Abstract
Individuals with subjective cognitive decline (SCD) are more likely to develop into Alzheimer disease (AD) in the future. Resting-state functional magnetic resonance imaging (rs-fMRI) studies have shown alterations of intrinsic brain activity (IBA) in SCD individuals. However, rs-fMRI studies to date have mainly focused on static characteristics of IBA, with few studies reporting dynamics- and concordance-related changes in IBA indices in SCD individuals. To investigate these aberrant changes, a temporal dynamic analysis of rs-fMRI data was conducted on 94 SCD individuals (71.07 ± 6.18 years, 60 female), 75 (74.36 ± 8.42 years, 35 female) mild cognitive impairment (MCI) patients, and 82 age-, gender-, and education-matched controls (NCs; 73.88 ± 7.40 years, 49 female) from the Alzheimer's Disease Neuroimaging Initiative database. The dynamics and concordance of the rs-fMRI indices were calculated. The results showed that SCD individuals had a lower amplitude of low-frequency fluctuations dynamics in bilateral hippocampus (HP)/parahippocampal gyrus (PHG)/fusiform gyrus (FG) and bilateral cerebellum, a lower fractional amplitude of low-frequency fluctuation dynamics in bilateral precuneus (PreCu) and paracentral lobule, and a lower regional homogeneity dynamics in bilateral cerebellum, vermis, and left FG compared with the other two groups, whereas those in MCI patients were higher (Gaussian random field–corrected, voxel-level P < 0.001, cluster-level P < 0.05). Furthermore, SCD individuals had higher concordance in bilateral HP/PHG/FG, temporal lobe, and left midcingulate cortex than NCs, but those in MCI were lower than those in NCs. No correlation between concordance values and neuropsychological scale scores was found. SCD individuals showed both dynamics and concordance-related alterations in IBA, which indicates a compensatory mechanism in SCD individuals. Temporal dynamics analysis offers a novel approach to capturing brain alterations in individuals with SCD.
Highlights
The neurodegenerative changes that eventually develop into dementia due to Alzheimer disease (AD) begin to accumulate approximately 20 years before clinical symptoms appear (Sperling et al, 2011)
least significant difference (LSD) post-hoc analysis revealed that only the Auditory Verbal Learning Test (AVLT) immediate memory scores (P = 0.033) were significantly lower in the Subjective cognitive decline (SCD) group than those in NCs; all of the other significant neuropsychological differences resulted from comparisons between the mild cognitive impairment (MCI) group and the other two groups, respectively (P < 0.001) (Supplementary Table 1)
Post-hoc analysis using LSD testing showed that dALFF, dfALFF, and dReHo in the MCI group were higher than those in the NC group, whereas these measures were lower in the SCD group than those in the other two groups (Figures 2–4, Table 2)
Summary
The neurodegenerative changes that eventually develop into dementia due to Alzheimer disease (AD) begin to accumulate approximately 20 years before clinical symptoms appear (Sperling et al, 2011). Li et al assessed the intrinsic connectivity network of SCD individuals and found that SCD individuals show higher degree centrality (DC) in bilateral hippocampus (HP) and left fusiform gyrus (FG), but lower DC in the inferior parietal region than controls (Li et al, 2018). All these studies indicate a possible compensatory mechanism affecting the intrinsic brain activity (IBA) of SCD individuals. Research has revealed no significant differences in cortical thickness in SCD individuals compared with healthy people (Sun et al, 2016), suggesting that the change in IBA might be a more sensitive biomarker for SCD than structure alterations
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