Participants
From April 2018 to November 2019, 33 individuals with aMCI and 32 age- and sex-matched healthy controls (HCs) with no physical diseases or history of psychiatric or neurological disorders were recruited from the local community to participate in this study through advertising. All participants ranged in age from 60 to 80 years, and each subject was a right-handed Han Chinese individual with normal who provided written informed consent for inclusion before this study began. The study was approved by the Ethics Committee of the Wuxi Mental Health Center of Jiangsu Province. The diagnosis of aMCI was determined by the consensus of all experienced neurologists according to the published criteria in the study by Petersen[24] and the National Institute on Aging-Alzheimer’s Association.
Inclusion and exclusion criteria
All participants underwent a broad battery of neuropsychological tests: (a) Hachinski score (HIS) to exclude objects with vascular dementia; (b) activities of daily living (ADL) scale to assess the subjects’ daily living abilities, including basic daily living abilities and relatively complex instrumental activities related to daily living; (c) Hamilton depression scale (HAMD) to exclude patients with a cognitive impairment caused by depression; and (d) Alzheimer’s disease assessment scale (ADAS-Cog) to assess the severity of cognitive impairment. All subjects were right-handed.
Inclusion criteria for the aMCI group are described below. According to the diagnostic criteria of Petersen: (i) memory complaint, preferably corroborated by an informant; (ii) objective memory impairment for age; (iii) relatively preserved general cognition for age; (iv) essentially intact activities of daily living; (v) no diagnosis of dementia. The following cutoff values were established for the neuropsychiatric tests described above: (1) HIS<4; (2) 14≤ADL≤19; (3) HAMD<16; (4) 10<ADAS-Cog<16, and (5) MoCA-B<26.
The normal participants were included based on the following criteria: (1) HIS<4; (2) 14≤ADL<16; (3) HAMD <16; and (4) ADAS-Cog<10, MoCA-B≥26. The exclusion criteria for both groups were an age <60 years and a history of psychiatric, neurological, cerebrovascular, or cognitive illness, stroke or other dementia diagnoses to ensure that they were cognitively normal.
Neuropsychological assessment
All subjects underwent clinical interviews, laboratory examinations, and activities of daily living (ADL) tests to assess functional impairment, and the ADAS-Cog was used to assess the severity of cognitive impairment. The Hamilton depression scale (HAMD) was used to exclude patients with a cognitive impairment caused by depression, and the Hachinski ischemic scale (HIS) was used to exclude people with vascular dementia.
MRI Data Acquisition
An MRI examination of participants was performed with a 3.0 T scanner (General Electric Medical Systems, 750 W, America) using a standard eight-channel phased-array head coil to obtain whole brain images of each subject. For the resting-state scan, the heads of all subjects were fixed with sponge padding and subjects were instructed to rest with their eyes closed, not fall asleep, think of nothing particular during the scan time, and continue to breathe normally during scanning. A structural T1-weighted image was acquired using a 3D SPGR sequence with the following parameters: repetition time (TR)=7.7 ms, echo time (TE)=minimum value, flip angle (FA)=11°, field of view (FOV)=256×256 mm2, matrix=256×256, slices=186, slice thickness=1.2 mm, and voxel size of 1×1×1 mm3. Functional data were collected using a gradient-echo echo-planar imaging (EPI) sequence in axial slices parallel to the line through the anterior and posterior commissures with the following parameters: TR=2 s, TE=30 ms, FA=90°, FOV= 224×224 mm2, matrix=64×64, slices=36, slice thickness =3.5 mm, gap=0.7 mm, voxel size of 3.5×3.5×3.5 mm3. The scan lasted for 240 s .
Statistical analyses
Demographic data were analyzed with IBM SPSS software version 26.0. The distributions of continuous variables approximated normality, and thus parametric tests were used. Two-sample t-tests were performed to examine the differences in age and education, while the chi-square test was used to analyze differences in sex. Two-sample t-tests were also used to compare neuropsychological test scale scores, including the HIS score and ADAS-Cog score, MoCA-B score, and the Mann–Whitney U test was used to examine the differences in HAMD scores. The average FC values of brain regions with distinct FC.
Functional connectivity analyses
Resting-state fMRI data from all participants were preprocessed using the Brainnetome fMRI Toolkit (http://brant.brainnetome.org) based on Statistical Parametric Mapping (SPM12, http://www.fil.ion.ucl.ac.uk/spm) and DPARSFA software using the MATLAB2018b platform (MathWorks). Before preprocessing, the first 10 time points were discarded because of the instability of the initial signal and the participant’s adaptation to the situation. All preprocessing steps included (1) slice-timing correction; (2) realignment to the first volume for head motion correction; (3) spatial normalization to a standard EPI template with reslicing to 2 mm cubic voxels; (4) discarding the effects of head motion and other possible sources of artifacts, such as linear drift, six motion parameters, and the mean time series of all voxels within the white matter and cerebrospinal fluid, to further reduce the effects of confounding factors; and (5) temporal filtering (0.01‒0.08 Hz) to reduce the effect of low-frequency and high-frequency noise. A head motion of <2 mm and rotation of < 2.0° were set as thresholds for each subject to minimize head motions. Three spherical regions of interest (ROIs) (radius=6 mm) were centered at the specified coordinates within the hippocampus (-24, -38, -2), thalamus (-36, 30, -14), and amygdala (2, 6, 1) [25].