Do We Have a Magnetic Sixth Sense?
Could be hidden in our eyes…
Evidence that an increasing number of species sense the Earth’s weak magnetic field and navigate or determine migration routes accordingly has been mounting over the past decades. The existence of this “internal compass” in some other species remain at the level of observations or claims, lacking persuasive evidence. And now, a researcher from the California Institute of Technology (Caltech), backed by colleagues from other countries, has come forth with the astonishing claim that humans, too, have a magnetic sense and says he has finally proved it – after 30 years.
Weak, but still effective
Earth gets its global magnetic field from the dynamics in its liquid iron outer core which surrounds the hot solid iron core. This field, made of magnetic lines which come out of the magnetic north (geographic south)and returns from the magnetic south (geographic north), forms an invisible shell called “magnetosphere” which protects the Earth from energetic charged particles spewed by the sun. Earth’s magnetic poles are offset 10 degrees from its geographic poles on its spin axis.
The Earth’s magnetic field is weak. Measured at 25 microtesla near the equator, the value climbs to 60 microtesla at the poles of our planet. For comparison, the magnetic field formed in a magnetic resonance imaging (MRI) scanner is 100,000 times stronger than that of the Earth which is not worth mentioning beside Jupiter’s which is 20 million times stronger.
Despite the weakness of the Earth’s field, the magnetic field lines are detected by various animal species and used for orientation and mapping. Certain bacteria, bees, migratory birds and fish (e.g. salmon which, after traversing oceans return to the streams they were born, hopping over waterfalls on the way, to breed and die)and sea turtles (Caretta caretta), which likewise return to the beaches they had hatched to lay their eggs after spending their life in oceans, are known to possess this ability. In recent years slower species like lobsters, earthworms, snails, and aquatic salamanders were reported to respond to the Earth’s magnetic field. Experiments showed even certain mammals, too, had the magnetic sense. For instance, forest mice and mole rats were found to be making use of the magnetic field lines for selecting nest sites. According to some studies, cattle and deer align their bodies with magnetic field lines when browsing while others reported dogs turning to north or south before urinating or defecating.
A study published four years ago showed that specific neurons in the inner ears of pigeons were firing in line with the direction, polarization and intensity of the magnetic fields. In other experiments, birds were found to be able to identify north and south from the inclination of the magnetic field lines (horizontal at the equator, gradually vertical at higher latitudes).
Price of civilization?
At the focus of a feature article in the 24 June issue of Science, Caltech geophysicist Joe Kirschvink, says his decades-long observations and numerous experiments have shown that humans, too, possess a “magnetic sixth sense.” While some researchers suggest that we might have lost this magnetic sense in the process of civilization, Kirschvink says we might be still retaining its relics.
Before the Caltech researcher, in an experiment set up by biologist Robin Baker of the University of Manchester (U.K.) in 1980, when a group of students driven blindfolded to the countryside were asked to point to the compass direction of the imaginary “home” where they were taken on the bus, they almost always pointed to the correct bracket. But when the experiment was repeated after a bar magnet was inserted into the elastic of the blindfolds, the accuracy disappeared. The control group with brass bars in blindfolds were found to have retained the ability. In further experiments with blindfolded students led on a twisty route and students spun on a chair and asked to point to compass directions Baker also reported similar results.
To prove the existence of this magnetoreception”, Kirschvink set up a far more technical and sensitive experiment in his Caltech lab in 2014. To screen out the effects of electromagnetic waves in the environment, a “Faraday cage” in the form of a box with aluminum sides was placed at the center, around which numerous coils creating magnetic fields of varying configuration, direction and intensity were mounted. Then, participants were sat in the pitch dark room with banks of electrodes on their skulls monitoring cerebral activity. In the experiment involving the creation of a magnetic field with similar strength to that of the Earth which, then was pointed in several directions, the graph and the emission times of alpha waves reportedly showed that neurons detected the field and fired.
Both compass and map
Even if the experiment which Kirschvink detailed at an international gathering in Britain last April has truly established the magnetic effect, its nature and the cellular and neural mechanisms playing roles in the magnetoreception seen in experiments with various animals are not very clear.
There are two rival explanations about what’s providing the magnetic sense.
The first is a mineral called magnetite, the presence of which was discovered in the beaks of birds, noses of fish and even the human brain in recent years. According to Kirschvink, beyond functioning as a compass enabling accurate navigation, this mineral which is extremely sensitive to magnetic fields, also provides a mapping ability by detecting small local variations in the Earth’s magnetic field. But the existence of a specialized organ processing this sense and activating the neural system is an object of speculation. Even if such an organ exists, its whereabouts also remains a mystery. Although the discovery of cells containing magnetite in the beaks of pigeons in 2000s caused excitement to scientists, later these were found to have no relation to the nervous system, connected, instead, with the immune system.
Underlying the second explanation a protein called cryptochrome found in retinas of mammal (and by inference, human) eyes. When struck by short-wavelength (blue or green) rays, protein turns into a protein which harbors two unpaired electrons with either aligned or opposite spins called together a “radical pair.” In 2000, Illinois University researcher Klaus Schulten showed that magnetic fields could cause these electrons to go back and forth between aligned and opposite spin states to form light and dark patches in the field of view of birds. But here, too, cryptochrome could not be directly observed at work to establish whether it indeed carries out its ascribed function. Furthermore, lab experiments showed that magnetic field needed to trigger a cryptochrome sensor was far stronger than the Earth’s field.
All in all, it so seems that the fog shrouding the magnetic sense which researchers believe evolution has bestowed on species will remain in place for a while. But Kirsschvin who has focused his studies on this puzzle for 30 years, remains confident that with a new 900,000 dollar support fund he has obtained and help from a few Japanese colleagues, he’ll finally lift the veil.
- 1. “Maverick scientist thinks he has discovered a magnetic sixth sense in humans”, ScienceOnline, 24 June 2016
- 2. “What and where are the body's magnetometers?” Science, 24 June 2016