As populations age, Alzheimer's disease (AD) is increasing while disease-modifying drugs remain elusive, making early diagnosis and intervention essential. Building on advances in neuromodulation and virtual reality (VR), we target amnestic mild cognitive impairment (aMCI)-the prodromal stage of AD-as a key window for prevention. Preliminary evidence shows disrupted theta-delta phase-amplitude coupling in prefrontal and temporal cortices in aMCI, whereas olfactory enrichment can enhance hippocampal synaptic function, improve cognition, and potentially lower AD risk. We will conduct a large-scale clinical cohort study to test the neural mechanisms and clinical efficacy of multi-site, cross-frequency transcranial alternating current stimulation (tACS) combined with multisensory (visual-olfactory-auditory) VR. A comprehensive database spanning demographic, neuropsychological, biochemical, neuroimaging, and neuromodulation parameters will guide optimal protocols and provide objective evidence for non-pharmacological interventions, informing development of a microcurrent brain stimulator and a portable VR device.