Activation of brain regions vulnerable to Alzheimer's disease: The effect of mild cognitive impairment

Abstract

This study examined the functionality of the medial temporal lobe (MTL) and posterior cingulate (PC) in mild cognitive impairment amnestic type (MCI), a syndrome that puts patients at greater risk for developing Alzheimer disease (AD). Functional MRI (fMRI) was used to identify regions normally active during encoding of novel items and recognition of previously learned items in a reference group of 77 healthy young and middle-aged adults. The pattern of activation in this group guided further comparisons between 14 MCI subjects and 14 age-matched controls. The MCI patients exhibited less activity in the PC during recognition of previously learned items, and in the right hippocampus during encoding of novel items, despite comparable task performance to the controls. Reduced fMRI signal change in the MTL supports prior studies implicating the hippocampus for encoding new information. Reduced signal change in the PC converges with recent research on its role in recognition in normal adults as well as metabolic decline in people with genetic or cognitive risk for AD. Our results suggest that a change in function in the PC may account, in part, for memory recollection failure in AD.

Alterations in Memory Networks in Mild Cognitive Impairment and Alzheimer's Disease: An Independent Component Analysis

“…The more impaired MCI subjects (based on CDR-SB score), showed a pattern of decreased activation in the MTL and functionally connected regions that strongly resembled the pattern seen in mild AD subjects. These results are similar to reports from other groups who have studied more impaired MCI subjects (Machulda et al, 2003;Johnson et al, 2006), and suggests that the variability in published fMRI studies of MCI is likely related to the heterogeneity of subjects within the MCI continuum. Furthermore, our findings are consistent with the theory that the late stage of MCI is likely already very mild AD (Morris and Cummings, 2005).…”

Can multi-modal neuroimaging evidence from hippocampus provide biomarkers for the progression of amnestic mild cognitive impairment?

“…Furthermore, hippocampal hypoactivation is correlated with the clinical severity of memory loss in aMCI patients [62] . Using an item-based old/new recognition retrieval task, Johnson and colleagues have demonstrated right hippocampal hypoactivation in aMCI patients compared to controls [7] . In contrast, several studies have shown greater hippocampal activation in aMCI patients relative to controls.…”

“…Structural and functional changes in the hippocampus are ression and trajectory and the related pathology [7] . Previous studies have indicated that hippocampal atrophy is the most prominent structural hallmark of progression from aMCI to AD [8,9] .…”

Functional MRI in the early diagnosis of Alzheimer’s disease: is it time to refocus?

“…Nevertheless, a common finding in studies of healthy subjects compared with AD or MCI patients is decreased MTL activation in the patients [25,[32][33][34][35][36][37][38][39]. The interpretation is typically that reduced activation in this region corresponds to the memory deficits exhibited by these patients.…”