Deficits in episodic memory retrieval reveal impaired default mode network connectivity in amnestic mild cognitive impairment

Abstract

Amnestic mild cognitive impairment (aMCI) is believed to represent a transitional stage between normal healthy ageing and the development of dementia. In particular, aMCI patients have been shown to have higher annual transition rates to Alzheimer's Disease (AD) than individuals without cognitive impairment. Despite intensifying interest investigating the neuroanatomical basis of this transition, there remain a number of questions regarding the pathophysiological process underlying aMCI itself. A number of recent studies in aMCI have shown specific impairments in connectivity within the default mode network (DMN), which is a group of regions strongly related to episodic memory capacities. However to date, no study has investigated the integrity of the DMN between patients with aMCI and those with a non-amnestic pattern of MCI (naMCI), who have cognitive impairment, but intact memory storage systems. In this study, we contrasted the DMN connectivity in 24 aMCI and 33 naMCI patients using seed-based resting state fMRI. The two groups showed no statistical difference in their DMN intra-connectivity. However when connectivity was analysed according to performance on measures of episodic memory retrieval, the two groups were separable, with aMCI patients demonstrating impaired functional connectivity between the hippocampal formation and the posterior cingulate cortex. We provide evidence that this lack of connectivity is driven by impaired communication from the posterior cingulate hub and does not simply represent hippocampal atrophy, suggesting that posterior cingulate degeneration is the driving force behind impaired DMN connectivity in aMCI.

Vascular risk factors, cerebrovascular reactivity, and the default-mode brain network

“…While several studies have examined the association of VRF and vascular pathology on brain function in different brain regions (Claus et al, 1998; Jennings et al, 2005; Glodzik et al, 2011; Beason-Held et al, 2012), this is the first to examine the effects of VRF on CVR with respect to the DMN in a large sample of relatively young subjects. Disruption of the DMN, which represents a network of major interest in aging and AD, and has been shown in different patient groups, including those with mild cognitive impairment (MCI) and normal older controls (Sperling, 2007;Dunn et al, 2014), may in part be related to reduced cerebrovascular function.…”

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

“…Due to the limitations of the ALE technique, the present study is unfortunately only able to describe the differences of brain activation between aMCI individuals and healthy controls. Recent studies have proved that the functional connectivity within this mnemonic network is declined in individuals with aMCI during resting state, which is associated with their memory impairment (Li et al, 2013; Dunn et al, 2014). The future research probably requires the investigation of the functional connectivity characters within this mnemonic network in individuals with aMCI during episodic encoding and retrieval processing.…”

Resting-state synchrony between the retrosplenial cortex and anterior medial cortical structures relates to memory complaints in subjective cognitive impairment

“…Functional connectivity measures are thought to reflect the sum of both direct and indirect synaptic connections between neural hubs (Dunn et al, 2014;Greicius et al, 2009;Sperling et al, 2010). The SLF is composed of long bundles of neurons connecting the front and the back of the cerebrum.…”