What do birds and bees, worms and wolves, fruit flies and fish all have in common? The answer: a magnetic sense that helps them navigate. Now it seems we might do as well.
Joseph Kirschvink at the California Institute of Technology in the US and colleagues found that altering the directions of nearby magnetic fields caused temporary changes in human brain activity.
While sitting still in a dark room, participants’ brain activity was recorded using electroencephalography (EEG), while electromagnetic coils were used to create magnetic fields.
The experiment mimicked the magnetic field changes we are subject to when we move about in the real world, says Kirschvink.
The direction and intensity of Earth’s magnetic field varies by geographical location. For example, at the magnetic north pole, one of two poles where the magnetic field is the strongest, the direction of the field points vertically downwards, into the ground.
In the wider northern hemisphere, this vertical angle changes but the magnetic field is always skewed downwards – meaning that when you hold a compass horizontally, the end pointing north is slightly pulled down. The south-pointing end of some compasses in the northern hemisphere are weighted to compensate for the pull.
When the team exposed people to a downward-pointing magnetic field, they saw changes in brain wave patterns when they rotated the field horizontally in a counterclockwise direction .
The team measured alpha waves – present when we are awake but relaxed and with closed eyes – before and after a 100 millisecond change in magnetic field, and found a drop in amplitude in the waves in some people following the rotation.
But no participants showed brain changes when the magnetic field was rotated clockwise, a finding the researchers can’t explain.
Rotating an upwards-pointing magnetic field didn’t cause a change either, which the team speculates may be because the participants’ brains were attuned to the magnetic field of the northern hemisphere, where they conducted the study. Earth’s magnetic field always points up in the southern hemisphere.
“One interesting way to test this hypothesis would be to reproduce our experiment in the southern hemisphere,” says team member Isaac Hilburn.
Claims that humans can detect magnetic fields has long been a source of controversy, but other researchers are cautiously optimistic about the new work.
The team’s approach parallels studies of magnetoreception in animals, says Nathan Putman at LGL, an ecological research firm based in Bryan, Texas. Putman, who studies marine animals including turtles, says the strongest evidence for a magnetic sense is when animals change their direction of travel in response to an altered field.
The possibility that humans could have a magnetic sense is exciting, but the results will need to be replicated, he says. “A sceptic could argue that there’s a lot of reasons why brain waves might change and it may not have anything to do with orientation.”
It is possible the EEGs could have picked up disruptions from the surrounding environment, says Can Xie at Peking University in China, although the study tried to eliminate this, he says. “It is hard to interpret the EEG signal precisely, which makes it difficult to further explore the underlying molecular mechanism at this stage.”
If the results hold up, it may mean that a magnetic sense played a role in the nomadic lives of our hunter-gatherer ancestors, says Hilburn.