Caltech researchers have discovered tiny magnetic particles in the brains of humans, similar to those that have been found in other animals.
"This is the first new material that has been found in humans since our ancestors found blood, guts and bones," biologist Joseph L. Kirschvink said at a news conference Monday.
In many other species, such as pigeons, salmon and whales, the magnetic particles allow the organisms to navigate in Earth's magnetic field, providing an inborn sense of direction. But it is not yet clear whether humans have the same ability, Kirschvink said.
"We don't know what the magnets do or where they hide in cells," he added, but their discovery could help explain the reported link between cancer and the electromagnetic fields produced by power lines and appliances.
"It's a very interesting result, but we don't know what it means yet," said physicist Richard Frankel of Cal Poly San Luis Obispo, who discovered similar particles in bacteria in 1975.
If the size and configuration of the magnetic particles are identical to those of the particles in other species, as they appear to be, "that's very suggestive that it is playing an orientational role," said biologist James Gould of Princeton University. That ability could have been more important at an early stage of human evolution and withered away from lack of use, experts said.
The magnetic particles are composed of magnetite, a naturally occurring mineral also known as lodestone. The particles found by Kirschvink and his colleagues, research engineer Atsuko Kobayashi-Kirschvink and USC anatomist Barbara J. Woodford, are extremely tiny. They range from a millionth of an inch to a hundred-thousandth of an inch in diameter.
Tissue from seven human brains was dissected by Woodford using ceramic or Teflon-coated scalpels to avoid possible metallic contamination, which has marred previous searches for the particles. The tissue was then studied in a specially constructed clean room at Caltech that is shielded from external magnetic fields by six tons of steel in the walls, floor and ceiling.
Using very sensitive magnetometers, Kirschvink and his colleagues were able to show that the brain tissue had the "unmistakable signature" of magnetite. They then dissolved the tissue and were able to isolate the magnetite particles by allowing them to become attached to a glass wall surrounding a powerful magnet. That isolation "was the most convincing thing he did," Frankel said.
The particles are virtually identical to those found in other organisms. They seem to be distributed throughout the brain, but the highest concentration is in the meninges, the membrane that encloses the brain. The total amount present in the brain is about one-millionth of an ounce, much less than the amount of non-magnetic iron in the brain in the form of oxygen-carrying hemoglobin and ferritin, an iron storage compound.
Other organisms use the magnetic particles to navigate. Bacteria, for example, use the fields to find their way down to mud at the bottom of ponds, where they obtain their nutrients. Homing pigeons use the fields to find their way home, as do whales and salmon. Experiments have shown that the ability of a pigeon to navigate can be blocked by attaching a powerful magnet to its head, preventing it from sensing Earth's magnetic field.
In 1980, zoologist R. Robin Baker of the University of Manchester in England reported that humans also have an innate directional sense that can be confused with magnets. But despite the efforts of many other researchers, Gould said, "no one has been able to replicate his finding. I don't think it was real."
The potential link between the magnetite particles and cancer caused by electromagnetic fields is very tenuous also. "In the past, physicists have not believed in the link because they said there was nothing in the body affected by magnetic fields," Kirschvink said. "Now we have something."
"This is a provocative and interesting conclusion . . . but it is a mistake to say that we now understand how electromagnetic fields produce human health effects," countered Leonard Sagan of the Electric Power Research Institute in Palo Alto.
Sagan noted that it is difficult to envision a pathway by which the interaction of the particles and an electromagnetic field could cause cancer. Kirschvink conceded that he has not discovered a convincing scenario for such a link.
Nonetheless, said Frankel, "the discovery is very interesting for its own sake." When Kirschvink has determined where the particles are in the brain, he added, "then we can begin thinking about what they do."