Alzheimer's disease (AD) manifests itself in cognitive decline, impaired ability to perform daily life, and a variety of behavioral and psychiatric symptoms, seriously endangering the health of the elderly. The prevalence and disability rates of AD in China remain high, and the lack of effective treatment options has brought a heavy burden to patients and their families. Early intervention is regarded as an effective strategy to improve clinical symptoms, delay disease progression and maintain current quality of life. The humanized monoclonal antibody lencanemab (Lecanemab) was approved by the U.S. FDA in July 2023 for the treatment of mild cognitive impairment or mild dementia caused by AD, and was officially approved in January 2024 in China. Lencanemab highly targets soluble and insoluble neurotoxic β-amyloid (Aβ) proteins, reducing pathogenic Aβ plaque deposition and preventing its formation in the brains of AD patients, thus reducing neurotoxicity and improving patients' cognitive functions. In addition, lencanumab may also play a neuroprotective role by modulating synaptic plasticity and regulating neural network activity in brain neurons. However, there is a lack of clinical studies to prove this mechanism. In this study, we will enroll consecutive patients with early AD treated with lencanemab infusion as well as those receiving conventional anti-dementia therapy, and comprehensively assess the effects and intrinsic molecular mechanisms of lencanemab on synaptic function and neural networks using magnetic resonance imaging, molecular imaging positron emission tomography (PET), neuropsychological assessment, and analysis of blood cerebrospinal fluid samples.