Mental compass: New evidence suggests humans can sense Earth's magnetic field
Magnetoreception, or the ability to sense the Earth's magnetic field, pops up throughout the animal kingdom, but it's generally thought to be something humans missed out on. But maybe we can after all. New research out of Caltech has found changes in human brain wave activity that seems to be in response to a changing magnetic field.
Bees, birds, bats, whales, turtles, salmon and eels are known to navigate by sensing the geomagnetic field. Humans, on the other hand, aren't really thought to have that ability – at least not without some kind of wearable or implantable gadget. But some scientists believe we do have that innate sense to some degree, but so far nobody's been able to prove it conclusively.
"Aristotle described the five basic senses as including vision, hearing, taste, smell, and touch," says Joseph Kirschvink, co-corresponding author of the new study. "However, he did not consider gravity, temperature, pain, balance, and several other internal stimuli that we now know are part of the human nervous system. Our animal ancestry argues that geomagnetic field sensors should also be there representing not the sixth sense but perhaps the 10th or 11th human sense to be discovered."
To investigate, the Caltech team ran experiments on 34 participants of different ages and ethnicities. Since any sensing of the magnetic field would of course be subconscious, the team attached 64 electrodes to each participant's head to record their brain waves. Specifically they were looking for the "alpha rhythm," which is high when a person isn't focused on anything in particular but drops when a stimulus catches their attention.
The idea is that if the alpha rhythm dips when a magnetic field is switched on around a participant, that would be evidence of human magnetoreception. To remove other stimuli that might cause the dips, the researchers had participants sit in a dark, silent room for an hour at a time.
The researchers turned on magnetic fields and rotated them around the room, and watched the brain waves of the test subjects. And sure enough, as soon as the magnetic field was switched on, the alpha power dropped in some participants, by as much as 60 percent. The dip occurred over a few hundred milliseconds, before returning to normal. This, according to the researchers, is an expected and well-documented brain wave response to stimuli, known as alpha event-related desynchronization (alpha-ERD).
"Alpha-ERD is a strong neural signature of sensory detection and the resulting attention shift," says Shin Shimojo, co-lead author of the study. "The fact that we see it in response to simple magnetic rotations like we experience when turning or shaking our head is powerful evidence for human magnetoreception. The large individual differences we found are also intriguing with regard to human evolution and the influences of modern life. As for the next step, we ought to try bringing this into conscious awareness."
The team took plenty of steps to ensure that participants weren't sensing other things. The test chambers were shielded from outside electromagnetic signals, and the copper wires that generated the magnetic field were wrapped so they wouldn't produce an audible hum.
Interestingly, the researchers found that it only registered when the vertical component of the field was pointing downwards, and not when it was pointing up. This, they say, could be the brain actively processing the information and ignoring what it thinks is "unnatural." In the Northern Hemisphere, where the experiment was conducted, the Earth's geomagnetic field points down, so locals are used to that. One way to validate the find would be to repeat the experiment in the Southern Hemisphere, where local brains should exhibit the opposite pattern.
Of course, 34 participants isn't a huge sample size, and even then it only worked on some people. The researchers say the experiment would need to be replicated and expanded to test more people for magnetoreception.
The research was published in the journal eNeuro.