MAPT and Alzheimer disease: Well-characterized Aβ1-42 species, such as oligomers, protofibrils, and fibrils, should be administered to induce a significant decrease in memory and an impairment of synaptic plasticity, a decreased number of viable neurons, increased tau levels, and a decreased number of dendritic spines; at this point researchers would have a well-established rat AD model [71].