Each spring, flocks of migratory birds travel northward from their sunny vacations in the south, following a flight plan that’s ingrained in their DNA. Birds — like bats, bees, wolves, bears, and countless other animals — have the ability to use the Earth’s magnetic field as a map to navigate the planet. We humans seem directionless in comparison, but as new research in eNeuro suggests, it’s probably not because we lack the tools.
A team including Caltech geoscientist Joseph Kirschvink, Ph.D., and neuroscientist Shin Shimojo, Ph.D., show in the new paper that the human brain responds to changes in the electromagnetic field, even if humans don’t realize it.
“Our results indicate that human brains are indeed collecting and selectively processing directional input from magnetic field receptors,” they write in their preprint on biorXiv.
The Earth’s electromagnetic field is generated by electric currents created from the swirling molten iron in its core. In the northern hemisphere, all field lines are oriented toward magnetic north, and ditto for the south. Those lines are what birds and their field-reading kin use to navigate — and, as the new evidence suggests, humans may be able to sense them too. When participants in the study went through simulated shifts in the Earth’s magnetic field, their brain activity reacted in predictable patterns, suggesting the human body is equipped for magnetoreception, even if we’re not aware of it.
It’s impossible to shift the planet’s actual magnetic field, so the team built a highly insulated chamber in which they could create “ecologically relevant rotations of Earth-strength magnetic fields” for the person sitting inside it. As the team rotated the magnetic field, they also measured the electrical activity of the participants’ brains using electroencephalography (EEG).
In some people, with each rotation of the field, the team noticed a pattern neuroscientists have documented before: a sudden drop in amplitude in the alpha oscillation, the main brain wave on an EEG of a person at rest. That drop, called an “alpha event-related dysynchronization” (or alpha-ERD for short), is usually observed when a person is suddenly confronted with an external stimulus, whether visual, auditory, or physical. The participants didn’t know their brains were reacting, but their EEGs gave it away.
In total, 34 people “from the Caltech population” participated in the various experiments, in which the magnetic field was shifted in a range of directions, rotated, or not manipulated at all. Four of those people, the team writes, had especially stable alpha-ERDs even over follow-up experiments, suggesting their brains were always attuned to changes in the “normal” magnetic field. The other responses were more variable, though the general pattern of alpha-ERDs occurring in response to magnetic field shifts was clear.
Interestingly, the tests confirmed these people were attuned to magnetic north, as they were conducted in the northern hemisphere. A successful southern hemisphere follow-up experiment would further support their hypothesis.
The changes in brain activity, as Kirschvink told The Guardian, represent the brain “freaking out” in response to sudden changes in the environment. However, it’s still not clear how the brain is picking up on the magnetic field. Some researchers have suggested that retinal proteins called “cryptochromes” might react to the magnetic field, but Kirschvink predicts the body might contain specialized magnetosensory cells housing iron clusters that move like the needle of a compass. Unfortunately, finding these magnetosensory receptors has been compared to finding a needle in a haystack. “The receptors could be in your left toe,” Kirschvink told Science in 2016.
There’s a lot left to learn about where this ability to sense the magnetic fields came from, how it might have been used, and why we can’t use it anymore. But this study is an important first step in exploring an innate part of ourselves that we didn’t know existed. The timing couldn’t be better, as some scientists warn that we are overdue for a major shift in the Earth’s magnetic field.
“For now,” the team writes, “alpha-ERD remains a blank signature for a wider, unexplored range of magnetoreceptive processing.”
Magnetoreception, the perception of the geomagnetic field, is a sensory modality well established across all major groups of vertebrates and some invertebrates, but its presence in humans has been tested rarely, yielding inconclusive results. We report here a strong, specific human brain response to ecologically-relevant rotations of Earth-strength magnetic fields. Following geomagnetic stimulation, a drop in amplitude of EEG alpha oscillations (8-13 Hz) occurred in a repeatable manner. Termed alpha event-related desynchronization (alpha-ERD), such a response is associated with sensory and cognitive processing of external stimuli. Biophysical tests showed that the neural response was sensitive to the dynamic components and axial alignment of the field but also to the static components and polarity of the field. Thispattern of results implicates ferromagnetism as the biophysical basis for the sensory transduction and provides a basis to start the behavioral exploration of human magnetoreception.