Many animals can detect magnetic fields, but can we?
We have evolved to detect a range of sensory inputs, including light, sound, and odors.
Other members of the animal kingdom have developed sensitivities that seem to lie beyond our capabilities.
Many species, including certain bacteria, birds, molluscs, and marine mammals, demonstrate magnetoreception — meaning that they can detect fluctuations in magnetic fields.
They use this ability to orient themselves in the environment and to navigate.
In the 1980s, there was a flurry of research investigating whether humans could detect these subtle shifts, but the results were contradictory and proved difficult to replicate.
The debate quietened down. Recently, however, scientists at the California Institute of Technology in Pasadena and the University of Tokyo in Japan decided that the time was right to revisit magnetoreception in humans.
A new approach
In the 40 years that followed the initial burst of interest in human magnetoreception, scientists have developed a far more detailed picture of how the sense works in animals.
Scientists have learned that some animals use a twopronged approach to navigate using magnetic fields: a compass and a map response. The compass response simply uses the field to orient the animal relative to the local north/south direction.
The magnetic map is more detailed; it uses field intensity and direction to build a picture of where the animal is relative to where it wants to go.
It seems clear that if we can detect magnetic fields, we are not conscious of it. The authors of the recent study believe that this is the primary reason that earlier studies have failed — they were looking for behavioral responses to something that humans probably detect subconsciously.
Over recent decades, brain scan technology has come on leaps and bounds. It is now possible to measure brain activity far more precisely than ever before.
So, rather than looking for behavioral responses, the scientists decided to measure responses in the brain directly. They published their intriguing findings in the journal eNeuro earlier this week.
Watching alpha rhythms
The researchers used EEG scanning technology to investigate brain activity. At the same time, they manipulated the magnetic field within an isolated, radiofrequency-shielded chamber. They paid particular attention to the participants' alpha rhythm. Explaining why, they say:
"The alpha rhythm is the dominant human brain oscillation in the resting state when a person is not processing any specific stimulus or performing any specific task [...]. When an external stimulus is suddenly introduced and processed by the brain, the alpha rhythm generally decreases in amplitude."
Scientists call this measurable change in activity "alpha event-related desynchronization." As they expected, they found that in some participants, there was a decrease in alpha event-related desynchronization when the magnetic field changed.
However, the magnitude of the response varied greatly between participants.
In the second set of experiments, the researchers focused on the participants with the most robust responses to changes in magnetic field.
By examining these people, they could confirm that their responses were tuned to the magnetic field of the Northern Hemisphere, where the study took place. The authors conclude:
"Our results indicate that human brains are indeed collecting and selectively processing directional input from magnetic field receptors."
This has been a hot topic in the scientific community for decades. Therefore, it will take more than one study to prove definitively that humans can detect changes in the earth's magnetic field.
However, if scientists do finally prove that humans can detect magnetic fields, would it be such a shock? As the authors write:
"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."
"The full extent of this inheritance remains to be discovered."