This study aims to evaluate the safety and preliminary efficacy of combined auditory and visual 40-Hz stimulation in participants with biomarker-confirmed Alzheimer's disease spectrum disorders. A total of 60 participants with mild cognitive impairment due to Alzheimer's disease or mild Alzheimer's disease dementia will be randomly assigned in a 1:1 ratio to receive either active multisensory 40-Hz stimulation or sham stimulation. The intervention will be administered for 60 minutes once daily for 4 consecutive weeks. Clinical assessments, electroencephalography, multimodal magnetic resonance imaging, and blood biomarkers will be evaluated before and after the intervention. Additional clinical, electroencephalographic, and blood biomarker assessments will be performed at 3 and 6 months after the intervention.