4.1. Participants and ethics

The study included patients with cognitive decline complaints from the Memory Specialist Clinic of the Department of Neurology at Tongji Hospital, Tongji University. Ethical approval was granted by the Ethics Committee of Tongji Hospital, Shanghai, China. All participants provided informed consent. Patients were eligible for the study if they met the following criteria: (1) age over 50 years with no gender restriction; (2) absence of brain tumor, epilepsy, neurosyphilis, new cerebral infarction at the time of consultation, or other central nervous system diseases (infections, clear history of demyelinating diseases, etc.); (3) no significant physical medical conditions, such as hepatic encephalopathy or myocardial infarction; (4) no previous history of serious mental disorders, psychoactive substance or drug abuse; (5) able to cooperate with the examination, complete the full neuropsychological assessment, and sign an informed consent form; and (6) no contraindications to cranial MRI or EEG. A total of 82 patients were enrolled.

Based on the inclusion and exclusion criteria shown in Figure 5, a total of 82 participants completed EEG data collection. They were grouped according to their Aβ42/Aβ40 ratio. The positive group (Aβ42/Aβ40 ≤ 0.1) included 47 individuals with an average age of 71.62 ± 9.85, while the negative group (Aβ42/Aβ40 > 0.1) comprised 35 individuals with an average age of 69.34 ± 7.72. Cognitive assessments were conducted for both groups according to the 2011 NIA‐AA diagnostic criteria. The results are as follows: In the Aβ42/Aβ40 > 0.1 group, there were 15 participants with MCI and 20 participants with dementia. In the Aβ42/Aβ40 ≤ 0.1 group, there were 4 MCI participants and 43 dementia participants. A total of 77 participants completed both EEG and MRI scans. In the positive group (Aβ42/Aβ40 ≤ 0.1), there were 44 individuals with an average age of 71.45 ± 9.91, including four MCI and 40 dementia participants. In the negative group (Aβ42/Aβ40 > 0.1), there were 33 individuals with an average age of 69.24 ± 7.84, including 14 MCI and 19 dementia participants.