Decreased activity with increased background network efficiency in amnestic MCI during a visuospatial working memory task

Abstract

Recent studies have demonstrated the working memory impairment in patients with amnestic mild cognitive impairment (aMCI). However, the neurophysiological basis of the working memory deficit in aMCI is poorly understood. The aim of this study was to explore the abnormal activity during encoding and recognition procedures, as well as the reorganization of the background network maintaining the working memory state in aMCI. Using event-related fMRI during a visuospatial working memory task with three recognition difficulty levels, the task-related activations and network efficiency of the background network in 17 aMCI patients and 19 matched controls were investigated. Compared with cognitively healthy controls, patients with aMCI showed significantly decreased activity in the frontal and visual cortices during the encoding phase, while during the recognition phase, decreased activity was detected in the frontal, parietal, and visual regions. In addition, increased local efficiency was also observed in the background network of patients with aMCI. The results suggest patients with aMCI showed impaired encoding and recognition functions during the visuospatial working memory task, and may pay more effort to maintain the cognitive state. This study extends our understanding of the impaired working memory function in aMCI and provides a new perspective to investigate the compensatory mechanism in aMCI.

Frequency-Dependent Brain Regional Homogeneity Alterations in Patients with Mild Cognitive Impairment during Working Memory State Relative to Resting State

“…As a key structure in working memory processing, the PFC exerts control over behavior by biasing the salience of mnemonic representations and adjudicating among competing context-dependent rules (D’Esposito and Postle, 2015 ). Previous studies found that MCI patients show significantly decreased activity in the PFC and significantly increased activity in the parietal-occipital regions during working memory tasks (Bokde et al, 2010 ; Lou et al, 2015 ). Consistent with these findings, the PFC and parietal occipital-regions showed group × state interactions in our study.…”

“…In addition, the working memory component of our task was not very pure because processing consisted of encoding, retrieval, and sub-resting sessions (for details, see “Materials and Methods” Section). Given the observation of decreased activity in different regions during the encoding and retrieval processes of a spatial working memory task in MCI patients (Lou et al, 2015 ), future studies should separate these two subprocesses to explore whether brain oscillations vary according to these subtypes in working memory states.…”

“…Rapid declines in working memory as well as delayed recall and spatial memory have been reported following the conversion of MCI to Alzheimer’s disease (AD; Cloutier et al, 2015 ). Studies investigating the corresponding neural mechanisms of MCI have examined altered brain activation during working memory tasks (Bokde et al, 2010 ; Lou et al, 2015 ; Migo et al, 2015 ); however, the pattern of intrinsic brain oscillations during a working memory task has not yet been explored for comparison. Studies have also evaluated functional network differences between resting and task states.…”

“…Furthermore, alterations between resting and task states have been associated with task performance in children with autism spectrum disorders (You et al, 2013 ). Of note, Lou et al ( 2015 ) evaluated background network efficiency (an index based on graph theory) during a working memory task and reported increased background network efficiency in MCI patients that was hypothesized to compensate for decreased working memory capacity (Lou et al, 2015 ). However, no study to date has evaluated the impairment of specific brain network regions or the properties of associated brain networks (e.g., functional connectivity [FC], regional homogeneity [ReHo], and amplitude of low-frequency fluctuations [ALFF]) in MCI patients in resting vs. working memory states.…”

Changes in resting-state Functional Connectivity of Cerebellum in amnestic Mild Cognitive Impairment and Alzheimer’s disease: a case-control study

“…These ndings raise the opportunity that the cerebellum is not a "silent bystander" in AD, and the cerebellum may not be an optimal choice for the reference region. With the development of neuroimaging, growing studies reported the cerebellar atrophy and functional alteration in AD [8][9][10][11][12][13]. However, till now, the studies about the changes of cerebellum in AD patients are still limited, and results are not consistent.…”