Impaired explicit self-awareness but preserved behavioral regulation in patients with Alzheimer Disease

Objectives: Impairments of metacognitive skills represent a critical symptom in Alzheimer Disease (AD) because it frequently results in a lack of self-awareness. However, recent findings suggest that, despite an inability to explicitly estimate their own cognitive functioning, patients might demonstrate some implicit recognition of difficulties. In this study, we tested whether a behavioral dissociation between explicit and implicit measures of metacognition can be found in both healthy older controls (n = 20) and AD patients (n = 20). Methods: Our two groups of participants (AD vs. Controls) were asked to complete a forced-choice perceptual identification test and to explicitly rate their confidence in each decision (i.e., explicit measure of metacognition). Moreover, they also had the opportunity to ask for a cue to help them decide if their response was correct (i.e., implicit measure of metacognition). Results: Data revealed that all participants asked for a cue more often after an incorrect response than after a correct response in the forced-choice identification test, indicating a good ability to implicitly introspect on the results of their cognitive operations. On the contrary, only healthy participants displayed metacognitive sensitivity when making explicit confidence judgments. Conclusion: Our findings suggest that implicit metacognition may be less affected than explicit metacognition in Alzheimer’s disease

Temporal signature of a ‘beyond-viewpoint’ exemplar-level processing in visual object recognition

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Single and multicomponent sorption of CO2, CH4 and N-2 in a microporous metal-organic framework

Single and multicomponent fixed-bed adsorption of CO2, N-2, and CH4 on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO2 and the loadings of CH4 and N-2 are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO2 is one order of magnitude faster than for CH4 and N-2.This work was supported by an Award CHE 0718281 from the National Science Foundation (B.C.), the University of Texas-Pan American (UTPA) through a Faculty Research Council Award (B.C), in part by the Welch Foundation (Grant BG-0017) to the Department of Chemistry at UTPA. J.A.C.S. acknowledges financial support provided by national research grant FCT=POCTI=EQU=60828=2004 and by LSRE financing by FEDER=POCI=2010. P.S.B. acknowledges his Ph.D. scholarship by FCT (SFRH=BD=30994=2006), and L.B. acknowledges Henri Pieper Grant (Institute HEMES Gramme, Belgium) for the financial support

A microporous metal-organic framework for separation of CO2/N-2 and CO2/CH4 by fixed-bed adsorption

A microporous MOF Zn(BDC)(4,4'-Bipy)0.5 (MOF-508b, BDC = 1,4-benzenedicarboxylate, 4,4'-Bipy = 4,4'-bipyridine) was examined for the separation and removal of CO2 from its binary CO2/N-2 and CO2/CH4 and ternary CO2/CH4/N-2 mixtures by fixed-bed adsorption. With one-dimensional pores of about 4.0 x 4.0 angstrom to induce their differential interactions with the three components, MOF-508b exhibits highly selective adsorption to CO2 with the,adsorption capacity of 26.0 wt % at 303 K and 4.5 bar. This is the first example of microporous MOFs for the separation and removal of CO2 from its binary and ternary mixtures by fixed-bed adsorption, establishing the feasibility of the emerging microporous MOFs for their potential. applications in this very important industrial and environmental process

Testing a New Memory Task Sensitive to Early Entorhinal/Perirhinal Atrophy in Alzheimer's disease

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Fluency-Based Memory Decisions in Alzheimer’s Disease: A Matter of Source Detection?

Objective: The primary aim of this study was to test whether differences in the ability of patients with Alzheimer Disease (AD) and healthy participants to detect alternative sources of fluency can account for differences observed in the use of fluency - i.e., the ease with which information is processed - as a cue for memory. Method: Twenty-two patients with AD and 22 matched controls were presented with three forced-choice visual recognition tests. In each test, an external source of fluency was provided by manipulating the perceptual quality of the items during the test phase. The detectability of the perceptual manipulation varied in each test (i.e., 10%, 20%, or 30% contrast reduction were given). Results: Data indicated that AD patients rely on fluency in a similar extent than older adults as long as they demonstrate intact detection of differences in the perceptual quality of the items. Specifically, it appears that patients’ ability to visually discriminate stimuli differing in terms of their perceptual quality is critical for patients to be able to implement strategies to appropriately use or correctly disqualify fluency during a recognition task. Conclusion: Overall, these findings suggest that the disruption of some basic cognitive processes could prevent AD patients to experience fluency in a similar extent than healthy controls. However, when the ability to detect differences in the perceptual quality of the stimuli was taken into account, patients appeared to be as able as controls to rely on fluency to guide their memory decisions

The Neural Substrates of Memory Suppression: A fMRI Exploration of Directed Forgetting

The directed forgetting paradigm is frequently used to determine the ability to voluntarily suppress information. However, little is known about brain areas associated with information to forget. The present study used functional magnetic resonance imaging to determine brain activity during the encoding and retrieval phases of an item-method directed forgetting recognition task with neutral verbal material in order to apprehend all processing stages that information to forget and to remember undergoes. We hypothesized that regions supporting few selective processes, namely recollection and familiarity memory processes, working memory, inhibitory and selection processes should be differentially activated during the processing of to-be-remembered and to-be-forgotten items. Successful encoding and retrieval of items to remember engaged the entorhinal cortex, the hippocampus, the anterior medial prefrontal cortex, the left inferior parietal cortex, the posterior cingulate cortex and the precuneus; this set of regions is well known to support deep and associative encoding and retrieval processes in episodic memory. For items to forget, encoding was associated with higher activation in the right middle frontal and posterior parietal cortex, regions known to intervene in attentional control. Items to forget but nevertheless correctly recognized at retrieval yielded activation in the dorsomedial thalamus, associated with familiarity-based memory processes and in the posterior intraparietal sulcus and the anterior cingulate cortex, involved in attentional processes

Neural correlates of impaired cognitive processes underlying self-unawareness in Alzheimer’s disease

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Distinct profiles of impaired associative memory and underlying cerebral networks in Alzheimer's disease

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