Yamaguchi H, Tsurita G, Ueno S, Watanabe S, et al (2003):

This study sought to clarify the effects of exposure to electromagnetic fields (EMF) used in cell phones on learning and memory processes. Rats were exposed for either 1 hour daily for 4 days or for 4 weeks to a pulsed 1439 MHz TDMA field. At the brain, average SAR was 7.5 W/kg, and the whole body average was 1.7 W/kg. Other rats were exposed at the brain average of 25 W/kg and the whole body average of 5.7 W/kg for 45 minutes daily for 4 days. After habituation and training in a food rewarded T-maze, the rats were tested with the food in the opposite arm of the T-maze than had been used in the training period. The tests were done immediately after the EMF exposure in the 4 days experiment. In the 4 weeks experiment, the rats were exposed to EMF for 3 cycles of 5 days, each followed by 2 days' rest. After the third cycle (and 2 days' rest) the rats were tested in the next 4 days immediately after exposure for 1 hour daily. Sham-exposed rats and cage control rats were also tested. The intraperitoneal temperature of rats was tested for each exposure condition in a sample of 4 animals.

Rats exposed to the brain average SAR of 7.5 W/kg for either 4 days or 4 weeks showed no T-maze performance impairment. However, those exposed to a brain average SAR of 25 W/kg showed significant decreases in the number of correct choices in the T-maze. The intraperitoneal temperature of the rats exposed at SAR of 25 W/kg rose by 2°C, but was normal in rats exposed at a SAR of 7.5 W/kg.

The authors state that the results suggest that the exposure to a TDMA field at levels about four times stronger than that emitted by cell phones does not affect the learning and memory processes when there are no thermal effects. In the "Discussion" section of their paper the authors point out that their results differ from those of Wang and Lai (2000), and suggest that this might be due to differences in the exposure systems. They argue that the system used by Wang and Lai could produce the microwave hearing effect, thus influencing the rats' behaviour.

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