Some animals, such as sea turtles or birds, have magnetoreception skills, that is, they are able to sense the Earth’s magnetic field and use it for navigation. Now, a new study suggests that humans also have this magnetic sense. The work, which has been published in the journal eNeuro , suggests that when people’s brain waves are surrounded by different magnetic fields, we have a “sixth sense” for magnetism.
Scientists have long wondered whether humans could also possess this type of magnetoreception that fish and birds have. By exposing a group of people to a magnetic field with Earth’s forces pointed in different directions in the laboratory, researchers from the United States and Japan discovered different patterns of brain waves that are produced in response to the rotation of the magnetic field.
These findings offer evidence that people unconsciously respond to the Earth’s magnetic field, although it is not yet clear exactly why or how our brains use this information.
A step forward for the human magnetic sense
During the experiment, 26 participants sat blindfolded in a quiet, dark chamber filled with electrical coils. These coils manipulated the magnetic field inside the chamber so that it remained with the same force as Earth’s natural field, but could point in any direction. The participants wore an EEG (electroencephalography) cap that recorded the electrical activity of their brains as the surrounding magnetic field rotated in various directions.
This setup simulated the effect of someone spinning in different directions on Earth’s natural, unchanging field without requiring a participant to actually move. (Complete stillness prevented motor control thoughts from affecting brain waves due to the magnetic field.) The researchers compared these EEG readings with those from control trials where the magnetic field within the chamber did not move.
Did the brain react to changes in the direction of the magnetic field? Alpha waves generally dominate EEG readings when a person is inactive, but fades when someone receives sensory input, such as a sound or a touch.
Of course, changes in the magnetic field caused changes in people’s alpha waves. Specifically, when the magnetic field was pointed toward the ground in front of a participant facing north (the direction that Earth’s magnetic field is pointing in the northern hemisphere), the field’s spin in a counter-clockwise direction from northeast to the northwest caused an average drop of 25% in the amplitude of the alpha waves. That change was approximately three times stronger than the natural alpha wave fluctuations observed in the control trials.
Interestingly, the brains of the participants showed no responses to a rotating magnetic field oriented toward the ceiling, the direction of Earth’s field in the southern hemisphere. Four participants were retested weeks or months later and showed the same responses.
If these findings are replicable, they raise several questions, such as why people seem to respond to fields that point downward but not upward.
“The brain is capturing magnetic data, extracting it and using it only if it makes sense,” suggest the authors of the work.
The participants in this study, who hailed from the Northern Hemisphere, should perceive downward-pointing magnetic fields as natural, while upward fields would constitute an anomaly, the researchers argue. Magneto-receptive animals are known to turn off their internal compasses when they encounter strange fields, such as those caused by lightning, that could deflect the animals. Northern-born humans can also take their magnetic sense “out of line” when faced with strange fields pointing upward. This explanation seems plausible, but it would have to be tested in an experiment with participants from the southern hemisphere, they point out.
Even taking into account what magnetic changes the brain recovers, researchers still don’t know what our minds can use that information for. Another persistent mystery is how, exactly, our brains detect the Earth’s magnetic field. According to the researchers, the brain wave patterns discovered in this study can be explained by sensory cells that contain a magnetic mineral called magnetite, which has been found in magnetoreceptive trout and the human brain. Future experiments could confirm or eliminate that possibility.
We have just taken the first step in understanding what the human magnetic sense appears to be.
Referencia: C.X. Wang et al. Transduction of the geomagnetic field as evidenced from alpha-band activity in the human brain. eNeuro. Published online March 18, 2019. doi:10.1523/ENEURO.0483-18.2019.
