Magnetoreception: Can the Human Brain
Detect the Earth’s Magnetic Field?
There has been much controversy over whether or not human beings are magnetically sensitive organisms. Scientists have already shown that animals have a geomagnetic sense, so why shouldn’t humans? A team of geoscientists and neurobiologists set out to prove just that.
Creatures with a geomagnetic sense
The invisible force field that surrounds the Earth and is generated deep inside the planet’s core is called the geomagnetic field. At the Earth’s surface, this magnetic field is fairly weak, yet in the last 50 years, scientists have shown that hundreds of animals, including birds, sea turtles, insects, fish, reptiles, butterflies and many other migratory and homing animals, have very strong behavioral responses to the geomagnetic field. In fact, the ability animals have to detect and respond to the geomagnetic field makes up a part of their biological navigation system, along with their senses of sight, smell and hearing. This interaction with the Earth’s magnetic field, thus, greatly influences animal behavior and is vital for their survival.
The experiments done on animals provided a basis for testing on human beings. “Magnetoreception, the perception of the geomagnetic field, is a sensory modality well-established across all major groups of vertebrates and some invertebrates. Many past attempts have been made to test for the presence of human magnetoreception using behavioral assays, but the results were inconclusive,” say geoscientist Joseph Kirschvink and neuroscientist Shin Shimojo. Consequently, Kirschvink, Shimojo and their team at Caltech and the University of Tokyo recently conducted a study using electroencephalography techniques (EEG) to see whether or not the human brain would passively react to magnetic field changes. Their results were published in the journal eNeuro.
Evidence for human magneto-
reception: The experiment
The study consisted in recording the brain activity of 34 adult participants during magnetic field manipulations. The research team built an isolated, radiofrequency-shielded chamber where sets of coils were housed inside a modified Faraday cage. One at a time, participants were asked to sit upright in a wooden, nonmagnetic chair with their heads facing North and with their eyes closed. Researchers then shifted the magnetic field inside the chamber while the battery-powered EEG machine relayed brain activity to a remote control room 20 meters away.
Participants had no perception of these shifts throughout the entire experiment. They simply sat, passively, in the dark while their brains registered the shifts subconsciously. Each participant, however, registered different amounts of activity. Some brains showed almost no reaction at all while other brains perceived the unexpected change in the natural direction of the magnetic field and registered a considerable reduction in alpha brain waves after the shift.
EEG data, thus, revealed that the human brain collects and selectively processes directional input from magnetic field receptors. A reduction in alpha brain waves as a response to minimal shifts in the direction of the magnetic field is an indication of human magnetoreception. “In our experiment, alpha-ERD shows that the human brain can detect Earth-strength magnetic fields, demonstrating that we have a sensory system that processes the geomagnetic field all around us,” Kirschvink and Shimojo said. It was, thus, concluded that the human brain can unconsciously respond to changes in the Earth’s magnetic fields.
Implications of the experiment for the future
For now, the experiment has demonstrated that human beings have working magnetic sensors that send signals to the brain. Further research must be done to see what this implies for human behavioral capabilities. It is also unclear why some brains register stronger responses to shifts in the magnetic field than others and whether or not brains with weaker responses can be trained to react with stronger responses. Research must also be done to determine whether or not these differences in brain activity depend on positional cues or even individual genetic or developmental diversity. Future experiments will need a wider survey of individuals, even from distinct populations, for further investigation.
In many animals, a geomagnetic sense has been found and shown necessary for navigational behavior. It is possible that our past ancestors, given their nomadic hunter/gatherer lifestyle, may have also depended on a geomagnetic navigation system, but our modern environment may have interfered and encouraged its disuse. Humans may no longer need to rely on an internal navigational sense for survival as there are now many external cues such as landmarks, streets and technology that act as our guides. Even still, magnetoreceptive responses may have a great impact in situations where other cues are weak, such as in sea or air navigation, where spatial disorientation occurs quite frequently. The full implications of this innate sensory system remain to be discovered.
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