The most frequent of the primary degenerative dementias is Alzheimer's disease (AD). The gradual loss of memory and attention in patients suffering from this illness are accompanied by aphasia, apraxia, agnosia, and alterations in visual-spatial perception. This group of symptoms is completed by emotional alterations, psychic instability, and changes in personality that appear in advanced phases of the illness. Different histopathological alterations have been described, like marked atrophy of the cerebral cortex with loss of cortical and subcortical neurons. Other histopathological hallmarks are the formation of senile plaques composed of beta-amyloid (Abeta) and neuro fibrillary tangles composed of hyperphosphorylation of tau protein.