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      Semantic word category processing in semantic dementia and posterior cortical atrophy

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          Abstract

          There is general agreement that perisylvian language cortex plays a major role in lexical and semantic processing; but the contribution of additional, more widespread, brain areas in the processing of different semantic word categories remains controversial. We investigated word processing in two groups of patients whose neurodegenerative diseases preferentially affect specific parts of the brain, to determine whether their performance would vary as a function of semantic categories proposed to recruit those brain regions. Cohorts with (i) Semantic Dementia (SD), who have anterior temporal-lobe atrophy, and (ii) Posterior Cortical Atrophy (PCA), who have predominantly parieto-occipital atrophy, performed a lexical decision test on words from five different lexico-semantic categories: colour (e.g., yellow), form ( oval), number ( seven), spatial prepositions ( under) and function words ( also). Sets of pseudo-word foils matched the target words in length and bi-/tri-gram frequency. Word-frequency was matched between the two visual word categories (colour and form) and across the three other categories (number, prepositions, and function words). Age-matched healthy individuals served as controls. Although broad word processing deficits were apparent in both patient groups, the deficit was strongest for colour words in SD and for spatial prepositions in PCA. The patterns of performance on the lexical decision task demonstrate (a) general lexicosemantic processing deficits in both groups, though more prominent in SD than in PCA, and (b) differential involvement of anterior-temporal and posterior-parietal cortex in the processing of specific semantic categories of words.

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          Conceptual representations in mind and brain: theoretical developments, current evidence and future directions.

          Conceptual representations in long-term memory crucially contribute to perception and action, language and thought. However, the precise nature of these conceptual memory traces is discussed controversially. In particular, the grounding of concepts in the sensory and motor brain systems is the focus of a current debate. Here, we review theoretical accounts of the structure and neural basis of conceptual memory and evaluate them in light of recent empirical evidence. Models of conceptual processing can be distinguished along four dimensions: (i) amodal versus modality-specific, (ii) localist versus distributed, (iii) innate versus experience-dependent, and (iv) stable versus flexible. A systematic review of behavioral and neuroimaging studies in healthy participants along with brain-damaged patients will then be used to evaluate the competing theoretical approaches to conceptual representations. These findings indicate that concepts are flexible, distributed representations comprised of modality-specific conceptual features. Conceptual features are stored in distinct sensory and motor brain areas depending on specific sensory and motor experiences during concept acquisition. Three important controversial issues are highlighted, which require further clarification in future research: the existence of an amodal conceptual representation in the anterior temporal lobe, the causal role of sensory and motor activation for conceptual processing and the grounding of abstract concepts in perception and action. We argue that an embodiment view of conceptual representations realized as distributed sensory and motor cell assemblies that are complemented by supramodal integration brain circuits may serve as a theoretical framework to guide future research on concrete and abstract concepts. Copyright © 2011 Elsevier Srl. All rights reserved.
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            Structure and deterioration of semantic memory: a neuropsychological and computational investigation.

            Wernicke (1900, as cited in G. H. Eggert, 1977) suggested that semantic knowledge arises from the interaction of perceptual representations of objects and words. The authors present a parallel distributed processing implementation of this theory, in which semantic representations emerge from mechanisms that acquire the mappings between visual representations of objects and their verbal descriptions. To test the theory, they trained the model to associate names, verbal descriptions, and visual representations of objects. When its inputs and outputs are constructed to capture aspects of structure apparent in attribute-norming experiments, the model provides an intuitive account of semantic task performance. The authors then used the model to understand the structure of impaired performance in patients with selective and progressive impairments of conceptual knowledge. Data from 4 well-known semantic tasks revealed consistent patterns that find a ready explanation in the model. The relationship between the model and related theories of semantic representation is discussed.
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              How neurons make meaning: brain mechanisms for embodied and abstract-symbolic semantics.

              How brain structures and neuronal circuits mechanistically underpin symbolic meaning has recently been elucidated by neuroimaging, neuropsychological, and neurocomputational research. Modality-specific 'embodied' mechanisms anchored in sensorimotor systems appear to be relevant, as are 'disembodied' mechanisms in multimodal areas. In this paper, four semantic mechanisms are proposed and spelt out at the level of neuronal circuits: referential semantics, which establishes links between symbols and the objects and actions they are used to speak about; combinatorial semantics, which enables the learning of symbolic meaning from context; emotional-affective semantics, which establishes links between signs and internal states of the body; and abstraction mechanisms for generalizing over a range of instances of semantic meaning. Referential, combinatorial, emotional-affective, and abstract semantics are complementary mechanisms, each necessary for processing meaning in mind and brain. Copyright © 2013 Elsevier Ltd. All rights reserved.
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                Author and article information

                Contributors
                Journal
                Cortex
                Cortex
                Cortex; a Journal Devoted to the Study of the Nervous System and Behavior
                Masson
                0010-9452
                1973-8102
                1 August 2017
                August 2017
                : 93
                : 92-106
                Affiliations
                [a ]Medical Research Council, Cognition and Brain Sciences Unit, Cambridge, UK
                [b ]Linguistics Department, College of Humanities and Social Sciences, United Arab Emirates University, United Arab Emirates
                [c ]Department of Clinical Neurosciences, University of Cambridge, UK
                [d ]German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany
                [e ]Tecnalia Research and Innovation Center, Health Division, Neurotechnology Unit, Bizkaia Technology Park, Derio, Spain
                [f ]Brain Language Laboratory, Department of Philosophy and Humanities, WE4, Freie Universität Berlin, Berlin, Germany
                [g ]Berlin School of Mind and Brain, Humboldt Universität zu Berlin, Berlin, Germany
                [h ]Einstein Center for Neurosciences, Berlin, Germany
                Author notes
                [] Corresponding author. Linguistics Department, College of Humanities and Social Sciences, P.O. Box 15551, Al-Ain, United Arab Emirates.Linguistics DepartmentCollege of Humanities and Social SciencesP.O. Box 15551Al-AinUnited Arab Emirates zubaida.shebani@ 123456uaeu.ac.ae
                [∗∗ ] Corresponding author. Brain Language Laboratory, Department of Philosophy and Humanities, WE4, Freie Universität Berlin, Habelschwerdter Allee 45, 14195 Berlin, Germany.Brain Language LaboratoryDepartment of Philosophy and HumanitiesWE4Freie Universität BerlinHabelschwerdter Allee 45Berlin14195Germany f.p@ 123456fu-berlin.de
                Article
                S0010-9452(17)30133-8
                10.1016/j.cortex.2017.04.016
                5542041
                28624681
                f35d58cf-3b73-4feb-941b-25de9f17dcf5
                © 2017 The Authors

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                Categories
                Research Report

                Neurology
                semantic dementia,posterior cortical atrophy,category specificity,word processing,semantics

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