It’s a process that allows pigeons, honey bees and whales to navigate the world through the Earth’s magnetic field. Magnetoreception, a so-called sixth, geomagnetic sense, is found in bacteria, arthropods and multiple vertebrate species. It was thought to be completely beyond the perception of beings humans.
A new study by researchers at the California Institute of Technology (Caltech) addresses the question posed by lead author Connie Wang.
“Many animals have magnetoreception, so why not us?” Wang said in a press release.
The findings provide evidence that the human brain is capable of geomagnetic sensing.Many early studies in magnetoreception center around the presence of magnetite, a kind or iron ore, somewhere within the organism or cell. Magnetite, as the name implies, is sensitive to the magnetic field of the earth and can allow organisms to tell where they are and where they need to go.
Magnetite is also found in the human brain, but it is unclear whether it performs the same function in all organisms or whether it has something to do with the apparent geomagnetic sensing shown experimentally in the Caltech study.
In collaboration with the University of Tokyo, Caltech researchers provided experimental evidence that brain waves in humans respond to changes in “Earth-strength” magnetic fields.
After testing 34 participants, they found that some individuals had a decrease in alpha wave power that correlated with exposure to a magnetic field, which suggests that some humans might be unconsciously preceptive of geomagnetism.
Wang, a graduate student at Caltech, conducted the study with Joseph Kirschvink, a Caltech geoscientist; Shin Shimojo, a Caltech neuroscientist; and Ayu Matani, a University of Tokyo neuroengineer. The research team published their findings in eNeuro on March 18.
Their method included building an isolated radiofrequency-shielded chamber in which each of the participants (who varied in age and ethnicity) sat under it in silence and darkness for one hour with electrodes attached to their heads. During the hour, researchers would silently shift a magnetic field around the chamber while monitoring the participant’s brain waves.
While the participants did not consciously experience any changes, many had a change in the alpha rhythms of their brains seconds after exposure.
Alpha waves are a measure of whether the brain is engaged or unengaged. When the brain perceives something, even if it is unconscious, the amplitude or power of the wave drops.
In the Caltech study, this drop in amplitude correlated with the movement of the magnetic field in some individuals. Immediately after exposure to the magnetic field, the alpha power could drop by as much as 60 percent before returning to the baseline a few seconds later. A similar drop in amplitude also happens when humans use other senses like touch and hearing.
Further tests showed that the brain also had different responses to natural and unnatural magnetic signals. There were only changes in alpha power when the vertical component of the magnetic field was pointed downward, which is the normal order of things in the Northern Hemisphere. When the researchers tilted the field upward, there was no change in amplitude.
Kirschvink suggests that the same experiment should be performed in the Southern Hemisphere to see if the brain is actively processing the signals it is exposed to, or whether such tests would reveal a different result because of the different magnetic field.
Among the biggest challenges when studying human magnetoreception is making sure that the observed effects are actually due to the researchers’ controlled stimuli. Because alpha power drops in response to the normal five senses, something as small as a hum or change in light could be responsible for an observed effect.
The Caltech team controlled for this by using a completely dark, isolated chamber with wires and other components cemented into place and duplicated. Not only do the results challenge notions of what the human brain is capable of detecting, but they also set a precedent for future magnetoreception studies.
In the press release, Kirschvink expanded upon the implications of the team’s results.
“Given the known presence of highly evolved geomagnetic navigation systems in species across the animal kingdom, it is perhaps not surprising that we might retain at least some functioning neural components, especially given the nomadic hunter-gatherer lifestyle of our not-too-distant ancestors,” he said. “The full extent of this inheritance remains to be discovered.”
