became seriously ill after eating contaminated mussels. Several died; those who recovered sustained a major loss of memory. Brain scans from some of the victims showed an overwhelming loss of neurons from the hippocampus, similar to the pathology of the substantia nigra (a region involved in the control of movement) seen in Parkinson 's disease. The toxin from the mussels proved to be similar to glutamic acid, an excitatory neurotransmitter that occurs naturally in the central nervous system; it was also both highly potent and specific for those regions of the brain that process new memories. Such a substance is under study as a possible agent of Alzheimer's disease, as is the hypothesis that the disorder may be caused by a slow virus. Experimental testing of the virus theory would have to include a demonstrated ability to bring about recognizable “dementia” in laboratory animals solely by infection with the viral agent. Early claims of infection-induced dementia from one laboratory have not yet been replicated, despite attempts by the original group and a number of other research teams.

The theory that the presence of metal in the brain—specifically, aluminum—produces a toxic effect attracted lively interest when it was first advanced in the early 1970s. Evidence of aluminum in the neural tangles was plentiful and striking, and the theory circulated widely, to the point that the public began to wonder about the prudence of using aluminum cookware, for example. However, in the absence of evidence that further supports this theory or suggests how aluminum may work its harmful effects, the metal has lost some of its prominence as a possible cause of Alzheimer's. A current interpretation proposes instead that the aluminum in neural tangles may be a secondary effect, whose role (if any) in the development of this disease is unclear. Aluminum is, after all, an abundant element on earth, occurring naturally in water, soil, and much of our plant and animal food. Its presence in the brain may actually be the result of cells dying, rather than the cause; but this point is still under debate.

Vascular disease may figure in the onset of some dementias. The hippocampus is known to be an area of the brain that is highly susceptible to changes in blood flow; thus, some disruption of vascular function is being considered as at least a



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