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Humans can have a sixth sense to detect the Earth's magnetic field. Known as magneto-pendence, this meaning is one of the ways that birds and fish can travel enormous distances with surprising accuracy – an integrated compbad for travel around the world. But until now, this had not been observed in humans.
Researchers from the California Institute of Technology and the University of Tokyo researched this ancient meaning by recording the brainwaves of 29 participants through electroencephalography (EEG). They measured alpha waves, which are the dominant brain waves observed when humans rest and treat no sensory inputs. When our senses are stimulated, whether our vision, our hearing or our sense of touch, our alpha rhythms collapse.
The participants sat in a Faraday cage, which blocks all electronic and magnetic interference, and the researchers used a series of electric coils to create artificial magnetic fields. The vertical component of the Earth's magnetic field was maintained as usual and the researchers manipulated the horizontal component, which simulated what would happen when a participant turned their heads left or right. When the magnetic field has been changed, participants experience a fall in alpha beats. The researchers learned that participants' brains perceived this change in magnetic field, with alpha rhythms reacting as they would in front of a visual, sonic or tactile stimulus.
Joe Kirschvink, a Caltech geophysicist and one of the authors of the study, suggests a way in which this could happen in our brain. Magnetite, iron crystals found in human cells, could be affected by the Earth's magnetic field, such as miniature compbad needles. This is a phenomenon that has been observed in many sentient creatures in the north.
"Many animal tissues make tiny magnetic crystals," said Kirschvink. "The best example is the magnetotactic bacterium. There is enough magnetite in their cells to force them to align with the Earth's magnetic field. So, what we're saying is that there are cells containing tiny magnetite crystals that do it somewhere in the nervous system and send signals to our brain. "
Participants could not consciously perceive changes in the strength of the magnetic field even though they were undergoing changes in their alpha waves. This could mean that our magnetosensory systems might lack a component allowing us to consciously perceive this meaning.
"The brain perceives a lot of things we are not aware of," Kirschvink said. "In fact, the trigeminal nerve, which we think it brings this information, most of its sensory inputs are not in our consciousness. On the other hand, there may be humans who are aware of it and we have not found them yet. "
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