The present study aims to unravel, in the same study, both morphological and functional specific substrates of encoding versus retrieval deficits in patients with amnestic mild cognitive impairment (MCI). For this purpose, 21 highly screened MCI patients with isolated memory impairment, who attended a memory clinic and fulfilled operational criteria for MCI, underwent (i) two episodic memory subtests designed to assess preferentially either incidental encoding or retrieval capacity; (ii) a high-resolution T1-weighted volume MRI scan; and (iii) a resting state [18F]fluoro-2-deoxy-D-glucose PET study. Using statistical parametric mapping, positive correlations between memory scores on one hand, and grey matter density and normalized partial volume effect-corrected brain glucose utilization (ncCMRglc) on the other hand, were computed. Deficits in both encoding and retrieval were correlated with declines in hippocampal region grey matter density. The encoding subtest also correlated with hippocampal ncCMRglc, whereas the retrieval subtest correlated with the posterior cingulate area ncCMRglc only. The present findings highlight a distinction in the neural substrates of encoding and retrieval deficits in MCI. Furthermore, they unravel a partial dissociation between metabolic and structural correlates, suggesting distinct interpretations. Hippocampal atrophy was related to both encoding and retrieval deficits, possibly reflecting a direct effect on hippocampal functioning, as well as an indirect effect, through remote functional disruption, on posterior cingulate region synaptic function, respectively.
"Neuropsychological tests were administered to all participants to assess their cognitive abilities: two tests of verbal and visual episodic memory processes that had previously been developed in our laboratory, based on the Encoding, Storage, Retrieval (ESR) paradigm (Chetelat et al., 2003; Eustache, Desgranges, & Lalevée, 1998; Fouquet et al., 2012), the Digit Span Backward, Letter-Number Sequencing and Arithmetic subtests of the Wechsler Adult Intelligence Scale (WAIS; Wechsler, 2008), the Trail Making Test (TMT) Parts A and B (Reitan, 1992), formal and semantic verbal fluency (Cardebat, Doyon, Puel, Goulet, & Joanette, 1990), and the d2 Test of Attention (Brickenkamp & Zillmer, 1998). "
Consciousness and Cognition 05/2015; 35. DOI:10.1016/j.concog.2015.04.016 · 2.31 Impact Factor
"Neuroimaging studies showed that, in both diseases, the medial temporal lobe undergoes atrophy (Chan et al., 2001; Galton et al., 2001; Nestor et al., 2006; Schroeter and Neumann, 2011; Duval et al., 2012; La Joie et al., 2012) and hypometabolism (Desgranges et al., 2007; Rabinovici et al., 2008; Mosconi et al., 2005; Nestor et al., 2006; Duval et al., 2012; La Joie et al., 2012). This has been highlighted as a paradox given the widely documented relationship between hippocampal impairment and early episodic memory deficits in AD (Deweer et al., 1995; Kö hler et al., 1998; Laakso et al., 2000; Scheltens et al., 1992; Ché telat et al., 2003) faced to the relative preservation of dayto-day episodic memory in SD (Chan et al., 2001; Galton et al., 2001; Nestor et al., 2006; Pleizier et al., 2012). Previous authors have therefore proposed that, beyond the hippocampus, episodic memory impairment in AD would be due to the dysfunction of additional episodic memory-related regions that would be spared in SD (Hornberger and Piguet, 2012; Nestor et al., 2006). "
"The PCC is the most common site of early metabolic and perfusion abnormalities occurring upon aging and AD (Buckner, Andrews-Hanna & Schacter, 2008; Chetelat et al., 2003). Disrupted connectivity between the Hp/EC and the PCC has been proposed as a functional mechanism of PCC hypometabolism and hypoperfusion, phenomena that are observed in the early stage of AD (Mevel et al., 2011). "
[Show abstract][Hide abstract] ABSTRACT: Objectives. Aging is the major risk factor for Alzheimer Disease (AD) and Mild Cognitive Impairment (MCI). The aim of this study was to identify novel modifications of brain functional connectivity in MCI patients. MCI individuals were compared to healthy elderly subjects.
Methods. We enrolled 37 subjects (age range 60–80 y.o.). Of these, 13 subjects were affected by MCI and 24 were age-matched healthy elderly control (HC). Subjects were evaluated with Mini Mental State Examination (MMSE), Frontal Assessment Battery (FAB), and prose memory (Babcock story) tests. In addition, with functional Magnetic Resonance Imaging (fMRI), we investigated resting state network (RSN) activities. Resting state (Rs) fMRI data were analyzed by means of Independent Component Analysis (ICA). Subjects were followed-up with neuropsychological evaluations for three years.
Results. Rs-fMRI of MCI subjects showed increased intrinsic connectivity in the Default Mode Network (DMN) and in the Somatomotor Network (SMN). Analysis of the DMN showed statistically significant increased activation in the posterior cingulate cortex (PCC) and left inferior parietal lobule (lIPL). During the three years follow-up, 4 MCI subjects converted to AD. The subset of MCI AD-converted patients showed increased connectivity in the right Inferior Parietal Lobule (rIPL). As for SMN activity, MCI and MCI-AD converted groups showed increased level of connectivity in correspondence of the right Supramarginal Gyrus (rSG).
Conclusions. Our findings indicate alterations of DMN and SMN activity in MCI subjects, thereby providing potential imaging-based markers that can be helpful for the early diagnosis and monitoring of these patients.
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