Mild Cognitive Impairment Is Not "Mild" at All in Altered Activation of Episodic Memory Brain Networks: Evidence from ALE Meta-Analysis.

Pengyun Wang,Rui Li,Juan Li,Hui-Jie Li,Lijuan Huo

doi:10.3389/fnagi.2016.00260

Abstract

The present study conducted a quantitative meta-analysis aiming at assessing consensus across the functional neuroimaging studies of episodic memory in individuals with amnestic mild cognitive impairment (aMCI) and elucidating consistent activation patterns. An activation likelihood estimation (ALE) was conducted on the functional neuroimaging studies of episodic encoding and retrieval in aMCI individuals published up to March 31, 2015. Analyses covered 24 studies, which yielded 770 distinct foci. Compared to healthy controls, aMCI individuals showed statistically significant consistent activation differences in a widespread episodic memory network, not only in the bilateral medial temporal lobe and prefrontal cortex, but also in the angular gyrus, precunes, posterior cingulate cortex, and even certain more basic structures. The present ALE meta-analysis revealed that the abnormal patterns of widespread episodic memory network indicated that individuals with aMCI may not be completely “mild” in nature.

Highlights

Mild cognitive impairment (MCI) is a state where individuals display certain form of cognitive dysfunction, but still maintain the intact ability to perform basic daily activities
Only those that met the following criteria were examined and taken into consideration: (1) performing the diagnosis of amnestic MCI (aMCI) according to Petersen et al (2001); Petersen (2004); or Winblad et al (2004) was; (2) reporting positron emission tomography (PET) or functional magnetic resonance imaging (fMRI) results of episodic encoding and/or retrieval paradigms compared to baseline task(s); (3) describing results of independent groups (MCIs and matched controls) or between-group comparisons based on a whole-brain analysis; and (4) using standard stereotactic coordinates to list peaks of significant activation (Talairach and Tournoux, 1988) or Montreal Neurologic Institute (MNI) space
Peak MNI coordinates, Brodmann areas (BA), and cluster sizes of significant activation likelihood estimation (ALE) regions are summarized in Table 2 and Supplementary Table 1

Summary

Introduction

Mild cognitive impairment (MCI) is a state where individuals display certain form of cognitive dysfunction, but still maintain the intact ability to perform basic daily activities. MCI is generally considered as a transitional stage between normal aging and clinical dementia (Petersen, 2004). A meta-analysis reported that the annual conversion rate from MCI to dementia is approximately 5–10% (Mitchell and Shiri Feshki, 2009), which is obviously higher than the incidence rates from normal elderly to dementia (1–2% per year) (Petersen, 2004). According to Petersen (2004), the MCI individuals with memory impairment are described as amnestic MCI (aMCI) and without memory impairment as non-amnestic MCI (naMCI). 80% of individuals with aMCI progress to Alzheimer’s disease (AD) which is the most common form of dementia after a clinical follow-up of 6 years (Petersen, 2004).

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