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As the most common cause of progressive cognitive decline in humans, Alzheimer's disease (AD) has been intensively studied, but the mechanisms underlying its profound synaptic dysfunction remain unclear. Here we confirm that exposing wild-type mice to an enriched environment (EE) facilitates signaling in the hippocampus that promotes long-term potentiation (LTP). Exposing the hippocampus of mice kept in standard housing to soluble Aβ oligomers impairs LTP, but EE can fully prevent this. Mechanistically, the key molecular features of the EE benefit are an upregulation of miRNA-132 and an inhibition of histone deacetylase (HDAC) signaling. Specifically, soluble Aβ oligomers decreased miR-132 expression and increased HDAC3 levels in cultured primary neurons. Further, we provide evidence that HDAC3 is a direct target of miR-132. Overexpressing miR-132 or injecting an HDAC3 inhibitor into mice in standard housing mimics the benefits of EE in enhancing hippocampal LTP and preventing hippocampal impairment by Aβ oligomers in vivo. We conclude that EE enhances hippocampal synaptic plasticity by upregulating miRNA-132 and reducing HDAC3 signaling in a way that counteracts the synaptotoxicity of human Aβ oligomers. Our findings provide a rationale for prolonged exposure to cognitive novelty and/or epigenetic modulation to lessen the progressive effects of Aβ accumulation during human brain aging.