Abstract
Research indicates that a subtle cognitive decline, accompanied by pathological changes, occurs in individuals with subjective memory complaints (SMC). However, there is less evidence regarding the measurement of resting-state functional connectivity to detect subtle brain network alterations in neurodegenerative illnesses before cognitive change manifestation. We investigated the correlation between SMC and cognitive performance and explored functional and structural brain changes underlying SMC severity, using behavioral and brain imaging data-driven approaches. We observed that SMC was associated with depression but not with cognitive test scores, implying that SMC represent the “worried-well”; however, this model explains only 15% of the target variance. Using a conservative threshold, we observed connectivity related to SMC severity in the lingual gyrus, cuneus, anterior insula, and superior parietal lobule. Post-hoc analysis indicated that occipital and parietal functional connectivity increased with SMC severity. In contrast, volumetric alterations were not associated with SMC, even after applying a liberal threshold. Our findings suggest that altered resting-state functional connectivity in regions associated with SMC might reflect early compensatory changes that occur before cognitive and structural abnormalities develop.
Highlights
There has been growing interest in individuals with subjective memory complaints (SMC; known as subjective cognitive impairment, subjective memory impairment, subjective cognitive decline, and other terminology) (Abdulrab and Heun, 2008) who experience changes in their memory function
SMC may represent a prodromal state of mild cognitive impairment (MCI) (Dubois et al, 2016; Jessen et al, 2014; Petersen et al, 2001), some studies have demonstrated that the cognitive state is not always related to actual detectable memory function (Harwood et al, 2004; Jungwirth et al, 2004; Kryscio et al, 2014)
We aimed to explore the relationship between SMC and resting-state functional connectivity (rs-FC) by using rs-functional MRI (fMRI)
Summary
There has been growing interest in individuals with subjective memory complaints (SMC; known as subjective cognitive impairment, subjective memory impairment, subjective cognitive decline, and other terminology) (Abdulrab and Heun, 2008) who experience changes in their memory function. Previous studies have attempted to identify key brain regions associated with SMC using biochemical, structural, and functional methods. The resulting resting-state functional connectivity (rs-FC) correlates with the activity of distant brain regions Measuring this allows the detection of subtle brain network alterations in neurodegenerative illnesses, such as AD, before the manifestation of cognitive and behavioral changes (Sheline and Raichle, 2013). Based on previous reports (Hafkemeijer et al, 2013; Jessen et al, 2006; Schultz et al, 2015; Cooley et al, 2015), we hypothesized that the rs-FC and volume of medial and posterior regions, such as the hippocampus, entorhinal, thalamus, posterior cingulate, fusiform, cuneus, and precuneus, which form part of the default-mode and visual networks, would be modulated by SMC severity. As a complementary analysis, we include follow-up data indicating that SMC are related to later cognitive decline
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