In neuropsychiatric tradition, Alzheimer's disease (AD) is a clinical diagnosis that requires demonstration of a progressive memory-predominant type of dementia and exclusion of alternative causes. This simple set of criteria is neither sensitive for early clinical stages of AD since amnestic dementia only arises when the underlying neurodegeneration is fairly advanced, nor is it specific because it also occurs in other brain disorders involving the medial temporal lobe and cannot be easily distinguished from AD on clinical grounds. Efforts to identify AD before full-blown amnestic dementia develops, i.e. at a prodromal or even asymptomatic stage, and to treat the driving components of the pathology rather than its end products, are fueling the search for diagnostic indicators that unveil the neurodegeneration independently of its typical clinical manifestation. Such indicators are termed biomarkers in current technical parlance.