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

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.

Disturbed temporal dynamics of episodic retrieval activity with preserved spatial activity pattern in amnestic mild cognitive impairment: A simultaneous EEG-fMRI study

“…For example, the IPL is assumed to support the recall of item details; the Pcu/PCC is linked to decision-related retrieval processes, and the prefrontal cortex is thought to be involved in the top-down control of memory retrieval, such as post-retrieval monitoring and evaluation ( Spaniol et al, 2009 ). The decreased activation in the left lateral prefrontal area in the aMCI group indicate impaired cognitive control on episodic memory retrieval in aMCI individuals, which has been demonstrated previously ( Wang et al, 2016 ). This result corresponds to the observation that aMCI subjects also showed inferior executive function in neuropychological tests.…”

Model-based assessment and neural correlates of spatial memory deficits in mild cognitive impairment

“…In contrast, as the striatum and pre-SMA have both been linked to individuals' ability to modulate their level of caution in choice RT tasks (Forstmann et al, 2008;, lower activity of these regions in MCI is consistent with their higher level of caution. When viewed within the context of the wider literature on cognitive (McLaughlin et al, 2014;Zheng et al, 2012;Levinoff et al, 2005) and neuroimaging (Hampstead et al, 2011;Zhang et al, 2015;Wang, et al, 2016) deficits in MCI, the current findings support the notion that aberrations in cognitive performance in MCI are related to widespread dysfunction that extends beyond the medial temporal lobes.…”

“…However, accumulating evidence suggests that this focus may be based on an overly simplistic view of cognitive dysfunction. For example, recent neuroimaging work has found evidence for widespread neocortical abnormalities in MCI that extend beyond the medial temporal lobe; individuals with MCI appear to display hypo-activation of a broad range of frontal, parietal and subcortical areas during episodic memory encoding and retrieval tasks (Hampstead et al, 2011;Wang, et al, 2016;but see: Miller et al, 2008;Dickerson et al, 2005). We recently reported marked shifts in MCI patients' pattern of task-related effective connectivity during encoding and retrieval that were primarily focused outside of medial temporal lobe structures (Hampstead et al, 2016).…”

Disturbed temporal dynamics of episodic retrieval activity with preserved spatial activity pattern in amnestic mild cognitive impairment: A simultaneous EEG-fMRI study

“…For example, the IPL is assumed to support the recall of item details; the Pcu/PCC is linked to decision-related retrieval processes, and the prefrontal cortex is thought to be involved in the top-down control of memory retrieval, such as post-retrieval monitoring and evaluation (8). Decreased activation in the left lateral prefrontal area indicated de cits in top-down memory retrieval control in aMCI individuals, which has been demonstrated previously (16). Notably, the episodic retrieval pattern identi ed in this study was mainly located in the left-lateralized brain regions, and was likely attributed to verbal processing.…”