This study is affiliated to Sino Longitudinal Study on Cognitive Decline, SILCODE. To establish models of normal and pathological cognitive aging.To collect the longitudinal data of SCD population, to study the dynamic changes of brain networks so as to explore the progressive mechanisms of AD on brain networks and to construct a high-precision multi-modal model for early diagnosis.

This study is affiliated to Sino Longitudinal Study on Cognitive Decline, SILCODE. Alzheimer's disease (AD) is the most common cause of dementia, which severely injures multiple domains of cognitive functions in the aging people, bringing heavy burden to the society and families. Studying the cognitive brain damage mechanism of subjective cognitive decline (SCD), the preclinical stage of AD, would provide great opportunities for understanding the pathogenesis of AD and clinical value for early diagnosis and intervention in AD. The project intends to utilize amyloid-PET and FDG-PET for screening and then employ the comprehensive neuropsychological examination combined with multi-modal MRI neuroimaging techniques to study the brain functions and structures of the normal aging and SCD. The imaging data would be analyzed from several levels, including the cognitive dimensions, brain activation patterns, and especially functional and structural networks to establish the models of normal and pathological cognitive aging, which mainly be modulated by frontal-parietal control system. We aim to establish models of normal and pathological cognitive aging. Furthermore, the longitudinal data of SCD population would be collected to study the dynamic changes of brain networks so as to explore the progressive mechanisms of AD on brain networks and to construct a high-precision multi-modal model for early diagnosis

1. NC Inclusion Criteria:

1. Older than 60, right handedness, Han nationality;
2. Have no cognitive decline complains, with neither worry nor concern about their cognition;
3. Scores of standardized neuropsychological tests scale adjusted for age, sex and education are in normal range;
4. Physical examination is negative;
5. Review medical history and family history is negative, accessory examination don't show disease could cause cognitive decline;
6. Could cooperate collection of multi-modal magnetic resonance imaging, once a year, for continueously five years.

2. SCD Inclusion Criteria:

1. Presence of self-perceived continuous cognitive decline compared to previous normal status and unrelated to an acute event;
2. Failure to meet the following criteria for MCI.

3.SCD-plus Inclusion Criteria:

1. Presence of self-perceived continuous cognitive decline compared to previous normal status and unrelated to an acute event;
2. Concerns (worries) associated with memory complaint;
3. Failure to meet the following criteria for MCI.

3. MCI Inclusion Criteria:

1. Clinical Dementia Rating (CDR) score of 0.5 as well as failure to meet the criteria for dementia
2. Having impaired scores (defined as >1 SD below the age-corrected normative mean) on both measures within at least one cognitive domain (i.e., memory, language, or speed/executive function);
3. Having impaired scores in each of the three cognitive domains sampled;
4. the Functional Activities Questionnaire (FAQ) ≥9.

4. AD Inclusion Criteria The diagnosis of AD syndrome is based on the diagnostic guidelines for dementia due to AD delivered by the National Institute on Aging-Alzheimer's Association workgroups (NIA-AA)with a total CDR score of 1.

Exclusion Criteria:

1. Claustrophobia, with metals in the body that cannot be examined by MRI, including metal dentures or other contraindications for examination;
2. Left handedness or ambidextrality.

Volunteers recrewed from communities, and signed up with informed consent.