There is compelling evidence supporting amyloid as one of the key pathologic agents in AD. Autopsy studies suggest the amount and location of fibrillar amyloid deposition does not relate strongly to the degree and type of clinical impairment, compared to tau pathology and neuronal loss. A substantial percentage of individuals known to be cognitively intact prior to death demonstrate significant amyloid pathology at autopsy. PIB-PET studies of older normal individuals have also demonstrated significant amyloid deposition in substantial percentages.