Humans may have a sixth sense enabling them to sense Earth’s magnetic field. Known as magnetorecepetion, the sense is one of the ways birds and fish are able to navigate huge distances with surprising accuracy – a built-in compass for journeys across the globe. But until now, it hadn’t been seen in humans.
Researchers from the California Institute of Technology and the University of Tokyo searched for this ancient sense by recording the brain waves of 29 participants using electroencephalography (EEG). They were measuring alpha-waves, which are the dominant brain waves seen when humans are resting and not processing any sensory input. When our senses are stimulated, whether it’s our vision, hearing, or sense of touch, our alpha-rhythms drop.
The participants sat inside 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 normal, and the researchers manipulated the horizontal component, which simulated what would happen when a participant turned their head to the left or right. When the magnetic field was changed, participants experiences a drop in alpha-rhythms. This told the researchers that the participants’ brains were perceiving this change in magnetic field, with alpha-rhythms reacting just as they would to a sight, sound or touch stimulus.
Joe Kirschvink, a geophysicist at Caltech and one of the authors of the study, proposes a way that this could be happening inside our brains. Magnetite, iron crystals found in human cells, could be affected by the Earth’s magnetic field like miniature compass needles. It’s a phenomenon that’s been seen in many north-sensing creatures.
“Many animal tissues make tiny magnetic crystals,” Kirschvink said. “The best example is the magnetotactic bacteria. There’s enough magnetite in their cells to passively torque them into alignment with Earth’s magnetic field. So what we’re saying is that there are cells containing tiny magnetite crystals that are doing this somewhere in the nervous system and sending signals to our brain.”
The participants couldn’t consciously perceive the changes in magnetic field strength even though they were experiencing changes in their alpha-waves. This might mean that our magnetosensory systems might be lacking a component that allows us to consciously perceive this sense.
“The brain perceives a lot of things that we’re not consciously aware of,” Kirschvink said. “In fact, the trigeminal nerve, which we think is bringing in this information, most of its sensory inputs are not within our conscious awareness. On the other hand, there may be humans who are aware of this and we just haven’t found them yet.”