Effect of Lifetime Cognitive Reserve on Functional Connectivity in the Default Mode Network at the Predementia Stage

Objective@#Cognitive reserve (CR) protects against cognitive decline by utilizing functional connectivity (FC) in the brain, such as the default mode network (DMN). We studied whether CR in individuals with predementia would correlate with better cognition and increased DMN FC in the resting brain. @*Methods@#Fifty-four participants with subjective cognitive decline or mild cognitive impairment completed the Cognitive Reserve Index (CRI) questionnaire, and underwent a comprehensive neuropsychological test battery and resting state functional magnetic resonance imaging. Correlation and regression analyses for clinical variables and seed-to-voxel analyses of CR-related FC in the DMN were conducted. @*Results@#CRI total (β=0.42, p=0.001), education (β=0.39, p=0.001), and leisure time (β=0.33, p=0.009) predicted the MiniMental State Examination. The CRI education predicted verbal memory recall (β=0.32, p=0.017), confrontational naming (β=0.57, p<0.001), and phonemic fluency (β=0.43, p=0.004). In the DMN in the resting brain, the CRI total correlated with increased FC, based on the posterior cingulate to both lateral parietal cortices. @*Conclusion@#In individuals with predementia, comprehensive CR correlated with an enhanced network in the DMN in the resting state. These results may support the neural correlate of CR during the initial stage of cognitive decline.

Usefulness of the Clock Drawing Test as a Cognitive Screening Instrument for Mild Cognitive Impairment and Mild Dementia: an Evaluation Using Three Scoring Systems

BACKGROUND AND PURPOSE: Although the clock drawing test (CDT) is a widely used cognitive screening instrument, there have been inconsistent findings regarding its utility with various scoring systems in patients with mild cognitive impairment (MCI) or dementia. The present study aimed to identify whether patients with MCI or dementia exhibited impairment on the CDT using three different scoring systems, and to determine which scoring system is more useful for detecting MCI and mild dementia. METHODS: Patients with amnestic mild cognitive impairment (aMCI), vascular mild cognitive impairment (VaMCI), mild Alzheimer's disease (AD), mild vascular dementia (VaD), and cognitively normal older adults (CN) were included. All participants were administered the CDT, the Korean-Mini Mental State Examination (K-MMSE), and the Clinical Dementia Rating scale. The CDT was scored using the 3-, 5-, and 15-point scoring systems. RESULTS: On all three scoring systems, all patient groups demonstrated significantly lower scores than the CN. However, while there were no significant differences among patients with aMCI, VaMCI, and AD, those with VaD exhibited the lowest scores. Area under the Receiver Operating Characteristic curves revealed that the three CDT scoring systems were comparable with the K-MMSE in differentiating aMCI, VaMCI, and VaD from CN. In differentiating AD from CN, however, the CDT using the 15-point scoring system demonstrated the most comparable discriminability with K-MMSE. CONCLUSIONS: The results demonstrated that the CDT is a useful cognitive screening tool that is comparable with the Mini-Mental State Examination, and that simple CDT scoring systems are sufficient for differentiating patients with MCI and mild dementia from CN.

Disproportionate Decline of Executive Functions in Early Mild Cognitive Impairment, Late Mild Cognitive Impairment, and Mild Alzheimer's Disease

BACKGROUND AND PURPOSE: Many literatures indicate that executive dysfunction exists in mild cognitive impairment (MCI) as well as Alzheimer’s disease (AD). However, there are few studies that found how early the deficits of the executive function (EF) exist in MCI. The present study investigated the presence of executive dysfunctions in the earliest stage of MCI, and the sub-domains of EF which are disproportionately impaired earlier than others. METHODS: The participants were 41 normal elderly (NE), 86 with amnestic multi-domain MCI, and 41 with mild AD. The MCI group was further sub-divided into two groups: Early MCI (EMCI, n=45) and late MCI (n=41), based on the Clinical Dementia Rating-Sum of Boxes. All participants were given neuropsychological tests to assess the sub-domains of EF, such as verbal fluency, psychomotor speed, inhibitory control, and mental set-shifting. RESULTS: Impairment of semantic fluency was observed in EMCI, with gradual worsening as cases approached mild AD. Phonemic fluency and psychomotor speed were also impaired at the early stage of MCI relative to the NE, but maintained at the same level up to mild AD. EMCI exhibited the same degree of performance with NE for inhibitory control and mental set-shifting; however, they progressively worsened from EMCI to mild AD. CONCLUSIONS: These results suggest that impairments of EF exist even in the earliest stage of the MCI, with a disproportionate decline in the sub-domains of EF.