MAPT and Cognitive impairment: In this study, we evaluated the early time course of pathological changes associated with the expression of full-length human wild-type 4-repeat, 0-N-terminus tau isoform (tau4R) in the rat hippocampus utilizing AAV9 and evaluated tau-mediated neurodegeneration, including early- and late-stage phosphorylation species, and how these tau pathology changes might affect cognitive impairment associated with AD.