions of psilocybin and studying the effects on myself, I became convinced of the drug turning “filters” off in the brain for the extraneous information that lies beyond the standard visible spectrum. Fractal organization of nature, be it an individual leaf, plant, field, forest, and so on became exceedingly apparent, as did the fractal structure of water, snow, and clouds. And, it all adhered to phi. Also being made visible during peaks were close-by strong magnetic fields, instantly being recognizable by field lines shaping familiar toroids.

    I believe the information is always there and that our bodies are receptive without our conscious awareness, it’s just a matter of a longstanding human lifestyle limiting information no longer necessary to our survival, and perhaps a lack of training.

  11. Dave

    Another interesting question regards screening of magnetic fields by the vehicle being used to transport the people. The steel used in automotive bodies will take and hold a magnetic field. It’s indeterminate (well, at least without testing it) as to how much magnetic screening this may produce. But, it’s an effect that needs to be logged as part of the experiment.


  12. mk

    Many people can see them. It’s called AURAs and it’s exactly the same phenomenon as aurora borealis, only in smaller scale. Everybody’s heart generates strong magnetic field that can be measured even couple of meters away from the body. When charged particles hit that field it produces color effect which can be seen. Anybody can learn it fairly quickly. The biggest obstacle is to UNEDUCATE yourself since you cannot see something you don’t believe to be possible.

  13. M.E. Sessums

    When I had an MRI for a neck injury, I was inside the magnetic torus for about 45 minutes. Bored in a dark tube, with a loud pounding noise beating weird rhythms, I closed my eyes. Moving patterns seemed to be visible when I closed my eyes. The test required several different modes of MRI sensing, and when the rhythm changed the patterns my eyes seemed to perceive also changed. I have always wondered what it was that my eyes were detecting, and have thought it must have been some magnetic phenomena.

  14. hrm

    mk, the body does not generate a significant magnetic field (if it did, compasses wouldn’t work near you, etc.) and there are no high-energy charged particles flying around at ground level to cause the kind of radiation that would look anything like an aurora. (If there were, *everyone* would see it, not just people who suffer from auras.) Auras are a purely neurological phenomenon — some kind of malfunction of the visual cortex. It’s not completely understood yet, but that’s no excuse to introduce patent nonsense and mystical mumbo-jumbo. At least not on this forum.

  15. me


    As the links in the article to Baker’s work describe, there were two groups. Both were blindfolded and driven around, and then asked to point the direction toward home. But one group had their blindfolds removed and were allowed to look around before pointing, while the other left their blindfolds on. Contrary to what Baker expected, he claimed that his *blindfolded* group was more accurate at pointing the way home than the group allowed to look around first. (?!)

    In any case, I don’t think he had any idea about a possible mechanism (involving light-activated proteins) so he didn’t think to shine blue light or otherwise in anyone’s eyes. But yes, if the claim is now that some protein complex gains a magnetic response when excited by blue light, then obviously Baker’s experiment had nothing to do with it, since his subjects’ eyes weren’t exposed to any light!

  16. abadidea

    hrm: No, it doesn’t look anywhere near that severe. I did have migraines for a few years as a child, and I think I saw spots a few times, but I don’t remember ever feeling ill when I see the distortions that resemble magnetic fields. I reckon they’re purely optical illusion arising from complex patterned backgrounds. You can see some bizarre distortions by googling “best optical illusions”.

  17. Just a note that “blindfolded” is not the same as “no blue light at all entering the eye”.

    That said, I think allowing one of the groups of volunteers to see their surroundings before asking them to point home, is a potential fatal flaw. Without having read the actual experimental protocol, it opens up the possibility that the non-magnet and presumably consistently blindfolded groups could “sense” the magnetic field purely through being less wrong than the others allowed to see environmental cues!

    If I were to perform the experiment I’d rather just put blindfolded volunteers in a swivel chair in the middle of a round room, and then study the differences in the distributions of the directions in which non-magnet and magnet groups of volunteers point. Buses and circuitous routes just add confounding variables.

  18. Australian aborigines can easily find their way around vast tracts of desert. A working magnetic sense would be evolutionarily advantageous in such an environment. I would start here with serious research.

  19. Charles


    Calcification of the pineal gland is shown to be closely related to defective sense of direction. In a tricentre prospective study of 750 patients lateral skull radiographs showed that 394 had calcified pineal glands. Sense of direction was assessed by subjective questioning and objective testing and the results noted on a scale of 0-10 (where 10 equals perfect sense of direction). The average score for the 394 patients with pineal gland calcification was 3.7 (range 0-8), whereas the 356 patients without pineal gland calcification had an average score of 7.6 (range 2-10). This difference was highly significant (p less than 0.01). A smaller parallel study in pigeons showed that pineal calcification also leads to a reduction in homing abilities.

    The findings suggested that the pineal gland plays an important part in directional sense and that damage to the gland, as indicated by calcification, causes defective sense of direction – perhaps by altering the intrinsic intracranial electromagnetic environment and thus affecting the magnetite response mechanism.


    Worth looking into?


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Not Exactly Rocket Science

Dive into the awe-inspiring, beautiful and quirky world of science news with award-winning writer Ed Yong. No previous experience required.

See More

Collapse bottom bar