Étude comparative de la mémoire de source et des faux souvenirs dans la maladie d’Alzheimer et la maladie de Parkinson avec et sans démence

Dans les dernières années, les études sur les maladies neurodégénératives telles que la maladie d’Alzheimer (MA) et la maladie de Parkinson sans démence (MP) et avec démence (MPD) ont été nombreuses, mais la différenciation de ces patients sur la base de leur profil cognitif doit être encore améliorée. Effectivement, l’évaluation clinique peut s’avérer difficile en raison du peu de spécificité dans la présentation de leurs déficits neuropsychologiques. Ceci s’explique par la variabilité et le chevauchement des processus cliniques et pathologiques affectant essentiellement les mêmes régions/fonctions, soit celles liées aux lobes temporaux médians (LTM)/Mémoire (fonction LTM/Mémoire) et aux lobes frontaux (LF)/Fonctions exécutives (fonction LF/Exécutive). Toutefois, il existerait une distinction critique au niveau de l’intégrité relative de ces fonctions dans ces maladies neurodégénératives, ce qui permettrait d’identifier des déficits cognitifs spécifiques à la MA, la MP et la MPD. La présente thèse s’inscrit dans cette volonté de caractériser les profils cognitifs propres à la MA, la MP et la MPD, plus précisément par l’étude novatrice de la mémoire de source et des faux souvenirs. Les quatre chapitres qui composent cette thèse servent donc à documenter la nature de ces mécanismes mnésiques, leurs patrons de performance spécifiques dans la MA, la MP et la MPD, et leur sensibilité aux atteintes des fonctions LTM/Mémoire et LF/Exécutive. Ainsi, le Chapitre I démontre la pertinence d’étudier la mémoire de source et les faux souvenirs dans la MA, la MP et la MPD, en décrivant leurs interactions avec les fonctions LTM/Mémoire et LF/Exécutive, toutes les deux atteintes dans ces maladies. Le Chapitre II, présenté sous forme d’article, révèle des déficits en mémoire de source chez des patients MP, mais seulement dans l’une des tâches employées. Également, malgré des atteintes des fonctions LF/Exécutive et LTM/Mémoire, il est démontré que seule la fonction LTM/Mémoire est liée à l’altération de la mémoire de source chez les patients MP. Le Chapitre III, également sous forme d’article, illustre un taux anormal de faux souvenirs chez des patients MA, tandis que chez des patients MP et MPD, il est démontré qu’ils ont un taux de faux souvenirs comparable à celui des participants contrôles. Il est également rapporté que malgré l’atteinte de la fonction LF/Exécutive chez les patients MA, MP et MPD, elle est seulement liée à l’augmentation des faux souvenirs chez les patients MA. Finalement, dans le dernier Chapitre (IV), les résultats obtenus sont discutés dans leur ensemble à la lumière des prédictions et connaissances actuelles, tout en identifiant les limites afin d’orienter les perspectives de recherche.In the last years, there have been numerous studies on neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease without dementia (PD) and with dementia (PDD), but differentiation of these patients based on their cognitive profile remains to be better understood. Indeed, clinical diagnosis remains difficult given that their neuropsychological deficits lack specificity. An explanation lies in the variability and overlap in terms of both clinical and neuroanatomical signs affecting similar brain regions/functions, which are those linked to medial temporal lobes (MTL)/Memory (MTL/Memory function) and to frontal lobes (FL)/Executive functions (FL/Executive function). However, a critical distinction lies in the relative integrity of both functions across AD, PD and PDD patients, which likely allows the capture of diagnosis-specific patterns of performance. This thesis addresses the need to describe the cognitive deficits more precisely by using novel measures of source memory and false memory. In the next four chapters of this thesis, the mechanisms underlying these forms of memory will be described as well as specific patterns of performance in AD, PD and PDD in source memory and false memory and their link to MTL/Memory and FL/Executive dysfunction. In Chapter I, the relevance of studying source memory and false memory in AD, PD and PDD, is explained by describing their interaction with MTL/Memory and FL/Executive functions, both impaired in these diseases. In Chapter II, a first study found source memory deficits in PD patients but only on one of the tasks that were used. Also, despite impaired MTL/Memory and FL/Executive functions, only MTL/Memory function is linked to impaired source memory in PD. In Chapter III, a second study found abnormal false memory rates in AD patients while in PD and PDD patients, false memory rates are comparable to those of healthy controls. It is also reported that despite impaired FL/Executive functions in AD, PD and PDD patients FL/Executive function is only linked to an increase in false memory rates in AD patients. Finally, in the last Chapter (IV), results of this thesis as a whole are discussed in light of predictions and the current literature and future research perspectives are discussed

Sleep habits, academic performance, and the adolescent brain structure

Here we report the first and most robust evidence about how sleep habits are associated with regional brain grey matter volumes and school grade average in early adolescence. Shorter time in bed during weekdays, and later weekend sleeping hours correlate with smaller brain grey matter volumes in frontal, anterior cingulate, and precuneus cortex regions. Poor school grade average associates with later weekend bedtime and smaller grey matter volumes in medial brain regions. The medial prefrontal anterior cingulate cortex appears most tightly related to the adolescents' variations in sleep habits, as its volume correlates inversely with both weekend bedtime and wake up time, and also with poor school performance. These findings suggest that sleep habits, notably during the weekends, have an alarming link with both the structure of the adolescent brain and school performance, and thus highlight the need for informed interventions.Peer reviewe

Green Edge ice camp campaigns : understanding the processes controlling the under-ice Arctic phytoplankton spring bloom

The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797∘ N, 63.7895∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies

Differential predictors for alcohol use in adolescents as a function of familial risk

Abstract: Traditional models of future alcohol use in adolescents have used variable-centered approaches, predicting alcohol use from a set of variables across entire samples or populations. Following the proposition that predictive factors may vary in adolescents as a function of family history, we used a two-pronged approach by first defining clusters of familial risk, followed by prediction analyses within each cluster. Thus, for the first time in adolescents, we tested whether adolescents with a family history of drug abuse exhibit a set of predictors different from adolescents without a family history. We apply this approach to a genetic risk score and individual differences in personality, cognition, behavior (risk-taking and discounting) substance use behavior at age 14, life events, and functional brain imaging, to predict scores on the alcohol use disorders identification test (AUDIT) at age 14 and 16 in a sample of adolescents (N = 1659 at baseline, N = 1327 at follow-up) from the IMAGEN cohort, a longitudinal community-based cohort of adolescents. In the absence of familial risk (n = 616), individual differences in baseline drinking, personality measures (extraversion, negative thinking), discounting behaviors, life events, and ventral striatal activation during reward anticipation were significantly associated with future AUDIT scores, while the overall model explained 22% of the variance in future AUDIT. In the presence of familial risk (n = 711), drinking behavior at age 14, personality measures (extraversion, impulsivity), behavioral risk-taking, and life events were significantly associated with future AUDIT scores, explaining 20.1% of the overall variance. Results suggest that individual differences in personality, cognition, life events, brain function, and drinking behavior contribute differentially to the prediction of future alcohol misuse. This approach may inform more individualized preventive interventions

Differential predictors for alcohol use in adolescents as a function of familial risk

Abstract: Traditional models of future alcohol use in adolescents have used variable-centered approaches, predicting alcohol use from a set of variables across entire samples or populations. Following the proposition that predictive factors may vary in adolescents as a function of family history, we used a two-pronged approach by first defining clusters of familial risk, followed by prediction analyses within each cluster. Thus, for the first time in adolescents, we tested whether adolescents with a family history of drug abuse exhibit a set of predictors different from adolescents without a family history. We apply this approach to a genetic risk score and individual differences in personality, cognition, behavior (risk-taking and discounting) substance use behavior at age 14, life events, and functional brain imaging, to predict scores on the alcohol use disorders identification test (AUDIT) at age 14 and 16 in a sample of adolescents (N = 1659 at baseline, N = 1327 at follow-up) from the IMAGEN cohort, a longitudinal community-based cohort of adolescents. In the absence of familial risk (n = 616), individual differences in baseline drinking, personality measures (extraversion, negative thinking), discounting behaviors, life events, and ventral striatal activation during reward anticipation were significantly associated with future AUDIT scores, while the overall model explained 22% of the variance in future AUDIT. In the presence of familial risk (n = 711), drinking behavior at age 14, personality measures (extraversion, impulsivity), behavioral risk-taking, and life events were significantly associated with future AUDIT scores, explaining 20.1% of the overall variance. Results suggest that individual differences in personality, cognition, life events, brain function, and drinking behavior contribute differentially to the prediction of future alcohol misuse. This approach may inform more individualized preventive interventions

Assessment of the agricultural value of sugar refinery by-products

The sugar refinery process used by Lantic Sugar Ltd generates three by-products having characteristics that give them potential as soil amendments or fertilizers, particularly as a phosphorous and calcium source. Laboratory and a field trials were conducted in order to examine the changes in agronomic properties of soil produced by the application of these residues.During the laboratory experiment, the by-products examined were spend bone char (SBC), filter-press mud (FPM), clarification scum (SCU) and a compost (COM) produced using FPM and SCU, where as in a field experiment, COM, SBC and a mixture (MIX) made of FPM and SCU, were compared to a commercial fertilizer (TSP) and non-treated soils.The orthic humic gleysol of clay texture and low pH soil conditions in which the field experiment was conducted resulted in high P fixation of all the applied residues. Contrasts analysis showed that TSP behaved as the soils unamended P for all nutrient concentrations in tissues over two cropping seasons (1993 and 1994), on two crops, namely wheat (Triticum aestivum, L.) and corn (Zea mays, L.). Treatments (residues at different rates of application) did not significantly increase the Ca levels in COM plots nor did they increase the wet aggregate stability of soil under either crop. (Abstract shortened by UMI.

Evaluation of cell salvage autotransfusion utility during liver transplantation

Background: Orthotopic liver transplantation (OLT) may be associated with massive blood loss and the need for allogenic blood product transfusions. Cell salvage autotransfusion (CS) is an attractive alternative to allogenic red blood cell (RBC) transfusion. However, controversy surrounds its usefulness during OLT; some studies stated that CS decreased transfusions of allogenic blood products and others stated that blood loss was increased. The aim of this study was to evaluate the efficiency of the CS during OLT. Patients and methods: After approval by the institutional ethics committee, a prospective survey was undertaken. A total of 150 consecutive OLTs were included in the study. Two groups of patients were formed. Period 1 included patients 1–75 with no CS use. Period 2 comprised patients 76–150 with systematic CS use. Results: Patients from both periods were comparable. CS was used in all cases in period 2, and there was enough salvaged blood to retransfuse 65% of these OLTs. The mean volume of retransfused blood was 338±339 ml. The transfusion rate did not change from period 1 to period 2. The mean number of RBC units transfused per patient was 0.4±0.9 vs 0.4±1.2 with 78.7% vs 81.3% of cases not receiving transfusion of any blood product. The threshold for RBC transfusions was the same. The length of surgery and blood loss were greater in period 2 than in period 1 (associated with the arrival of two junior surgeons), but the hemoglobin (Hb) value was also higher at the end of surgery (93.8±19.3 g/L vs 85.2±17.8 g/L, p<0.0001). Conclusion: Despite increased blood loss in period 2, CS saved 21 g/L of Hb per patient or two RBC unit transfusions. As long as we cannot predict with accuracy which patients will bleed, we will continue to use the CS for all OLTs

Effects of intraoperative hemodynamic management on postoperative acute kidney injury in liver transplantation: An observational cohort study.

BACKGROUND:Intraoperative restrictive fluid management strategies might improve postoperative outcomes in liver transplantation. Effects of vasopressors within any hemodynamic management strategy are unclear. METHODS:We conducted an observational cohort study on adult liver transplant recipients between July 2008 and December 2017. We measured the effect of vasopressors infused at admission in the intensive care unit (ICU) and total intraoperative fluid balance. Our primary outcome was 48-hour acute kidney injury (AKI) and our secondary outcomes were 7-day AKI, need for postoperative renal replacement therapy (RRT), time to extubation in the ICU, time to ICU discharge and survival up to 1 year. We fitted models adjusted for confounders using generalized estimating equations or survival models using robust standard errors. We reported results with 95% confidence intervals. RESULTS:We included 532 patients. Vasopressors use was not associated with 48-hour or 7-day AKI but modified the effects of fluid balance on RRT and mortality. A higher fluid balance was associated with a higher need for RRT (OR = 1.52 [1.15, 2.01], p<0.001 for interaction) and lower survival (HR = 1.71 [1.26, 2.34], p<0.01 for interaction) only among patients without vasopressors. In patients with vasopressors, higher doses of vasopressors were associated with a higher mortality (HR = 1.29 [1.13, 1.49] per 10 μg/min of norepinephrine). CONCLUSION:The presence of any vasopressor at the end of surgery was not associated with AKI or RRT. The use of vasopressors might modify the harmful association between fluid balance and other postoperative outcomes. The liberal use of vasopressors to implement a restrictive fluid management strategy deserves further investigation