Dissociating atrophy and hypometabolism impact on episodic memory in mild cognitive impairment
ABSTRACT 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.
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- "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). "
ABSTRACT: Cancer involves stressful events. One aspect of cognition that is impacted by stress is episodic autobiographical memory (EAM). EAM is intimately linked to self-representation. Some studies have revealed impairment of EAM in patients with breast cancer in remission. Yet, these studies failed to differentiate between the influence of adjuvant treatments and that of psychosocial factors. We therefore assessed the psychological impact of breast cancer diagnosis on EAM and self-representation profiles prior to any adjuvant treatment. Patients newly diagnosed with breast cancer (n=31) and women without any history of cancer (n=49) were compared on state anxiety, EAM and its emotional characteristics, and self-representations. The most anxious patients retrieved fewer emotional details for memories than the controls, and had lower self-representation scores than the least anxious patients, who had no deficits in emotional detail retrieval. Our results revealed distinct EAM profiles for patients, reflecting two contrasting modes of coping with breast cancer. Copyright © 2015 Elsevier Inc. All rights reserved.Consciousness and Cognition 05/2015; 35. DOI:10.1016/j.concog.2015.04.016 · 2.31 Impact Factor
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- "Consistent with this hypothesis, neuroimaging studies of episodic anterograde memory in MCI have shown the involvement of specific structures of the core network. For instance, an association has been found between the metabolism of the posterior cingulate cortex and episodic memory performance in MCI (Bastin et al., 2010; Chételat et al., 2003). Furthermore, controlled retrieval of episodic information in MCI patients has been related to metabolic activity in the dorsomedial prefrontal cortex (Bastin et al., 2010). "
ABSTRACT: Autobiographical memory in amnestic Mild Cognitive Impairment (aMCI) is characterized by impaired retrieval of episodic memories, but relatively preserved personal semantic knowledge. This study aimed to identify (via FDG-PET) the neural substrates of impaired episodic specificity of autobiographical memories in 35 aMCI patients compared with 24 healthy elderly controls. Significant correlations between regional cerebral activity and the proportion of episodic details in autobiographical memories from two life periods were found in specific regions of an autobiographical brain network. In aMCI patients, more than in controls, specifically episodic memories from early adulthood were associated with metabolic activity in the cuneus and in parietal regions. We hypothesized that variable retrieval of episodic autobiographical memories in our aMCI patients would be related to their variable capacity to reactivate specific sensory-perceptual and contextual details of early adulthood events linked to reduced (occipito-parietal) visual imagery and less efficient (parietal) attentional processes. For recent memories (last year), a correlation emerged between the proportion of episodic details and activity in lateral temporal regions and the temporo-parietal junction. Accordingly, variable episodic memory for recent events may be related to the efficiency of controlled search through general events likely to provide cues for the retrieval of episodic details and to the ability to establish a self perspective favouring recollection. Hum Brain Mapp, 2012. © 2012 Wiley Periodicals, Inc.Human Brain Mapping 08/2013; 34(8). DOI:10.1002/hbm.22032 · 6.92 Impact Factor
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- "As pointed out by cognitivo-metabolic correlation studies (Desgranges et al., 1998; for review, see Salmon et al., 2008), the functional disturbance of this limbic structure is highly linked to the patients' episodic memory deficit. This approach has also highlighted other regions responsible for episodic memory deficits in the earlier stages of the disease, such as the posterior cingulate cortex (Chételat et al., 2003). Task-related functional brain imaging techniques have been used to further investigate the substrate of episodic impairment in AD. "
ABSTRACT: The aim of the present study was to explore the cerebral substrates of episodic memory disorders in Alzheimer’s disease (AD) and investigate patients’ hyperactivations frequently reported in the functional imaging literature. It remains unclear whether some of these hyperactivations reflect real increased activity or deactivation disturbances in the default mode network (DMN). Using positron emission tomography (15O-H2O), cerebral blood flow was measured in 11 AD patients and 12 healthy elderly controls at rest and during encoding and stem-cued recall of verbal items. Subtractions analyses between the target and control conditions were performed and compared between groups. The average signal was extracted in regions showing hyperactivation in AD patients versus controls in both contrasts. To determine whether hyperactivations occurred in regions that were activated or deactivated during the memory tasks, we compared signal intensities between the target conditions versus rest. Our results showed reduced activation in AD patients compared to controls in several core episodic memory regions, including the medial temporal structures, during both encoding and retrieval. Patients also showed hyperactivations compared to controls in a set of brain areas. Further analyses conducted on the signal extracted in these areas indicated that most of these hyperactivations actually reflected a failure of deactivation. Indeed, whereas almost all of these regions were significantly more activated at rest than during the target conditions in controls, only one region presented a similar pattern of deactivation in patients. Altogether, our findings suggest that hyperactivations in AD must be interpreted with caution and may not systematically reflect increased activity. Although there has been evidence supporting the existence of genuine compensatory mechanisms, dysfunction within the DMN may be responsible for part of the apparent hyperactivations reported in the literature on AD.Frontiers in Human Neuroscience 05/2012; 6(4):107. DOI:10.3389/fnhum.2012.00107 · 2.90 Impact Factor