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Neural Basis of Semantic Memory
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Book description

The advent of modern investigative techniques to explore brain function has led to major advances in understanding the neural organization and mechanisms associated with semantic memory. This book presents current theories by leading experts in the field on how the human nervous system stores and recalls memory of objects, actions, words and events. Chapters range from models of a specific domain or memory system (e.g., lexical-semantic, sensorimotor, emotion) to multiple modality accounts; from encompassing memory representations, to processing modules, to network structures, focusing on studies of both normal individuals and those with brain disease. Recent advances in neuro-exploratory techniques allow for investigation of semantic memory mechanisms noninvasively in both normal healthy individuals and patients with diffuse or focal brain damage. This has resulted in a significant increase in findings relevant to the localization and mechanistic function of brain regions engaged in semantic memory, leading to the neural models included here.

Reviews

'… the incorporation of data derived from multiple modalities of investigation and the completeness of the arguments discussed make this book a useful reference for neuroscientists involved in clinical and neurophysiological studies. Furthermore this book represents a successful first editorial attempt to approach the neural substrates of semantic memory from a 360° perspective. Even a nonexpert but motivated reader of this book will be fascinated by the most recent scientific research on where we store what we know, how we store it (e.g. with sensorimotor codes) and finally what is what we know. This book, reporting the results of different types of investigations, is strong evidence to suggest that, piece by piece, we are getting closer to solving the whole puzzle of the semantic brain.'

Source: European Neurology

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Contents

  • 1 - Semantic refractory access disorders
    pp 3-27
  • View abstract

    Summary

    This chapter examines one particular neurological syndrome, semantic refractory access dysphasia, and demonstrates that patients with this disorder can provide a window on the organization of conceptual knowledge. The first attempt to give a principled account of semantic category dissociations was by the contrast of sensory and functional attributes within the domain of animate and inanimate stimuli. The evidence of categorical dissociations derived from refractory access patients must be interpreted with caution. The chapter also examines whether semantic relatedness constitutes a general property of the organization of conceptual space or whether this property is restricted to certain semantic domains. Neuropsychological studies of the nature and organization of conceptual knowledge have tended to concentrate upon certain semantic domains more than for others. Repetitive probe experiments have also led to the proposal of information within conceptual knowledge which is spatially encoded rather than verbally or visually encoded to support geographical knowledge.
  • 2 - The anatomical locus of lesion in category-specific semantic disorders and the format of the underlying conceptual representations
    pp 28-62
  • View abstract

    Summary

    This chapter shows that format and categorical organization of semantic representations are strictly intermingled and that the study of the anatomical lesions underlying category-specific semantic disorders can contribute to clarifying the nature of these intimate relationships. It determines whether the anatomical locus of lesion is different in patients with a category-specific impairment for action names and object names and whether the neuroanatomical correlates of these category-specific disorders are consistent with the predictions based on the sensorymotor model of semantic knowledge. The chapter focuses on predictions based on the sensory-functional and the domains of knowledge hypothesis, rather than on those based on the intercorrelations among semantic features hypothesis, since the latter assumes that the severity of brain damage plays the major role in the pathophysiology of category-specific disorders. It presents the results of investigations which have checked the neuroanatomical predictions of the intercorrelations among semantic features hypothesis.
  • 3 - Functional modularity of semantic memory revealed by event-related brain potentials
    pp 65-104
  • View abstract

    Summary

    This chapter demonstrates how event-related potentials (ERPs) can be used to detect, isolate, and analyze functional neural modules, with special attention to functional modularity in semantic information processing. In particular, it shows how a new method of analyzing electrophysiological data, the additive-amplitude method, combines the physical property of linear superposition of electrical fields with factorial experimental design to reveal the existence of encapsulated neurocognitive modules without relying on strong assumptions. The fact that ERPs can be measured at the scalp indicates that the conditions of synchrony, spatial proximity, and parallel geometrical configuration that enable the summation of individual neuronal electric fields must hold. The additive-amplitude method yields new insights into semantic information processing architecture. Finally, it should be noted that because the additive-amplitude method focuses on a fundamental property of mind and brain, it is applicable to a broad range of areas within psychology and neuroscience.
  • 4 - Bilingual semantic memory revisited – ERP and fMRI evidence
    pp 105-130
  • View abstract

    Summary

    The psycholinguistic experimental methodologies and measures such as event-related brain potentials (ERPs) and functional magnetic resonance imaging (fMRI) are increasingly used in the investigation of bilingual language processing. These methods now allow us to model the actual representations and neural basis of bilingual semantic memory based on Weinreich's initial typologies, expanding the typologies to refer to mental representations. There have also been several studies addressing bilingual semantic memory that have appealed to sentence-level processing without necessarily using the violation paradigm. The discussion of fMRI data augments our understanding of the aspects of semantic memory representation and access that have been established so far with behavioral and electrophysiological data. Only a few bilingual neuroimaging studies have directly tested the convergence hypothesis for semantic memory, i.e. the theory that L2 processing becomes more and more L1-like with increased L2 proficiency.
  • 5 - Schizophrenia and semantic memory
    pp 133-146
  • View abstract

    Summary

    Formal thought disorder (FTD) is a debilitating symptom that affects 90 percent of schizophrenic patients and undermines a patient's capacity to communicate. This chapter reviews the clinical and cognitive symptoms related to (FTD), the evidence available that supports different aspects of semantic impairments in FTD, and recent data suggesting that a far-spreading activation theory within the semantic system is the core, underlying deficit resulting in FTD. The Thought, Language and Communication Scale (TLC) provided the first standardized tool that quantified positive FTD severity which in turn enhanced FTD research. An early neuroimaging study used positron emission tomography (PET) to evaluate the relationship between regional blood flow and symptomatology of 30 schizophrenia patients during a resting state. Based on the suggested role of semantic memory dysfunction in the pathophysiology of FTD, the chapter examines whether a specific semantic memory operation is more relevant to this symptomatology.
  • 6 - Effects of word imageability on semantic access: neuroimaging studies
    pp 149-181
  • View abstract

    Summary

    Dual coding theory proposes that abstract concepts are encoded and stored in memory in the form of symbolic or verbal representations, whereas concrete concepts are dually encoded into memory as both verbal representations and image codes grounded in perceptual experience. This chapter describes the three recent event-related functional magnetic resonance imaging (fMRI) experiments in which word imageability was manipulated during visual lexical decision, semantic decision, and word naming tasks. It attempts to resolve some of the inconsistencies in the imaging literature by using relatively large samples of participants and large numbers of items to ensure reliable activation patterns, by careful matching of concrete and abstract items on all possible nuisance variables, and by matching as closely as possible the task demands for the concrete and abstract conditions. The results were remarkably consistent across studies and provide clear support for some of the basic tenets of the dual-coding model.
  • 7 - The neural systems processing tool and action semantics
    pp 182-204
    • By Uta Noppeney, Max-Planck-Institute for Biological Cybernetics
  • View abstract

    Summary

    This chapter discusses the contributions of functional imaging to our understanding of how action and tool concepts are represented and processed in the human brain. It is framed within the feature-based account of semantic memory. This approach assumes that conceptual knowledge is represented in a large distributed network, indexing a range of semantic features. Neurophysiological studies in non-human primates have suggested that the frontoparietal circuitry may play a role in visuomotor transformations and action matching, imitation and understanding. Studies of action observation and semantic retrieval provide converging evidence that left posterior middle temporal gyrus (LPMT) activation is commonly increased for hand manipulation and whole-body movements. The chapter revisits several themes that have emerged from functional imaging studies of tool and action processing. It evaluates the positive evidence for the feature-based account of semantic memory, and concludes by highlighting future directions to investigate the neural mechanisms of tool and action processing.
  • 8 - The semantic representation of nouns and verbs
    pp 205-216
  • View abstract

    Summary

    The sensory/functional theory (SFT) was originally motivated by a series of remarkable observations about the neurobiology of language production. Some case series have shown that the manipulation of imageability affects performance on noun and verb production tasks only for a subset of patients suggesting that the extended sensory/functional theory (ESFT) is not adequate to explain many cases of impairment in noun or verb naming. A different variation on the theme of the SFT maintains that nouns and verbs differ primarily not in the proportion of functional or nonperceptual information with which they are associated, but in the kind of sensory information by which they are prototypically defined. Some evidence consistent with the idea that the categorization of words as nouns or verbs depends on a core semantic structure comes from a recent study using event-related functional magnetic resonance imaging (fMRI) with English speaking subjects.
  • 9 - Role of the basal ganglia in language and semantics: supporting cast
    pp 219-244
  • View abstract

    Summary

    This chapter describes the basal ganglia organization and endeavors to develop a conceptual framework for understanding how the basal ganglia impact semantic and related language functions. At the most general level of discussion, the basal ganglia can be best understood through their role in intention and attention. Actions and cognitions are enhanced through the direct loop of the basal ganglia. Enhancement is modulated by D1 receptor activity, which has the effect of facilitating and prolonging the enhancement. Semantic priming studies hold great promise for continuing to unravel the impact of basal ganglia functions on semantics. The chapter concludes that more research will lead to a greater understanding of how basal ganglia functions influence semantic and other cognitive functions. It will help us to manage or even mitigate the cognitive deficits that occur in Parkinson's disease, in lesions of the basal ganglia, or in other basal ganglia dysfunctions.
  • Part 10 - Process and content in semantic memory
    pp 247-264
  • View abstract

    Summary

    Semantic content knowledge and ability to process that knowledge are both necessary. Theories of semantic memory have tended to focus on knowledge content. Semantic memory impairments in patients with neurodegenerative diseases, manifested in difficulties naming, recognizing, or describing objects, are well documented. Neurologically healthy individuals, including the elderly, are able to appropriately use similarity-or rule-based categorization, both in daily functioning and in controlled studies. This chapter details some work investigating semantic knowledge and semantic categorization processes. The novel animal categorization task was designed to separate content from process and to relate the findings to semantic memory. Processing matters and it may be that category-specific deficits arise because different categories are more or less conducive to particular categorization processes, which can be selectively compromised. Additionally, knowledge of the diagnostic status of features, as well as executive resources, appears to be a necessary component of rule-based processing.
  • 11 - The conceptual structure account: A cognitive model of semantic memory and its neural instantiation
    pp 265-301
  • View abstract

    Summary

    The investigation of the neuroanatomical bases of semantic memory is in its infancy. This chapter describes the Conceptual Structure Account (CSA), a cognitive model developed at the Centre for Speech, Language and the Brain. It presents the results of neuropsychological studies with patients and healthy volunteers that have tested the main claims of this model. The chapter investigates the neural instantiation of the CSA using functional imaging techniques. The CSA generates a number of predictions about the kinds of information and types of processes that will be impaired and spared in patients with category specific semantic impairments. The chapter addresses the studies attempting to tap automatic semantic processing, as untimed tasks or paradigms which elicit controlled processing may emphasize cognitive processes taking place outside the semantic system. Activity associated with the basic-level naming of living compared to nonliving things was centered in the entorhinal cortex medial to the perirhinal cortex.
  • 12 - Neural foundations for conceptual representations: Evidence from functional brain imaging
    pp 302-330
  • View abstract

    Summary

    This chapter focuses on one aspect of the functional neuroanatomy of semantic memory. It outlines a model of how conceptual knowledge about concrete entities (objects) is organized in the brain based on functional brain imaging studies of normal, intact individuals, and provides an overview of findings from functional brain imaging studies. The chapter also discusses a series of studies aimed at addressing particular questions and concerns about the organization of conceptual knowledge in the brain as revealed by functional brain imaging. In addition to the studies and evidence discussed in the chapter, findings from a large number of laboratories have provided evidence for other examples of domain-specificity in this region of the brain. This work includes studies showing that a region of the parahippocampal cortex is particularly responsive to depictions of places (outdoor scenes, buildings) and, on a more conceptual level, to objects strongly associated with spatial contexts.
  • 13 - Neural hybrid model of semantic object memory (version 1.1)
    pp 331-360
  • View abstract

    Summary

    With the intended goal of the model to account for semantic memory storage and processing at a neurophysiological level, the neural hybrid model of semantic memory (version 1. 1) represents a mechanistic account of semantic memory given the evidence available, with the limitations of current investigative techniques, their inherent assumptions, and shortcomings. The visual memory system is one of the most extensively studied for object memory organization. The neural hybrid model advocates the concept of distinct neural encodings for category-based and/or feature-based semantic knowledge representations that exist in separate systems in various sensory, motor, lexicalsemantic and limbic domains. The chapter proposes a neural mechanism by which components of an object from multiple modalities represented at separated sites within the brain can be bound to form an integrated object memory. This synchronous co-activation is mediated by the thalamus via 30 Hz oscillating rhythms.

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