Abstract
Previous studies investigating working memory performance in patients with mild cognitive impairment (MCI) have mainly focused on the neural mechanisms of alterations in activation. To date, very few studies have investigated background network alterations in the working memory state. Therefore, the present study investigated the static and temporal dynamic changes in the background network in MCI patients during a working memory task. A hybrid delayed-match-to-sample task was used to examine working memory performance in MCI patients. Functional magnetic resonance imaging (fMRI) data were collected and the marker of amplitude of low-frequency fluctuations (ALFF) was used to investigate alterations in the background network. The present study demonstrated static and dynamic alterations of ALFF in MCI patients during working memory tasks, relative to the resting state. Traditional static analysis revealed that ALFF decreased in the right ventrolateral prefrontal cortex (VLPFC), right dorsolateral PFC (DLPFC), and left supplementary motor area for normal controls (NCs) in the working memory state. However, the same regions showed increased ALFF in MCI patients. Furthermore, relative to NCs, MCI patients demonstrated altered performance-related functional connectivity (FC) patterns, with the right VLPFC and right DLPFC as ROIs. In terms of temporal dynamic analysis, the present study found that in the working memory state dynamic ALFF of bilateral thalamus regions was increased in NCs but decreased in MCI patients. Additionally, MCI patients demonstrated altered performance-related coefficient of variation patterns; the regions in MCI patients were larger and more widely distributed in the parietal and temporal lobes, relative to NCs. This is the first study to examine static and temporal dynamic alterations of ALFF in the background network of MCI patients in working memory states. The results extend previous studies by providing a new perspective on the neural mechanisms of working memory deficits in MCI patients.
Highlights
Mild cognitive impairment (MCI) is a syndrome where individuals display certain forms of cognitive dysfunction, but the ability to perform basic daily activities remains intact (Petersen, 2004)
For all of the three clusters, post hoc t-tests showed that the value of Amplitude of low-frequency fluctuations (ALFF) was higher in MCI patients than in NCs during the resting state, while there was no difference between two groups during the working memory state
Since these interaction effects were mainly due to abnormal hyperactivity in MCI patients during the resting state, the Pearson correlations between the brain ALFF activity and working memory performance in MCI patients was calculated to examine whether the hyperactivity was a compensatory process due to the reduced functionality of these brain regions
Summary
Mild cognitive impairment (MCI) is a syndrome where individuals display certain forms of cognitive dysfunction, but the ability to perform basic daily activities remains intact (Petersen, 2004). Many studies have focused on the deficit in working memory displayed by MCI patients (Klekociuk and Summers, 2014; Kirova et al, 2015) and the corresponding neural mechanisms, including altered activation during working memory tasks (Bokde et al, 2010; Lou et al, 2015; Migo et al, 2015). Previous studies found altered local synchronization (indexed by regional homogeneity, ReHo; Wang et al, 2016) and distant synchronization (indexed by degree of centrality, DC; Wang et al, 2017) of the background network in MCI patients during a working memory task. Whether the oscillation of an individual voxel in the background network is altered in MCI patients during a working memory task is still unknown
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