The Student
Humans may be able to sense the magnetic field of the earth

Humans may just have become members of a very eclectic club. Fruit flies, homing pigeons, bats, mole-rat, and turtles are among the diverse creatures unified by an intriguing characteristic: the ability to detect the earth’s magnetic field. Now, for the first time, there is compelling evidence to suggest that humans might also unknowingly share this ability.

The data comes from a group based at the California Institute of technology, led by Joseph Kirschvink. In the study, participants were sat in a dark room and monitored using electroencephalography (EEG), a technique that measures the electrical activity of the brain through electrodes placed on the scalp. EEG measures alpha waves, which are the relatively low- frequency pulses of electricity generated by neurons when the brain is in a more restful state. If brainwaves were music notes, alpha waves would be a low, slow hum in comparison to the shrill rapid- fire beta waves that dominate when we’re more active.

Participants were sat in a testing chamber which allowed the researchers to alter the magnetic field they were experiencing with no other changes that might alert the subjects to the difference. According to Kirschvink, these changes in the magnetic field are similar to what we might experience as we move around in the world. The group observed that this alteration of the magnetic field triggered a sudden reduction in the participant’s alpha waves, a reaction which normally occurs when the brain has become alert in response to a sensory stimulus.

These results provide the first compelling evidence that the human brain can detect changes in magnetism without other cues. Interestingly, though, the brain waves only seemed to change when the magnetic field was moved in certain directions. When the team exposed participants to a downwards pointing magnetic field, as one would experience standing in the northern hemisphere, they saw a brain response after moving the field horizontally in a counterclockwise direction, but not a clockwise direction. Moreover, the brain waves did not respond to changes when the magnetic field was pointing upwards.

The group believes this variation in the response could reflect the brain’s attempt to “filter” for relevant magnetic changes. As the participants were from the northern hemisphere, it could be that their brains were naturally attuned to the downward facing field, and so this is what they responded to. “It makes sense to reject any magnetic signal that is too far away from the natural values because it most likely is from a magnetic anomaly – a lighting strike, or a lodestone deposit in the ground, for example.” Kirschvink explains. The team are now considering repeating the experiment in the southern hemisphere to test this hypothesis.

Though exciting, the study is not without its critics. “A sceptic could argue that there are a lot of reasons why brain waves might change and it may not have anything to do with orientation” says Nathan Putman, who works at ecological research firm LGL.

Can Xie, from Peking university in China, has raised concerns about the danger of EEG scanners picking up external stimuli from the environment. “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 data stands the test of time, it will open up questions about the role of a possible “magnetometer” in humans. Many animals use their sense of the magnetic field as a kind of internal GPS, allowing them to navigate as they move throughout the world. Studies have shown that some organisms, honeybees for example, respond to changes in magnetism with the same strength that they respond to changes in stimuli such as touch or smell. There is even some evidence that migratory birds can actually “see” a visual representation of the earth’s magnetic field, using a special type of light receptor protein which can identify changes in light patterns caused by magnetism.

It is possible that we could have relied upon a magnetic sense more as hunter-gatherers, long before the cultural revelations of google maps and satellite navigation systems. Certainly though, the the question of how magnetoreception could continue to play a role in our perception of and response to the environment is a fascinating one, an intriguing development in our understanding of the capabilities of the human brain.

Image credit: Windell Oskay via Flickr