The mixed results in people may be due to the fact that virtually all past studies relied on behavioural decisions from the participants. If human beings do possess a magnetic sense, daily experience suggests that it would be very weak or deeply subconscious. Such faint impressions could easily be misinterpreted – or just plain missed – when trying to make decisions.
In some animals – such as honey bees – the geomagnetic behavioral responses are as strong as the responses to light, odor or touch. Biologists have identified strong responses in vertebrates ranging from fish, amphibians, reptiles, numerous birds and a diverse variety of mammals including whales, rodents, bats, cows, and dogs – the last of which can be trained to find a hidden bar magnet.
In all of these cases, the animals are using the geomagnetic field as components of their homing and navigation abilities, along with other cues like sight, smell, and hearing.
Skeptics dismissed early reports of these responses, largely because there didn’t seem to be a biophysical mechanism that could translate the Earth’s weak geomagnetic field into strong neural signals.
This view was dramatically changed by the discovery that living cells have the ability to build nanocrystals of the ferromagneticmineral magnetite – basically, tiny iron magnets. Biogenic crystals of magnetite were first seen in the teeth of one group of mollusks, later in bacteria, and then in a variety of other organisms ranging from protists and animals such as insects, fish and mammals, including within tissues of the human brain.
In our experimental chamber, we can move the magnetic field silently relative to the brain, but without the brain having initiated any signal to move the head.
This is comparable to situations when your head or trunk is passively rotated by somebody else, or when you’re a passenger in a vehicle which rotates. In those cases, though, your body will still register vestibular signals about its position in space, along with the magnetic field changes – in contrast, our experimental stimulation was only a magnetic field shift. When we shifted the magnetic field in the chamber, our participants did not experience any obvious feelings.
Other researchers have shown that animals’ brains filter magnetic signals, only responding to those that are environmentally relevant. It makes sense to reject any magnetic signal that is too far away from the natural values because it most likely is from a magnetic anomaly – a lighting strike, or lodestone deposit in the ground, for example. One early report on birds showed that robins stop using the geomagnetic field if the strength is more than about 25% different from what they were used to. It’s possible this tendency might be why previous researchers had trouble identifying this magnetic sense – if they cranked up the strength of the magnetic field to “help” subjects detect it, they might have instead ensured that subjects’ brains ignored it.
Moreover, our series of experiments show that the receptor mechanism – the biological magnetometer in human beings – is not electrical induction, and can tell north from south.
This latter feature rules out completely the so-called “quantum compass” or “cryptochrome” mechanism which is popular these days in the animal literature on magnetoreception.
It remains to be seen what these hidden reactions might mean for human behavioural capabilities. Do the weak and strong brain responses reflect some kind of individual differences in navigational ability? Can those with weaker brain responses benefit from some kind of training? Can those with strong brain responses be trained to actually feel the magnetic field?
Human response to Earth-strength magnetic fields might seem surprising. But given the evidence for magnetic sensation in our animal ancestors, it might be more surprising if humans had completely lost every last piece of the system. Thus far, we’ve found evidence that people have working magnetic sensors sending signals to the brain – a previously unknown sensory ability in the subconscious human mind. The full extent of our magnetic inheritance remains to be discovered.
Shinsuke Shimojo, Gertrude Baltimore Professor of Experimental Psychology, California Institute of Technology; Daw-An Wu, California Institute of Technology and Joseph Kirschvink, Nico and Marilyn Van Wingen Professor of Geobiology, California Institute of Technology.