A new study from researchers at the California Institute of Technology suggests that humans can sense the Earth’s magnetic field. “We have not as a species lost the magnetic sensory system that our ancestors [millions of years ago] had,” said Prof Joseph Kirschvink, leader of the research from the California Institute of Technology. “We are part of Earth’s magnetic biosphere.” The Guardian reports: Writing in the journal eNeuro, Kirschvink and colleagues in the U.S. and Japan describe how they made their discovery after building a six-sided cage, the walls of which were made of aluminium to shield the setup from electromagnetic interference. These walls also contained coils through which currents were passed to produce magnetic fields of about the same strength as Earth’s. Each participant was asked to enter the cage and sit still on a wooden chair in the dark, facing straight ahead towards the north. During the experiment, the team measured the participant’s brain waves using an electroencephalogram (EEG).

In some experiments the applied magnetic fields were fixed in one direction, while in others they were rotated. In still others the machines were turned on but no magnetic field was produced — meaning the participant was only exposed to Earth’s natural magnetic field. The participant was unaware which experiment was under way. The results, gathered from 34 adult participants, revealed that certain scenarios triggered a drop in participants’ alpha brain waves — a change that is linked to the brain processing information. This occurred if the applied magnetic field was pointed north and then swept upwards or downwards, or directed down while pointing north and rotated anticlockwise. That is similar to a human in the northern hemisphere nodding their head, or turning their head to the right respectively. Kirschvink said the responses showed that the brain was clocking an unexpected change in the environment. “Crucially, he said, it means that humans must be ale to detect such changes — although the strength of the response varied hugely among participants,” reports The Guardian. The authors say the new research suggests the human system can tell north from south via a mechanism involving special cells containing iron-based crystals. “These crystals are thought to rotate rather like the needle of a compass, opening or closing pores in the cells, thereby affecting signals being sent to the brain,” the report adds.

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