Tau oligomers impaired the recognition memory in mice. (A) Effects of tau oligomers, fibrils, and monomers on memory were investigated in C57BL/6 mice by using the object recognition task. Histograms indicate the percentage of exploration of the familiar and novel objects. Mice injected with monomers or fibrils spent significantly more time investigating the novel object versus mice injected with tau oligomers, indicating impaired memory, as shown by their inability to recognize the familiar object. #p < 0.01 vs. novel object. (B) Histograms show the corresponding discrimination index (mean ± SD) for the data shown in A. *p < 0.01. As a control, behavioral analyses were performed on mice without injection.