Some scientists in China did some research from which they concluded that fluorides may be causing some cases of birth defects. Scientists in America are acustomed to doing their own research. In 1995, group of scientists from four medical research institutes in the United States published their findings in Neurotoxicology and Teratology, Volume 17, No.2, pp. 169-177, under the title, "Neurotoxicity of Sodium Fluoride in Rats."
Everybody knows that fluorides have something to do with minerals in bones, but no one had done a first class investigation into what fluorides might do to the brain. Could exposure to sodium fluoride cause damage to the nervous system directly and could it do this before it caused the physical deformations of skeletal fluorosis? An important finding in this experiment was that it's the amount of fluorides in the blood that is most relevant to the potential for damage to the brain rather than how much is in the water. People do occasionally have blood levels of fluoride like the ones in this rat experiment.
The experiment showed that sodium fluoride can interfere with the function of the brain. Normally, the hippocampus region of rat brains has the least concentration of fluoride, but female rats who drank fluoridated water when they were very young had much higher concentrations of fluoride in the hippocampus than in any other part of the brain. Fluoride accumulates in the brain tissues. Hippocampal damage is generally linked with hyperactivity and cognitive deficits. The hippocampus is the "central processor which integrates input from the environment, memory, and motivational stimuli to produce behavioral decisions and modify memory." The authors are convinced that fluoride may interfere with the function of calcium in the hippocampus of females.
The timing of exposure to fluoride during the development of the central nervous system determines the kind of defect. Pre-natal exposure is likely to cause hyperactivity, but post-natal exposure is more likely to cause cognitive deficits. The male rats were more likely to have a defect of brain function if their mothers had an excessive exposure to sodium fluoride on certain days during pregnancy.
This was a carefully done experiment. The researchers used video cameras taking pictures at the rate of one frame per second during the testing of the rats' behavior and analyzed the pictures with a computer program. They concluded there is a potential for fluorides to cause some cases of motor dysfunction, less IQ than there would have been and learning disabilities in people.