The aim of this study was an attempt to confirm the results of Lai et al. (1994), who reported that exposure to 2450 MHz radiation affected the spatial memory of rats and that this effect could be reversed by physostigmine.
Cobb and colleagues used the Lai et al. exposure frequency, pulsing regime and exposure device, exposure duration, and testing regime, and a radial arm maze (RAM) of the same configuration. They took special care to ensure that the experiment was conducted in a double blind fashion. Rats were exposed to pulsed 2450 MHz radiation or sham exposure for 45 minutes per day for 10 days, after a 4-day habituation period. The average whole body SAR was 0.6 W/kg. The animals received a pre-exposure injection of one of three psychoactive drugs (physostigmine, naltrexone hydrochloride, naloxone methodide) or saline. Following exposure, the rats, which had been on a restricted diet, were tested in a 12 arm, radial arm maze (RAM), in which they were expected to find a food pellet at the end of each arm. An error was scored if the animal entered the same arm more than once.
Analyses of error rates showed no significant exposure effect or drug effect. The rats showed improvement in their performance during the course of the 10 days. The rats injected with either physostigmine or naltrexone hydrochloride took significantly longer to complete their task than those treated with naloxone methodide or saline. There was no significant exposure effect on the time it took the animals to complete the task.
The authors pointed out that the dose of physostigmine they used (1 mg/kg) was the same as that used by Lai et al., but that this is considered to be a high dose. In fact some of the rats injected with this drug had seizures, and some died. Cobb et al. state that Lai et al. "did not report any incapacitation of any rats following administration of any of these psychoactive compounds".
There were minor changes in the protocol. Dustless precision pellets were used in the maze (to ensure no food residue was left behind after a rat had entered that arm) and no wood was used in the construction of the RAM (because rats tend to chew wood and this could affect the results).
The authors conclude "that there is no evidence from the current study that exposure to microwave radiation under parameters examined caused decrements in the ability of rats to learn the spatial memory task".