This study evaluates the effects of 3 years-Tai Chi exercise intervention on cognitive function in subjects with subjective cognitive impairment (SCI). Participants will be randomized into the Tai chi training group and the control group.

Dementia is a syndrome of impairments of cortical functions caused by brain diseases. More than 55 million people worldwide are currently living with dementia, with nearly 10 million new cases each year. Alzheimer's disease (AD) is the most common form of dementia and may account for 60-70% of patients with dementia. Mild cognitive impairment (MCI) is an intermediate state between normal cognitive aging and dementia. About 10% to 15% of patients with MCI progress to dementia each year. In recent years, studies have found that there is an earlier stage before MCI, that is, the stage of subjective cognitive impairment (SCI). SCI is a stage between normal aging and MCI, which is manifested by the self-reported experience of worsening or more frequent memory loss but not supported by objective evidence. Subjects with SCI are more likely to develop AD. According to the US CDC data, the prevalence of SCI among adults aged 65 years and older is 11.7%. Therefore, it is crucial to find intervention strategies to prevent the progression of SCI to MCI and dementia. However, drug interventions are currently ineffective in the prevention and treatment of such diseases. Based on the synaptic plasticity, more and more studies focus on non-drug interventions. Our research group previously found non-drug interventions (cognitive training, exercise therapy) can effectively delay cognitive decline in the elderly. Therefore, this project plans to conduct a multi-site, randomized, parallel-controlled clinical trial to examine the effect of 3 years-Tai Chi exercise intervention on cognitive function in SCI subjects and to provide a new clinical basis for the prevention and treatment of cognitive disorders.

Inclusion Criteria:

1. Male and female participants aged 60 to 75 years (inclusive) at the time of screening;

2. Willing and able to give informed consent by GCP and local guidance;

3. Meets the diagnostic criteria for subjective cognitive impairment (SCI) and the following criteria

   • Subjective decline in memory, rather than other domains of cognition
   • Onset of SCI within the last 5 y
   • Concerns (worries) associated with SCI
   • Feeling of worse performance than others of the same age group
   • Confirmation of cognitive decline by an informant.

4. Have the physical, cognitive, listening, speech, literacy and language skills necessary to participate in all tests;

5. Capable of performing MR.

Exclusion Criteria:

1. Cognitive impairment caused by other reasons (for example) cerebrovascular disease, central nervous system infection, Creutzfeldt-Jakob disease, Huntington's disease, Parkinson's disease, dementia with Lewy bodies, trauma, other physical and chemical factors (drugs, alcohol, CO, etc.), important physical diseases (hepatic encephalopathy, pulmonary encephalopathy, etc.), brain tumor, endocrine diseases (thyroid disease, parathyroid disease), and vitamin deficiency or any other cause of dementia;

2. Abnormal folate, thyroid, and/or vitamin B12 values that cannot be corrected before baseline visit;

3. Major structural brain disease as judged by central MRI Diagnostic Imaging Review Team (eg, ischemic infarcts, subdural hematoma, hemorrhage, hydrocephalus, brain tumors, multiple subcortical ischemic lesions. or a single lesion in a critical region [eg, thalamus]). Mild white matter changes without clinical significance and no more than 2 lacunar infarcts are permitted;

4. Geriatric Depression Scale-15(GDS-15) total score > 7 at screening;

5. MOCA<26 points;

6. CDR global score >0;

7. Hachinski ischemia score >4;

8. During the clinical study, the following drugs are prohibited:

   Acetylcholinesterase inhibitors, N-methyl-D-aspartate (NMDA) antagonists (eg, memantine), central nervous system stimulants, and various medicines that can improve memory or cognition; Antipsychotics

9. Mental illness determined by Diagnostic and Statistical Manual of Mental Disorders (DSM) V criteria, that is unstable within 12 months, or would interfere with study assessments, including schizophrenia or other psychotic disorders, bipolar disorder, severe depression, or delirium.

10. DSM V diagnosis of alcohol or other substance abuse dependence within the last 12 months.

11. History or current diagnosis of significant cardiac arrhythmias, myocardial infarction, transient ischemic attack, or cerebrovascular accident, uncompensated congestive heart failure New York Heart Association class III and IV.

12. Major medical illness or unstable medical condition within 6 months of screening that in the opinion of the investigator may interfere with the participant's ability to comply with study procedures and abide by study restrictions, or with the ability to interpret safety data, including any physical disability (eg. blindness. deafness, non-cognitive related speech impairment, sensory or motor dysfunction) that would prevent completion of study procedures or assessments.

13. Cancer except:

    History of any cancer that has been in remission (no evidence of recurrence) for > 5 years from the screening Participants with basal cell or stage I squamous cell carcinoma of the skin, stable untreated cancer as prostate or meningioma.

14. Active physical activity for 6 months prior to screening.

15. Participants are excluded if they

    1. have participated in any other clinical study within 4 weeks prior to screening visit
    2. have participated in another Tai chi clinical study at any time
    3. plan to take part in another clinical study during this study.

16. The researcher estimates that the subject's compliance is poor, and it is believed that the subject is unlikely to complete the study.