PER2 and memory impairment: Further, we used lentiviral vectors expressing shRNA to downregulate Per2 expression and found that DA-JC1 could no longer improve the learning and memory impairment of mice induced by Aβ31–35 after silencing of Per2 expression, indicating that Per2 in the hippocampus was involved in DA-JC1’s improvement of Aβ31–35-induced learning and memory impairment in mice.