Characterizing Global and Regional Brain Structures in Amnestic Mild Cognitive Impairment Among Rural Residents: A Population-Based Study

Study design and participants

This is a population-based case-control study. The study participants were derived from the Shandong Yanggu Study of Aging and Dementia that targeted people who were aged 65 years and older and living in the rural communities of Yanlou Town, Yanggu County, western Shandong Province, China. Briefly, the two-phase examination procedure was implemented in the study in August 2014-September 2015. At phase I (a screening phase, August-December 2014), 3,277 eligible participants underwent face-to-face interviews and clinical examination, during which the Mini-Mental State Examination (MMSE) and the Ascertain Dementia 8-item Questionnaire (AD8) were used to screen for global cognitive im-pairment. The MMSE score ≤24 or AD8 score ≥2 was considered screening positive [16, 17]. Then, a total of 1,981 participants who were positive in either screening test at phase I were eligible for phase II examination (a clinical phase) that included comprehensive clinical and neuropsychological ass-essments. From December 2014 to September 2015, 997 (50.3% of participants who were positive in either screening test at phase I) eventually accomplished the phase II assessment. Neuropsychological assessments at phase II included administration of the Auditory Verbal Learning Test (short-term delayed recall, long-term delayed recall, category-cued recall and recognition) for episodic memory, the Fuld Object Memory Evaluation, the Category Verbal Fluency test and the Boston Naming Test for language, the Trail Making Test and Stroop interference test for executive function, the Wechsler Memory Scale-III Forward Digit Span and Backward Digit Span for attention, the Wechsler block design test and the Clock Drawing Test for visuospatial ability, the Functional Activities Questionnaire (FAQ) for instrumental activities of daily living, the Hamilton Depression Rating Scale, and the Hachinski Ischemic Score.

Following the clinical phase, 217 individuals were invited and agreed to undertake brain MRI scan in November 2015-January 2016. Of these, 37 persons were excluded due to dementia (n = 12), non-aMCI (n = 2), vascular cognitive impairment (n = 1), uncertain diagnosis (n = 5), lack of T1-weighted images (n = 2) or brain infarcts on FLAIR and T2-weighted images (n = 17, 2 with dementia and 1 with uncertain diagnosis) that might affect the reliable assessment of brain tissue volumes, leaving 180 persons for the current analysis. Figure 1 shows the flowchart of the study participants.

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Fig. 1

Flowchart of the study participants. MMSE, Mini-Mental State Examination; AD8, Ascertain Dementia 8-item Questionnaire; MRI, magnetic resonance imaging; aMCI, amnestic mild cognitive impairment; VCI, vascular cognitive impairment.

The protocol of the Shandong Yanggu Study of Aging and Dementia was reviewed and approved by the Ethics Committee on Human Experimentation at Shandong Provincial Hospital affiliated to Shandong University in Jinan, Shandong. Written informed consents were obtained from all participants, or if the participants were not able to give the consent, from the informants.

Data collection and assessments

Trained medical staff collected data through face-to-face interviews and neuropsychological testing. Data included demographics (e.g., age, sex, and edu-cation), lifestyles (e.g., smoking, alcohol consumption, and physical exercise), health history (e.g., hypertension, diabetes, and high cholesterol level). We categorized education as illiterate, elementary school, and middle school or above, smoking and alcohol intake as ever versus never, and physical exercise as at least weekly versus less than weekly. We measured arterial blood pressure on the right upper arm in a seated position after a 5 min rest using an electronic blood pressure monitor. We defined hypertension as systolic pressure ≥140 mm Hg or diastolic pressure ≥90 mm Hg, or having the self-reported history of hypertension. We defined diabetes according to the self-reported history of diabetes diagnosed by a physician or fasting blood glucose ≥7.0 mmol/L. We defined hyperlipidemia as total serum cholesterol ≥6.2 mmol/L or triglyceride ≥2.3 mmol/L, or low-density lipoprotein cholesterol ≥4.1 mmol/L, or high-density lipoprotein cholesterol <1.0 mmol/L, or having a self-reported history of hyperlipidemia.

Following the phase II examination, senior neurologists specialized in dementia care and treatment made diagnosis of dementia according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, criteria (DSM-IV) [18], after reviewing all records from face-to-face interviews, clinical examination, and neuropsychological testing, as previously reported [19].

aMCI was defined by the two neurologists (L.C. and H.T.) via reviewing all records from the face-to-face interviews, clinical examination, and compre-hensive assessments of sub-cognitive domains, following the Petersen’s criteria [20]: 1) Memory complaint or concern corroborated by the subject or an informant, assessed by response to the question: “Do you have daily problems with thinking or memory”; 2) Objective memory impairment beyond normal aging, according to performance of memory test (Auditory Verbal Learning Test) and consensus agreement among the two neurologists; 3) Preserved global cognitive function assessed by the education-based MMSE score (MMSE score > 17 for illiteracy, >20 for elementary school, or >22 for middle school or above) [21]; 4) Normal functional activities assessed by FAQ (FAQ score <6) [19]; and 5) Absence of dementia according to the DSM-IV criteria [18].

MRI acquisition and imaging assessment protocols

All participants were scanned at one of the three MRI centers in Liaocheng, Shandong. The common core MRI protocol included the 3D T1-weighted, T2-weighted, and 3D fluid attenuated inversion re-covery (FLAIR) sequences. In the Liaocheng Third People’s Hospital (GE Healthcare-Signa 1.5T, USA), the parameters for the T1-weighted sequence were: repetition time (TR) = 10.12 ms, echo time (TE) = 3.25 ms, thickness = 1.20 mm, spatial resolution = 0.60×0.60×0.60 mm³. In the Liaocheng People’s Hospital (Philips-Achieva 3.0T, The Netherlands), the T1-weighted sequence parameters were: TR = 6.90 ms, TE = 3.20 ms, thickness = 1.10 mm, spatial resolution = 1.10×1.10×1.10 mm³. In the Liaoch-eng Brain Hospital (Siemens-Magnetom Avanto 1.5T, Germany), we used the following parameters: TR = 2400 ms, TE = 3.60 ms, thickness = 1.20 mm, spatial resolution = 1.30×1.30×1.20 mm³.

We used the 3D T1-weighted images to quantify the global and regional brain volumes. Global and regional brain volumes were segmented via the Computational Anatomy Toolbox (CAT12) in Matlab (http://dbm.neuro.uni-jena.de/cat12/). CAT12 used the a standard brain template of Montreal Neurolo-gical Institute to automatically normalize the skull-st-ripping brain, estimate the total intracranial volumes (ICV), and segment brain tissues into GM, WM, and CSF based on the Adaptive Maximum A Posteriori technique [22, 23], and automatically detect the WMHs. Then, we extracted the regional volumes of GM and WM according to the Hammers atlas for external analysis [24].

Statistical analysis

We compared the characteristics of study participants by aMCI status using nonparametric Kol-mogorov-Smirnov test for continuous variables and χ² tests for categorical variables. We used the gen-eral linear regression models to estimate β coefficient and 95% confidence interval of global measures of brain volumes (i.e., ICV, GM, WM, CSF, and WMH) associated with aMCI, in which we reported the main results from two models: model 1 was adjusted for age, sex, education, occupation, scan centers, and, if applicable, for ICV; model 2 was additionally adjusted for physical exercise, smoking, alcohol intake, hypertension, diabetes and hyperli-pidemia. Furthermore, we performed the full-fac-torial design model (masking threshold = 0.001) to compare the differences of voxel-based volumetric brain measures by aMCI status, while controlling for age, sex, education, occupation, ICV, MRI centers, physical exercise, smoking, alcohol intake, hypertension, diabetes, and hyperlipidemia. Then, we performed the ROI-based analysis to identify the brain regions with significant differences in voxel-based volumes between people with and without aMCI, in which the significance level was controlled for false discovery rate (FDR). Finally, for all significant group-difference brain regions, we employed multiple general linear regression models to further assess the volumetric differences between the two groups of persons with and without aMCI.

CAT12 Toolbox was used for both the full factorial design and the ROI-based analyses. Stata Statistical Software: Release 16 for Windows (StataCorp LLC., College Station, TX, USA) was used for the other statistical procedures.

Characteristics of study participants

The mean age of the 180 participants was 69.23 (3.73) years, 40% were female, and nearly two-thirds attended no formal school or only primary school. Compared to the normal controls, people with aMCI were more likely to be female and farmers, less educated, and were less likely to do physical exercise, smoke, and consume alcohol (p < 0.050). As expected, the aMCI group had a lower mean MMSE score and a higher mean AD8 score than the control group (p≤0.006). The two groups did not differ significantly in mean age and the distribution of MRI centers and chronic diseases (p > 0.050).

Global measures of brain structure

Compared to normal controls, people with aMCI had reduced volumes of total GM and total WM but higher volumes of CSF and WMH, even when controlling for multiple potential confounders (p < 0.005, Table 2). The two groups did not differ significantly in ICV.

Regional grey matter and white matter volumes

After controlling for multiple potential confou-nders, people with aMCI had significantly reduced GM volumes in the bilateral superior temporal reg-ions and thalamus, and right cuneus (FDR corrected p < 0.05, Table 3 and Fig. 2A).

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Fig. 2

Voxel-wise comparisons of regional grey matter and white matter volumes between people with and without amnestic mild cognitive impairment. Regional volumes were lower in the aMCI group (n = 42) compared with normal controls (n = 138) after controlling for age, sex, education, occupation, ever smoking, alcohol intake, physical exercise, hypertension, diabetes, hyperlipidemia, total intracranial volume, and MRI centers. A) Regional GM volume (e.g., bilateral temporal gyri and thalamus) was reduced in the aMCI group compared with normal controls after FDR correction. B) Regional WM volume (e.g., bilateral frontal and superior temporal areas) was reduced in the aMCI group compared with cognitively normal controls.

Compared to normal controls, the aMCI group had significantly lower WM volumes primarily in bilateral superior, middle, inferior and orbito-frontal areas, bilateral superior temporal gyri, posterior temporal lobes, inferior lateral parietal lobes, lateral occipital lobes, left lingual gyrus, bilateral precentral and right postcentral gyri, and right hippocampus in both the ROI-based analysis and the multiple-variable adjusted general linear regression analysis (FDR corrected p < 0.05, Table 3 and Fig. 2B).