Participants receive 40Hz combined audio-visual stimulation (visual + auditory) for 60 minutes per day, once daily, for 6 consecutive months. In addition, the device performs EEG acquisition and closed-loop feedback adjustment based on preset algorithms. This allows individualized, closed-loop neuromodulation.

Participants receive sham stimulation using a device identical in appearance and weight to the active device. The sham device does not output effective individualized audio-visual stimulation; only low-intensity, randomized flashes and audio cues are delivered.

The STT is a validated neuropsychological test assessing executive function, attention, and psychomotor speed. STT-A primarily measures processing speed, while STT-B measures executive function and task-switching ability. Lower completion time indicates better performance. Assessments will be performed by trained neuropsychologists blinded to group assignment.

The DST is a validated neuropsychological test assessing working memory and attention. The test includes forward digit span (attention) and backward digit span (working memory). Higher scores indicate better working memory performance. Assessments will be performed by trained neuropsychologists blinded to group assignment.

Changes in structural brain imaging parameters will be assessed using 3T MRI, including gray matter volume, cortical thickness, and hippocampal volume. These parameters will be used to evaluate the neuroprotective effects of the intervention. Imaging data will be analyzed by neuroradiologists blinded to group assignment.

Changes in functional brain connectivity will be assessed using resting-state fMRI. Key parameters include functional connectivity within the default mode network (DMN) and gamma-band related networks. Imaging data will be analyzed by neuroradiologists blinded to group assignment.

Changes in peripheral blood biomarkers associated with Alzheimer's disease pathology will be assessed. Biomarkers include: (1) amyloid beta 42 (Aβ42); (2) amyloid beta 40 (Aβ40) and the Aβ42/Aβ40 ratio; (3) phosphorylated tau (p-Tau181 or p-Tau217); (4) total tau (t-Tau); (5) neurofilament light chain (NfL).

Changes in brain amyloid beta burden will be assessed using Aβ-PET imaging. The primary measure is the standardized uptake value ratio (SUVR) in predefined regions of interest (including frontal, temporal, parietal, and occipital cortices, as well as the precuneus and cingulate). Higher SUVR indicates greater amyloid burden. Imaging data will be analyzed by nuclear medicine physicians blinded to group assignment.

Changes in brain tau pathology will be assessed using tau-PET imaging. The primary measure is the standardized uptake value ratio (SUVR) in predefined regions of interest (including medial temporal lobe, temporal cortex, parietal cortex, and other Braak stage regions). Higher SUVR indicates greater tau burden. Imaging data will be analyzed by nuclear medicine physicians blinded to group assignment.

The incidence, severity, and causality of all serious adverse events (SAEs) will be assessed throughout the study period. SAEs include: death, life-threatening events, persistent or significant disability or incapacity, hospitalization or prolonged hospitalization, fetal distress, fetal death, congenital anomalies or birth defects, and any other important medical events that may jeopardize the patient or require intervention to prevent one of the above outcomes.

The incidence, severity, and causality of all adverse events (AEs) will be assessed throughout the study period. AEs include but are not limited to: transient dizziness, visual fatigue, headache, nausea, attention fluctuation, drowsiness, eye dryness, tinnitus, irritability, anxiety, and any other unexpected events. Severity will be graded as mild, moderate, or severe. Relationship to the intervention will be classified as: definitely related, possibly related, potentially related, possibly unrelated, or definitely unrelated.