Valdez-Jimenez, et al. describe studies that show fluoride induces changes in the brain's physical structure and biochemistry which affects the neurological  and mental development of individuals including cognitive processes, such as learning and memory.  "Fluoride is capable of crossing the blood-brain barrier, which may cause biochemical and functional changes in the nervous system during pregnancy, since the fluoride accumulates in brain tissue before birth," they write.*  Animal studies show fluoride's toxic brain effects include classic brain abnormalities found in patients with Alzheimer's disease, Valdez-Jimenez's team reports.