The goal of this clinical trial is to learn about the effects of social isolation and social interaction on the risk of dementia progression and brain function in SCD 1. To explore the association between social isolation and lonely SCD populations and the occurrence and progression of MCI and AD through cross-sectional studies, cohort studies and randomized controlled trials of SCD; 2. To clarify the correlation between different carrier states, resting brain function connectivity characteristics, and dual-task walking ability of APOEε4 allele and the progression of SCD to MCI and AD during the cognitive progress of people with SCD affected by social isolation; 3. Establish a predictive model of cognitive decline from SCD to MCI and AD, and apply it to the SCD population to carry out individualized interventions; 4. Confirm the protective effect of social interaction on cognitive level and brain function in SCD patients.