June 22, 2011

Human Retina Can Sense Earth’s Magnetism

Research published this week in the journal Nature Communications shows that a light-sensitive protein found in the human eye can act as a "compass" in the magnetic field when implanted into the eyes of Drosophila (flies).

The study showed that without their natural "magneto reception" protein, flies do not respond to a magnetic field. But after replacing the protein with a human version of the protein, their ability was restored.

For migratory birds and some other animals, the ability to sense the Earth's magnetic field is crucial for navigation of long distances during migration. Humans, however, are assumed to not have this unique ability. But the research by scientists at the University of Massachusetts Medical School shows that the protein expressed in the human retina can sense magnetic fields in other species, namely flies. The concept reopens an area of sensory biology that has been worked on in the past by other research teams, notably by Robin Baker of the University of Manchester in the 1980s.

Baker used a long series of experiments on thousands of volunteers that suggested humans could indirectly sense magnetic fields, though he never was able to identify the mechanism. In years since, many teams tried to replicate Baker's studies, with opposing results.

In many migratory animals, the light-sensitive chemical reactions involving flavoprotein cryptochrome (CRY) are thought to play an important role in the ability to sense Earth's magnetic field. In past studies of Drosophila, scientists at the university's Reppert lab have shown that the CRY protein found in the flies can function as a light-dependant magnetic sensor.

To test whether the human CRY 2 protein (hCRY2) has similar magnetic sensory ability to migratory animals, Steven Reppert MD, the Higgins Family Professor of Neuroscience and chair and professor of neurobiology, graduate student Lauren Foley, and Robert Gegear PhD, a post doctoral fellow in the Reppert lab now an assistant professor of biology and biotechnology at Worcester Polytechnic Institute, created a transgenic Drosophila model without a CRY protein but replaced with a hCRY2 protein instead.

Reppert's team utilized a previously developed behavioral system to show that the transgenic flies were able to sense and respond to an electric-coil-generated magnetic field and do so in a light-dependant manner.

The team's findings demonstrate that hCRY2 has the molecular capability of sensing magnetic fields and could lead to further probes into human magnetoreception.

"Additional research on magneto sensitivity in humans at the behavioral level, with particular emphasis on the influence of magnetic field on visual function, rather than non-visual navigation, would be informative," wrote Reppert and his colleagues in the study.

"We developed a system to study the real mechanism of magnetosensing in fruit flies... we can put these proteins from other animals into the fly and ask, 'do these proteins in their different forms actually function as magnetoreceptors?'" Reppert told BBC News.

"Of all the vertebrates, the one that seemed to make the most sense was trying to put in the cryptochrome from humans," said Reppert.

Reppert added that he would be "very surprised" if humans did not have the sense of magnetoreception. "It's used in a variety of other animals. I think that the issue is to figure out how we use it," he said.

Baker maintains his results prove that human magnetoreception was "overwhelming," but hopes that the new findings bring more interest into finding a final solution to the matter. "I think one of the things that put people off accepting the reality of human magnetoreception 20 years ago was the lack of an obvious receptor," he told BBC News.

"So these new results might actually be enough to tip the balance of credibility. I shall be fascinated to see," he told BBC News.


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