Recent research1 from NRPB shows that short-term, repeated exposure to intense magnetic fields may affect the behaviour of mice. In this study, mice were exposed each day to a 50 Hz magnetic field before being tested in a radial arm maze, a standard behavioural test of the ability of mice to learn a procedure for seeking food. Similar effects have been reported from studies with rats2.
It was found that exposure to intense fields, about 1000 times higher than those found in most houses, resulted in the mice making more errors in the maze leading to a reduction in the speed with which they learned to seek food. However the exposed animals eventually learned the task as well as unexposed control animals, suggesting that no permanent effects had occurred. It is possible that minute electric fields and currents induced in the brain by the magnetic field may have interfered in some fashion with the processing of spatial information, leading to the observed changes in behaviour. No specific mechanism for these effects has yet been identified.
These effects on behaviour do not occur under all conditions. In other experiments performed at NRPB, it was found that exposure was without effect if animals were exposed to weaker fields (although these were still much larger than those found in most houses) or only exposed for a short time during testing. Also the effects caused by the magnetic fields are only temporary and seem to "wear off" within an hour: the introduction of a delay between exposure and testing completely abolished the effects of the magnetic field. Results of other tests indicate that previous learning is unaffected, even by exposure at high field strengths.
The studies therefore show that if the magnetic fields are to cause an effect, the animals must be exposed to an intense field for about an hour and that learning a new task must start very soon after exposure. If the animals are exposed to a weak field or for a short time, no deficits are seen. The fields found in most homes are very much weaker than the fields used in this study.
While these studies are of considerable scientific interest in that they show a short-term, biological effect from exposure to magnetic fields, they do not suggest that exposure to everyday magnetic fields would have any adverse effect on people, for example, on children playing computer games for several hours each day.
Further research is planned to explore these effects in mice more fully.
First issued 4th July 1997
Last updated 13th February 1998