PPIB and Cognitive impairment: Human postmortem studies have shown that while soluble Aβ oligomers and the density of neurofibrillary tangles strongly correlate with neurodegeneration and cognitive deficits, the density of Aβ insoluble plaques does not [20-24] and Αβ burden as assessed by PET does not strongly correlate with cognitive impairment in AD patients [25,26].