Early-onset and late-onset Alzheimer’s disease are associated with distinct patterns of memory impairment

The goal of this study was to investigate the specific patterns of memory breakdown in patients suffering from early-onset Alzheimer’s disease (EOAD) and late-onset Alzheimer’s disease (LOAD). Twenty EOAD patients, twenty LOAD patients, twenty matched younger controls, and twenty matched older controls participated in this study. All participants underwent a detailed neuropsychological assessment, an MRI scan, an FDG-PET scan, and AD patients had biomarkers as supporting evidence of both amyloïdopathy and neuronal injury. Results of the neuropsychological assessment showed that both EOAD and LOAD groups were impaired in the domains of memory, executive functions, language, praxis, and visuoconstructional abilities, when compared to their respective control groups. EOAD and LOAD groups, however, showed distinct patterns of memory impairment. Even though both groups were similarly affected on measures of episodic, short term and working memory, in contrast semantic memory was significantly more impaired in LOAD than in EOAD patients. The EOAD group was not more affected than the LOAD group in any memory domain. EOAD patients, however, showed significantly poorer performance in other cognitive domains including executive functions and visuoconstructional abilities. A more detailed analysis of the pattern of semantic memory performance among patient groups revealed that the LOAD was more profoundly impaired, in tasks of both spontaneous recall and semantic recognition. Voxel-Based Morphometry (VBM) analyses showed that impaired semantic performance in patients was associated with reduced gray matter volume in the anterior temporal lobe region, while PET-FDG analyses revealed that poorer semantic performance was associated with greater hypometabolism in the left temporoparietal region, both areas reflecting key regions of the semantic network. Results of this study indicate that EOAD and LOAD patients present with distinct patterns of memory impairment, and that a genuine semantic impairment may represent one of the clinical hallmarks of LOAD

Alien Hand, Restless Brain: Salience Network and Interhemispheric Connectivity Disruption Parallel Emergence and Extinction of Diagonistic Dyspraxia

International audienceDiagonistic dyspraxia (DD) is by far the most spectacular manifestation reported by sufferers of acute corpus callosum (CC) injury (so-called "split-brain"). In this form of alien hand syndrome, one hand acts at cross purposes with the other "against the patient's will". Although recent models view DD as a disorder of motor control, there is still little information regarding its neural underpinnings, due to widespread connectivity changes produced by CC insult, and the obstacle that non-volitional movements represent for task-based functional neuroimaging studies. Here, we studied patient AM, the first report of DD in patient with complete developmental CC agenesis. This unique case also offers the opportunity to study the resting-state connectomics of DD in the absence of diffuse changes subsequent to CC injury or surgery. AM developed DD following status epilepticus (SE) which resolved over a 2-year period. Whole brain functional connectivity (FC) was compared (Crawford-Howell [CH]) to 16 controls during the period of acute DD symptoms (Time 1) and after remission (Time 2). Whole brain graph theoretical models were also constructed and topological efficiency examined. At Time 1, disrupted FC was observed in inter-hemispheric and intra-hemispheric right edges, involving frontal superior and midline structures. Graph analysis indicated disruption of the efficiency of salience and right frontoparietal (FP) networks. At Time 2, after remission of diagnostic dyspraxia symptoms, FC and salience network changes had resolved. In sum, longitudinal analysis of connectivity in AM indicates that DD behaviors could result from disruption of systems that support the experience and control of volitional movements and the ability to generate appropriate behavioral responses to salient stimuli. This also raises the possibility that changes to large-scale functional architecture revealed by resting-state functional magnetic resonance imaging (fMRI) (rs-fMRI) may provide relevant information on the evolution of behavioral syndromes in addition to that provided by structural and task-based functional imaging

Consensus classification of posterior cortical atrophy

INTRODUCTION: A classification framework for posterior cortical atrophy (PCA) is proposed to improve the uniformity of definition of the syndrome in a variety of research settings. METHODS: Consensus statements about PCA were developed through a detailed literature review, the formation of an international multidisciplinary working party which convened on four occasions, and a Web-based quantitative survey regarding symptom frequency and the conceptualization of PCA. RESULTS: A three-level classification framework for PCA is described comprising both syndrome- and disease-level descriptions. Classification level 1 (PCA) defines the core clinical, cognitive, and neuroimaging features and exclusion criteria of the clinico-radiological syndrome. Classification level 2 (PCA-pure, PCA-plus) establishes whether, in addition to the core PCA syndrome, the core features of any other neurodegenerative syndromes are present. Classification level 3 (PCA attributable to AD [PCA-AD], Lewy body disease [PCA-LBD], corticobasal degeneration [PCA-CBD], prion disease [PCA-prion]) provides a more formal determination of the underlying cause of the PCA syndrome, based on available pathophysiological biomarker evidence. The issue of additional syndrome-level descriptors is discussed in relation to the challenges of defining stages of syndrome severity and characterizing phenotypic heterogeneity within the PCA spectrum. DISCUSSION: There was strong agreement regarding the definition of the core clinico-radiological syndrome, meaning that the current consensus statement should be regarded as a refinement, development, and extension of previous single-center PCA criteria rather than any wholesale alteration or redescription of the syndrome. The framework and terminology may facilitate the interpretation of research data across studies, be applicable across a broad range of research scenarios (e.g., behavioral interventions, pharmacological trials), and provide a foundation for future collaborative work

Approche électrophysiologique de la mémoire de reconnaissance des patients aec troubles cognitifs légers

La Maladie d'Alzheimer (MA) est responsable du développement de nombreux déficits cognitifs dont un des plus précoces implique la mémoire de reconnaissance. Celle-ci met en jeu deux types de processus: la familiarité, processus rapide traitant des items uniques et décontextualisés, engageant les structures sous hippocampiques (cortex ento et périrhinal); et la recollection, processus plus lent nécessitant une récupération consciente du contexte de l'encodage et impliquant la formation hippocampique. Ce travail a pour but d'étudier les différences de profils électrophysiologique entre des patients souffrant de troubles cognitifs légers de type amnésique (aMCI), à risque d'évoluer vers une MA, et des sujets sains témoins lors d'une tâche de mémoire de reconnaissance, dans le but d'identifier des éléments susceptibles de définir un biomarqueur électrophysiologique fiable pour le diagnostic précoce de la MA. Un enregistrement en magnétoencéphalographie (MEG) de sept patients aMCI et de sept sujets sains agés a été réalisé lors d'une tâche de reconnaissance d'images. Nous avons étudié les réponses évoquées suite à la présentation d'images cibles correctement reconnues (condition Old) et des distracteurs correctement identifiés (conditions New). Les patients ont une activation de la région occipito-temporale gauche significativement supérieure à celle des témoins autour de 450 ms. Cette hyperactivation, se situant au sein d'une voie visuelle ventrale impliquée dans la perception, l'identification et la mémorisation des percepts, pourrait être interprétée comme le reflet d'un processus de compensation développé par les patients en réponse à un processus neurodégénératif précoceAIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocSudocFranceF

Your body and mine: A neuropsychological perspective

International audienceThe concept of ``shared representations'' suggests the existence of a common representation network between self and other. Strong support for this theory is derived from the discovery in the monkey of a population of neurons, which encode object-directed actions performed by oneself and by others. In the human, the issue of ``shared representations'' has been raised in brain-damaged studies, in particular in the setting of ``pointing to body parts'' disorders. According to the dominant view, body part designation engages a shared representation system, which encodes the visuospatial characteristics of both one's own body and the bodies of other individuals. However, the recent observation of two patients, JR and AP, with dissociated performance in pointing to body parts leads to question this model. JR presented a deficit in pointing to his own body parts, while his capacity to point to the body parts of other persons was not altered. AP exhibited the reverse pattern of impairment. Lesion study indicated a putative area of dysfunction setting in the left superior parietal lobule (SPL) in JR, and in the left inferior parietal. lobule (IPL) in AP. This double dissociation, along with two subsequent neuroimaging studies, suggests that the left SPL and IPL participate in the building of differential representations between oneself and other individuals. (C) 2008 Elsevier Masson SAS. All rights reserved

Bases représentationnelles et neurales des processus de localisation des parties du corps

Selon le modèle dominant, la désignation des parties du corps engage un système de représentations "partagées", qui encode les caractéristiques visuospatiales communes à son propre corps et à celui d'autrui. Sur la base d'une double dissociation observée chez deux sujets cérébro-lésés, nous avons émis l'hypothèse que le LPS gauche était concerné par l'analyse du corps propre et le LPI gauche par celle du corps d'autrui. Deux expérimentations en IRMF étudient ces hypothèses. La première montre que la désignation de parties du corps propre engage le LPS gauche, quel que soit le côté de la partie du corps à localiser. La deuxième expérimentation montre que la désignation de parties du corps humain engage le LPI gauche. Cette activation ne s'observe qu'en réponse à des stimuli dynamiques. L'ensemble de ces éléments suggère que les LPS et LPI gauches participent à la construction d'une représentation différentielle entre soi et autruiAIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Etude neuropathologique comparative de maladies d'Alzheimer à début précoce et tardif

AIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Traitement et reconnaissance des visages : du percept à la personne

Le traitement et la reconnaissance des visages revêtent une importance extraordinaire dans notre vie quotidienne. Ainsi, le rôle primordial des visages dans les relations inter-subjectives laisse penser que ceux-ci ne sont pas des stimuli visuels comme les autres. L'étude des patients présentant un trouble sélectif de la reconnaissance ou de l'identification des visages renforce sur des mécanismes visuo-perceptifs et mnésiques qui leur sont propres. L'état actuel des connaissances est abordé dans ce livre d'une manière pédagogique, en mettant l'accent notamment sur les concepts et articles fondamentaux. Ainsi, quatre ou cinq articles princeps sont commentés pour chaque chapitre. Le lecteur y trouvera en outre une description des outils cliniques permettant d'évaluer les différents aspects de la perception des visages, des études de cas détaillées, et une synthèse des données issues de l'imagerie fonctionnelle et de l'électrophysiologie. Les chapitres ont été rédigés par des spécialistes, dans leur propre domaine de compétence, livrant parfois leurs opinions que l'on découvre avec grand intérêt. Cet ouvrage, qui présente un panorama de l'état de l'art concernant la recherche sur les visages et les personnes, sera utile à l'ensemble de la communauté francophone des neuropsychologues, neurologues, orthophonistes, psychologues et chercheurs en neurosciences