Science

Evidence of a “sixth magnetic sense” found in humans

A multidisciplinary team of geoscientists and neurobiologists from the Caltech Institute in California and the University of Tokyo have just published an article in the journal eNeuro in which they claim to have found evidence of a “sixth magnetic sense” in human beings. According to Joseph Kirschvink, Shin Shimojo and their colleagues, in effect, the human brain is capable of responding unconsciously to the subtle changes that occur in the Earth’s magnetic field.

The study, which can be consulted in BioRxiv, puts back on the table an area of research that had been “asleep” for decades.

We know that many animals, including migratory birds and sea turtles, have an acute “geomagnetic sense” that allows them to orient themselves in the air or ocean on journeys of many thousands of km to return, with extraordinary precision, to their nesting or nesting sites. And it has also been demonstrated that other living beings, from bacteria to molluscs, arthropods, fish or various groups of vertebrates, also possess an organ sensitive to magnetic changes. However, although magnetoreception has been well studied in all these animals, scientists have not yet been able to determine whether humans also share this extraordinary capacity.

For a good part of the 20th century, most researchers placed the magnetoreception in the same drawer in which radiesthesia or telepathy are found. That is, in the rugged and controversial terrain of the para-scientific. It was not until it was shown that many animals were capable of perceiving the magnetic field (the carrier pigeons were the first) that the magnetoreception, together with the possibility that humans also possess this “sixth sense”, began to be taken seriously.

A built-in compass
When the evidence became overwhelming, many took refuge in the idea that “carrying a built-in compass” might be acceptable for some migratory animals, though in no case for all other living things. But over the years researchers have discovered that less “traveling” animals, such as worms, snails, frogs or newts, also have this enigmatic meaning. Even many mammals seem to be able to respond to the Earth’s magnetic field. Experiments with mice and moles showed, for example, that they used magnetic field lines to locate their burrows. Even cattle or deer line up their bodies with the orientation of those lines when they graze. And dogs “look” north or south (the dominant lines of the Earth’s magnetic field) when they urinate or defecate.

But what about humans? Kirschvink and the rest of the authors of this study set out to address this old question using the most modern encephalography techniques to study and record the brain activity of a group of adult volunteers in the face of manipulations of a magnetic field carried out by scientists in a closed and isolated environment, a Faraday cage.

Feeling the magnetic field
It should be noted that until now, most of the scientific evidence of magnetoreception has been based on changes in the behaviour or movement patterns of animals in the face of magnetic variations in their environment. In other words, scientists now know that animals are able to “feel” the magnetic field, but they still have no idea how they do it at the cellular or neuronal level.

The barrier that separates what we know from what is unknown seems to be in biology, that is, in how exactly the brain is able to use the “magnetic” information it receives. As early as 2012, David Dickman, a neurobiologist at the University of Houston School of Medicine, demonstrated that a series of specific neurons in pigeons’ inner ears are involved in some way in the response of those animals to changes in the direction, polarity or strength of magnetic fields.

But pinpointing exactly where the magnetoreceptors responsible for triggering those responses are has been like looking for a needle in a haystack. In fact, no specific “sensory organ” has been found that scientists could dissect and study. Since magnetic fields are ubiquitous, they constantly sweep all over the body, all the time. The receptors, then, could literally be anywhere.

In this sense, it is thought, for example, that in pigeons (as well as in some fish and bacteria), the magnetic sensor consists of a series of iron oxide crystals (magnetite) connected in some way to other organelles that Science still does not fully understand. In bees, on the other hand, magnetite is located in the membranes of certain types of neurons, and even human beings.

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