Microwaves similar to those emitted by cell phones may affect long-term memory, according to a new study by a University of Washington researcher.

Henry Lai, a research professor in the UW's bioengineering department, has linked diminished long-term memory and navigating skills in rats with exposure to microwaves like those from cellular telephones.

According to Lai, this is the first study to link exposure to the radio waves to long-term memory function.

"Studies before this one have focused more on short-term memory," he said. "In this study, the long-term memory of microwave-exposed rats appears to have been affected."

Lai's findings are scheduled to be published in the January issue of the journal Bioelectromagnetics.

In the study, Lai placed rats in a large tank of water and trained them to swim to a submerged platform. Powdered milk, mixed into the water, ensured that the rats couldn't see the platform and had to memorize the way to it. The rats had one minute to find the platform. If they still hadn't found the platform by then, they were picked up and set on it. The animals were then reintroduced into the pool from a different location to repeat the process. Each rat was allowed four attempts to locate the platform during each of the six training sessions the animals received. A total of 100 rats went through the process.

The repetition allowed the rats to store the task of locating the ramp in their long-term memories, according to Lai. Long-term memory deals with items that have been learned or recalled and stored in the brain, he explained, as opposed to short-term memory, which has to do with tasks one has just performed or information one has just looked at.

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Before each training session, rats from one group were exposed for one hour to pulsed microwaves, radiation similar to that emitted by cellular telephones. Lai noted that the learning process itself appeared to have been affected by the exposure. A control group was not exposed.

"The microwave-exposed rats were much slower in finding the platform during the training sessions," Lai said. "They tended to spend more time attempting to climb the wall of the pool or swimming along the wall." The swimming speed of all the rats remained the same, however, which indicated that the difference didn't stem from a change in motor skills or motivation. The change appeared to be in learning prowess.

Researchers then removed the platform and watched what happened when the rats were put back into the pool.

The control group spent most of their time swimming in the area where the missing platform had been located. "They seemed to be scratching their heads, saying 'We thought it was here,'" Lai said.

But the irradiated rats behaved more randomly, spending more time swimming in other parts of the pool and showing much less of a tendency to search for the platform.

"They seemed to have trouble making a map in their heads, like the normal rats did, so they could recall where the platform was," Lai said. "Their spatial reference mapping or 'place learning' strategies seemed to be affected after their exposure. It could be that they had to resort to a simpler learning strategy that just didn't work as well and they couldn't remember how to find the platform."