Is a plum a memory problem? Longitudinal study of the reversal of concreteness effect in a patient with semantic dementia

Reversal of the concreteness effect can be detected in the natural speech of older adults with amnestic, but not non-amnestic, mild cognitive impairment

INTRODUCTION

Patients with Alzheimer's disease present with difficulty in lexical retrieval and reversal of the concreteness effect in nouns. Little is known about the phenomena before the onset of symptoms. We anticipate early linguistic signs in the speech of people who suffer from amnestic mild cognitive impairment (MCI). Here, we report the results of a corpus-linguistic approach to the early detection of cognitive impairment.

METHODS

One hundred forty-eight English-speaking Singaporeans provided natural speech data, on topics of their choice; 74 were diagnosed with single-domain MCI (38 amnestic, 36 non-amnestic), 74 cognitively healthy. The recordings yield 267,310 words, which are tagged for parts of speech. We calculate the per-minute word counts and concreteness scores of all tagged words, nouns, and verbs in the dataset.

RESULTS

Compared to controls, subjects with amnestic MCI produce fewer but more abstract nouns. Verbs are not affected.

DISCUSSION

Slower retrieval of nouns and the reversal of the concreteness effect in nouns are manifested in natural speech and can be detected early through corpus-based analysis.

Highlights

Reversal of the concreteness effect is manifested in patients with Alzheimer's disease (AD) and semantic dementia.The paper reports a corpus-based analysis of natural speech by people with amnestic and non-amnestic mild cognitive impairment (MCI) and cognitively healthy controls.People with amnestic MCI produce fewer and more abstract nouns than people with non-amnestic MCI and healthy controls. Verbs appear to be unaffected.The imageability problem can be detected in natural everyday speech by people with amnestic MCI, which carries a higher risk of conversion to AD.

Concrete and Abstract Concepts in Primary Progressive Aphasia and Alzheimer's Disease: A Scoping Review

The concreteness effect (CE), namely a better performance with concrete compared to abstract concepts, is a constant feature in healthy people, and it usually increases in persons with aphasia (PWA). However, a reversal of the CE has been reported in patients affected by the semantic variant of Primary Progressive Aphasia (svPPA), a neurodegenerative disease characterized by anterior temporal lobe (ATL) atrophy. The present scoping review aims at identifying the extent of evidence regarding the abstract/concrete contrast in Alzheimer's disease (AD) and svPPA and associated brain atrophy. Five online databases were searched up to January 2023 to identify papers where both concrete and abstract concepts were investigated. Thirty-one papers were selected and showed that while in patients with AD, concrete words were better processes than abstract ones, in most svPPA patients, there was a reversal of the CE, with five studies correlating the size of this effect with ATL atrophy. Furthermore, the reversal of CE was associated with category-specific impairments (living things) and with a selective deficit of social words. Future work is needed to disentangle the role of specific portions of the ATL in concept representation.

Investigating the influence of semantic factors on word retrieval: Reservations, results and recommendations

There is consensus that word retrieval starts with activation of semantic representations. However, in adults without language impairment, relatively little attention has been paid to the effects of the semantic attributes of to-be-retrieved words. This paper, therefore, addresses the question of which item-inherent semantic factors influence word retrieval. Specifically, it reviews the literature on a selection of these factors: imageability, concreteness, number of semantic features, typicality, intercorrelational density, featural distinctiveness, concept distinctiveness, animacy, semantic neighbourhood density, semantic similarity, operativity, valence, and arousal. It highlights several methodological challenges in this field, and has a focus on the insights from studies with people with aphasia where the effects of these variables are more prevalent. The paper concludes that further research simultaneously examining the effects of different semantic factors that are likely to affect lexical co-activation, and the interaction of these variables, would be fruitful, as would suitably scaled computational modelling of these effects in unimpaired language processing and in language impairment. Such research would enable the refinement of theories of semantic processing and word production, and potentially have implications for diagnosis and treatment of semantic and lexical impairments.

Exploring Abstract Semantic Associations in the Frontotemporal Dementia Spectrum in a Dutch Population

OBJECTIVE

To investigate the differential ability of the "Test Relaties Abstracte Concepten" (TRACE), a Dutch test for abstract semantic knowledge, in frontotemporal dementia (FTD).

METHODS

The TRACE was administered in patients with behavioral variant FTD (bvFTD; n = 16), nonfluent variant (nfvPPA; n = 10), logopenic variant (lvPPA; n = 10), and semantic variant primary progressive aphasia (svPPA; n = 9), and controls (n = 59). We examined group differences, performed correlational analyses with other neuropsychological tests and investigated discriminative ability. We compared the TRACE with a semantic association test for concrete stimuli (SAT).

RESULTS

All patient groups, except nfvPPA, performed worse on the TRACE than controls (p < .01). svPPA patients performed worse than the other patient groups (p < .05). The TRACE discriminated well between patient groups, except nfvPPA, versus controls (all p < .01) and between svPPA versus other patient groups with high sensitivity (75-100%) and specificity (86%-92%). In bvFTD and nfvPPA the TRACE correlated with language tests (ρ > 0.6), whereas in svPPA the concrete task correlated (ρ ≥ 0.75) with language tests. Patients with bvFTD, nfvPPA and lvPPA performed lower on the TRACE than the SAT (p < .05), whereas patients with svPPA were equally impaired on both tasks (p = .2).

DISCUSSION

We demonstrated impaired abstract semantic knowledge in patients with bvFTD, lvPPA, and svPPA, but not nfvPPA, with svPPA patients performing worse than the other subtypes. The TRACE was a good classifier between each patient group versus controls and between svPPA versus other patient groups. This highlights the value of incorporating semantic tests with abstract stimuli into standard neuropsychological assessment for early differential diagnosis of FTD subtypes.

The neural correlates of abstract and concrete words

In this chapter, the literature concerning the dissociation between concrete and abstract words is reviewed, with a specific focus on the role of the temporal lobes. A number of studies have demonstrated the so-called "concreteness effect," that is, the superior processing of concrete versus abstract words. However, some neuropsychological patients have been described with a reversal of concreteness effect, namely, a better performance with abstract than concrete words. Available data suggest that the most frequent causes of this reversed effect are herpes simplex encephalitis and semantic dementia, which typically affect bilaterally anterior temporal regions. Direct electrical stimulation of the left temporal pole further supports this correlation, while the neuroimaging literature is more controversial. In fact, data from neuroimaging studies show either that abstract and concrete noun processing at least partly relies on the activation of a common left-lateralized network, or that abstract word processing is supported by the activation of networks within the left inferior frontal gyrus and the middle temporal gyrus. In between abstract and concrete concepts are idioms, which are represented by concrete actions conveying abstract mental states and events. The involvement of the temporal lobes in processing this particular figure of language is discussed.

An ALE meta-analytical review of the neural correlates of abstract and concrete words

Several clinical studies have reported a double dissociation between abstract and concrete concepts, suggesting that they are processed by at least partly different networks in the brain. However, neuroimaging data seem not in line with neuropsychological reports. Using the ALE method, we run a meta-analysis on 32 brain-activation imaging studies that considered only nouns and verbs. Five clusters were associated with concrete words, four clusters with abstract words. When only nouns were selected three left activation clusters were found to be associated with concrete stimuli and only one with abstract nouns (left IFG). These results confirm that concrete and abstract words processing involves at least partially segregated brain areas, the IFG being relevant for abstract nouns and verbs while more posterior temporoparietal-occipital regions seem to be crucial for processing concrete words, in contrast with the neuropsychological literature that suggests a temporal anterior involvement for concrete words. We investigated the possible reasons that produce different outcomes in neuroimaging and clinical studies.

Automated analysis of lexical features in frontotemporal degeneration

We implemented an automated analysis of lexical aspects of semi-structured speech produced by healthy elderly controls (n = 37) and three patient groups with frontotemporal degeneration (FTD): behavioral variant FTD (n = 74), semantic variant primary progressive aphasia (svPPA, n = 42), and nonfluent/agrammatic PPA (naPPA, n = 22). Based on previous findings, we hypothesized that the three patient groups and controls would differ in the counts of part-of-speech (POS) categories and several lexical measures. With a natural language processing program, we automatically tagged POS categories of all words produced during a picture description task. We further counted the number of wh-words, and we rated nouns for abstractness, ambiguity, frequency, familiarity, and age of acquisition. We also computed the cross-entropy estimation, where low cross-entropy indicates high predictability, and lexical diversity for each description. We validated a subset of the POS data that were automatically tagged with the Google Universal POS scheme using gold-standard POS data tagged by a linguist, and we found that the POS categories from our automated methods were more than 90% accurate. For svPPA patients, we found fewer unique nouns than in naPPA and more pronouns and wh-words than in the other groups. We also found high abstractness, ambiguity, frequency, and familiarity for nouns and the lowest cross-entropy estimation among all groups. These measures were associated with cortical thinning in the left temporal lobe. In naPPA patients, we found increased speech errors and partial words compared to controls, and these impairments were associated with cortical thinning in the left middle frontal gyrus. bvFTD patients' adjective production was decreased compared to controls and was correlated with their apathy scores. Their adjective production was associated with cortical thinning in the dorsolateral frontal and orbitofrontal gyri. Our results demonstrate distinct language profiles in subgroups of FTD patients and validate our automated method of analyzing FTD patients' speech.

Automated analysis of lexical features in Frontotemporal Degeneration

We implemented an automated analysis of lexical aspects of semi-structured speech produced by healthy elderly controls (n=37) and three patient groups with frontotemporal degeneration (FTD): behavioral variant FTD (n=74), semantic variant primary progressive aphasia (svPPA, n=42), and nonfluent/agrammatic PPA (naPPA, n=22). Based on previous findings, we hypothesized that the three patient groups and controls would differ in the counts of part-of-speech (POS) categories and several lexical measures. With a natural language processing program, we automatically tagged POS categories of all words produced during a picture description task. We further counted the number of wh -words, and we rated nouns for abstractness, ambiguity, frequency, familiarity, and age of acquisition. We also computed the cross-entropy estimation, which is a measure of word predictability, and lexical diversity for each description. We validated a subset of the POS data that were automatically tagged with the Google Universal POS scheme using gold-standard POS data tagged by a linguist, and we found that the POS categories from our automated methods were more than 90% accurate. For svPPA patients, we found fewer unique nouns than in naPPA and more pronouns and wh -words than in the other groups. We also found high abstractness, ambiguity, frequency, and familiarity for nouns and the lowest cross-entropy estimation among all groups. These measures were associated with cortical thinning in the left temporal lobe. In naPPA patients, we found increased speech errors and partial words compared to controls, and these impairments were associated with cortical thinning in the left middle frontal gyrus. bvFTD patients' adjective production was decreased compared to controls and was correlated with their apathy scores. Their adjective production was associated with cortical thinning in the dorsolateral frontal and orbitofrontal gyri. Our results demonstrate distinct language profiles in subgroups of FTD patients and validate our automated method of analyzing FTD patients' speech.

Dissociating action and abstract verb comprehension post-stroke

The neural bases of action and abstract concept representations remain a topic of debate. While several lines of research provide evidence for grounding of action-related conceptual content into sensory-motor systems, results of traditional lesion-deficit studies have been somewhat inconsistent. Further, few studies have directly compared the neural substrates of action and relatively abstract verb comprehension post-stroke. Here, we investigated the impact of the disruption of two neural networks on comprehension of action and relatively abstract verbs in 48 unilateral left-hemisphere stroke patients using two methodologies: 1) lesion-deficit association and 2) resting-state functional connectivity (RSFC) analyses. Disruption of RSFC between the left inferior frontal gyrus and right hemisphere primary and secondary sensory-motor areas predicted greater relative impairment of action semantics. Voxel-based lesion-symptom mapping revealed that damage to frontal white matter, extending towards the inferior frontal gyrus, also predicted greater relative impairment of action semantics. On the other hand, damage to the left anterior middle temporal gyrus significantly impaired the more abstract category relative to action. These findings support the view that action and non-action/abstract semantic processing rely on partially dissociable brain networks, with action concepts relying more heavily on sensory-motor areas. The results also have wider implications for lesion-deficit association studies and show how the contralateral hemisphere can play a compensatory role following unilateral stroke.

Efecto de concretud inverso en Afasia Progresiva Primaria-variante semántica: Estudio longitudinal de un paciente

La Afasia Progresiva Primaria (APP) es una patología neurodegenerativa que se presenta con afectación insidiosa y progresiva del lenguaje. Los criterios diagnósticos actuales diferencian tres subtipos de APP, cada una con perfiles neurolingüísticos específicos. Diversas investigaciones han propuesto que un síntoma característico de la APP variante semántica (APP-vs) es un mayor compromiso en el procesamiento de conceptos concretos que de abstractos (Efecto de Concretud Inverso - ECI). Para explicar este ECI se han propuesto diferentes explicaciones: (a). el patrón de compromiso neural, (b). el nivel educativo de los pacientes, (c). el estadio de la enfermedad. El objetivo del presente trabajo es estudiar en forma longitudinal la progresión en el procesamiento de conceptos concretos y abstractos en un paciente diagnosticado con APP-vs. Para ello se utilizó una tarea de juicios de sinonimia donde se debe identificar si dos palabras son sinónimos o no. La tarea cuenta con pares de conceptos concretos y abstractos. Se evaluó al paciente en tres momentos (2014, 2015 y 2016). Se observó un mejor desempeño de conceptos abstractos en la primera evaluación. El ECI desaparece en la segunda evaluación. El patrón se revierte en la tercera. Estos resultados apoyan la propuesta de que el ECI observado en pacientes con APP-vs es un síntoma de los estadios iniciales de la enfermedad. Este ECI se relacionaría con la afectación temprana de las porciones del Lóbulo Temporal Anterior que procesan rasgos visuales, que serían más relevantes para los conceptos concretos.

Primary Progressive Aphasia and Stroke Aphasia

PURPOSE OF REVIEW

This article summarizes the clinical and anatomic features of the three named variants of primary progressive aphasia (PPA): semantic variant PPA, nonfluent/agrammatic variant PPA, and logopenic variant PPA. Three stroke aphasia syndromes that resemble the PPA variants (Broca aphasia, Wernicke aphasia, and conduction aphasia) are also presented.

RECENT FINDINGS

Semantic variant PPA and Wernicke aphasia are characterized by fluent speech with naming and comprehension difficulty; these syndromes are associated with disease in different portions of the left temporal lobe. Patients with nonfluent/agrammatic variant PPA or Broca aphasia have nonfluent speech with grammatical difficulty; these syndromes are associated with disease centered in the left inferior frontal lobe. Patients with logopenic variant PPA or conduction aphasia have difficulty with repetition and word finding in conversational speech; these syndromes are associated with disease in the left inferior parietal lobe. While PPA and stroke aphasias resemble one another, this article also presents their distinguishing features.

SUMMARY

Primary progressive and stroke aphasia syndromes interrupt the left perisylvian language network, resulting in identifiable aphasic syndromes.

Identification of taxonomic and thematic relationships: Do the two semantic systems have the same status in semantic dementia?

Introduction: Disequilibrium between the taxonomic and thematic semantic systems was previously hypothesized in participants with semantic dementia (SD), without rigorously assessing their ability to identify the two types of semantic relationships. Therefore, the aim of the present study was to directly compare the ability of 10 participants with SD, 10 participants with Alzheimer's disease (AD), and 20 controls to identify thematic versus taxonomic relationships. Methods: Participants performed an explicit forced-choice picture-matching task in which they had to determine which of two pictures of choice was semantically related to the target picture. Target pictures could display natural or artifact objects. Each target was presented once with a taxonomically related picture and once with a thematically related picture. Results: Analyses of correct thematic and taxonomic matches as a function of target domain showed that the performance of the two groups of patients differed in the taxonomic conditions but not in the thematic conditions, demonstrating a relative preservation of thematic knowledge in SD. Additional correlation analyses further indicated that the particular status of thematic relationships in SD was even stronger for artifact concepts. Conclusions: Results provide evidence of the heterogeneous nature of semantic knowledge disruption in SD, and could be regarded as being consistent with the existence of two neuroanatomically and functionally distinct semantic systems. Results further stress the relevance of performing a more detailed and complete assessment of semantic performance in participants with SD, in order to capture the impaired but also preserved aspects of their knowledge.

Longitudinal Changes in Semantic Concreteness in Semantic Variant Primary Progressive Aphasia (svPPA)

This study examines longitudinal changes in the concreteness of nouns produced by human patients with semantic variant primary progressive aphasia (svPPA). Cross-sectional studies show that patients with svPPA demonstrate severe loss of concrete noun knowledge linked to atrophy of the left ventral temporal lobe. It is unknown how disease spread and duration affect the magnitude of the concreteness impairment in svPPA. We evaluate longitudinal spoken production of concrete nouns in svPPA, and relate this to changes in longitudinal MRI measures of gray matter (GM). Noun concreteness in svPPA is compared to that of behavioral variant frontotemporal dementia (bvFTD) patients, who typically demonstrate highly concrete speech. We elicited naturalistic speech samples at two time points (time 1 and time 2) in patients with svPPA (n = 11) and bvFTD (n = 15) through descriptions of the Cookie Theft picture and evaluated each spoken noun for concreteness. Compared to bvFTD patients whose noun production remained highly concrete throughout the testing period, mixed-effects models revealed that noun concreteness significantly decreased as disease progressed in svPPA. We also measured longitudinal changes to GM in a subset of svPPA patients (n = 7), who showed significant decline in the left and right temporal and frontal regions. Regression analyses revealed that longitudinal GM atrophy in the right fusiform and parahippocampal gyri and the left superior temporal gyrus was related to decreasing noun concreteness. These results suggest that progressive atrophy of the ventral temporal lobe in svPPA contributes to declining concrete noun production over time.

Investigating the functional neuroanatomy of concrete and abstract word processing through direct electric stimulation (DES) during awake surgery

Neuropsychological, neuroimaging and electrophysiological studies demonstrate that abstract and concrete word processing relies not only on the activity of a common bilateral network but also on dedicated networks. The neuropsychological literature has shown that a selective sparing of abstract relative to concrete words can be documented in lesions of the left anterior temporal regions. We investigated concrete and abstract word processing in 10 patients undergoing direct electrical stimulation (DES) for brain mapping during awake surgery in the left hemisphere. A lexical decision and a concreteness judgment task were added to the neuropsychological assessment during intra-operative monitoring. On the concreteness judgment, DES delivered over the inferior frontal gyrus significantly decreased abstract word accuracy while accuracy for concrete words decreased when the anterior temporal cortex was stimulated. These results are consistent with a lexical-semantic model that distinguishes between concrete and abstract words related to different neural substrates in the left hemisphere.

Procesamiento semántico de conceptos concretos y abstractos en Afasia Progresiva Primaria-variante semántica

La Afasia Progresiva Primaria-variante semántica (APP-vs) se caracteriza por la afectación progresiva del conocimiento conceptual. Algunas investigaciones han reportado la mayor afectación de los conceptos abstractos en relación con los concretos, es decir, un efecto de concretud. No obstante, otros investigadores dan cuenta de un efecto de concretud inverso, es decir, un mejor desempeño con conceptos abstractos en relación con concretos. En esta investigación se compara el desempeño, por medio en una tarea de juicios de sinonimia, de un grupo de 8 pacientes diagnosticados con APP-vs y un grupo de 20 controles emparejados en edad y nivel educativo. Los resultados dan cuenta de un efecto de concretud, es decir, un mejor desempeño con conceptos concretos tanto con sustantivos como con verbos. Estos hallazgos se alinean con las investigaciones previas en las que se detecta un peor rendimiento de los pacientes con APP-vs con conceptos abstractos. El efecto de concretud encontrado apoyaría la hipótesis de un centro semántico amodal relevante para el procesamiento de conceptos concretos y abstractos. La menor afectación de los conceptos concretos observada podría explicarse por su mayor riqueza semántica.

Linguistic Aspects of Primary Progressive Aphasia

Primary progressive aphasia (PPA) refers to a disorder of declining language associated with neurodegenerative diseases such as frontotemporal degeneration and Alzheimer disease. Variants of PPA are important to recognize from a medical perspective because these syndromes are clinical markers suggesting specific underlying pathology. In this review, I discuss linguistic aspects of PPA syndromes that may prove informative for parsing our language mechanism and identifying the neural representation of fundamental elements of language. I focus on the representation of word meaning in a discussion of semantic variant PPA, grammatical comprehension and expression in a discussion of nonfluent/agrammatic variant PPA, the supporting role of short-term memory in a discussion of logopenic variant PPA, and components of language associated with discourse in a discussion of behavioral variant frontotemporal dementia. PPA provides a novel perspective that uniquely addresses facets of language and its disorders while complementing traditional aphasia syndromes that follow stroke.

Comprehension of concrete and abstract words in semantic variant primary progressive aphasia and Alzheimer's disease: A behavioral and neuroimaging study

The aim of this study was to investigate the comprehension of concrete, abstract and abstract emotional words in semantic variant primary progressive aphasia (svPPA), Alzheimer's disease (AD), and healthy elderly adults (HE) Three groups of participants (9 svPPA, 12 AD, 11 HE) underwent a general neuropsychological assessment, a similarity judgment task, and structural brain MRI. The three types of words were processed similarly in the group of AD participants. In contrast, patients in the svPPA group were significantly more impaired at processing concrete words than abstract words, while comprehension of abstract emotional words was in between. VBM analyses showed that comprehension of concrete words relative to abstract words was significantly correlated with atrophy in the left anterior temporal lobe. These results support the view that concrete words are disproportionately impaired in svPPA, and that concrete and abstract words may rely upon partly dissociable brain regions.

The meaning of 'life' and other abstract words: Insights from neuropsychology

There are a number of long-standing theories on how the cognitive processing of abstract words, like 'life', differs from that of concrete words, like 'knife'. This review considers current perspectives on this debate, focusing particularly on insights obtained from patients with language disorders and integrating these with evidence from functional neuroimaging studies. The evidence supports three distinct and mutually compatible hypotheses. (1) Concrete and abstract words differ in their representational substrates, with concrete words depending particularly on sensory experiences and abstract words on linguistic, emotional, and magnitude-based information. Differential dependence on visual versus verbal experience is supported by the evidence for graded specialization in the anterior temporal lobes for concrete versus abstract words. In addition, concrete words have richer representations, in line with better processing of these words in most aphasic patients and, in particular, patients with semantic dementia. (2) Abstract words place greater demands on executive regulation processes because they have variable meanings that change with context. This theory explains abstract word impairments in patients with semantic-executive deficits and is supported by neuroimaging studies showing greater response to abstract words in inferior prefrontal cortex. (3) The relationships between concrete words are governed primarily by conceptual similarity, while those of abstract words depend on association to a greater degree. This theory, based primarily on interference and priming effects in aphasic patients, is the most recent to emerge and the least well understood. I present analyses indicating that patterns of lexical co-occurrence may be important in understanding these effects.

Dissociation of quantifiers and object nouns in speech in focal neurodegenerative disease

Quantifiers such as many and some are thought to depend in part on the conceptual representation of number knowledge, while object nouns such as cookie and boy appear to depend in part on visual feature knowledge associated with object concepts. Further, number knowledge is associated with a frontal-parietal network while object knowledge is related in part to anterior and ventral portions of the temporal lobe. We examined the cognitive and anatomic basis for the spontaneous speech production of quantifiers and object nouns in non-aphasic patients with focal neurodegenerative disease associated with corticobasal syndrome (CBS, n=33), behavioral variant frontotemporal degeneration (bvFTD, n=54), and semantic variant primary progressive aphasia (svPPA, n=19). We recorded a semi-structured speech sample elicited from patients and healthy seniors (n=27) during description of the Cookie Theft scene. We observed a dissociation: CBS and bvFTD were significantly impaired in the production of quantifiers but not object nouns, while svPPA were significantly impaired in the production of object nouns but not quantifiers. MRI analysis revealed that quantifier production deficits in CBS and bvFTD were associated with disease in a frontal-parietal network important for number knowledge, while impaired production of object nouns in all patient groups was related to disease in inferior temporal regions important for representations of visual feature knowledge of objects. These findings imply that partially dissociable representations in semantic memory may underlie different segments of the lexicon.

Regularity and beyond: Impaired production and comprehension of inflectional morphology in semantic dementia

Studies on inflectional morphology in semantic dementia (SD) have focused on the contrast between the regular and the irregular English past-tense. These studies aimed to contrast the claims of single- and dual-mechanism theories. However, both theories can account for impaired production of irregular verbs observed in SD. According to the dual-mechanism theory, this impairment is related to word-retrieval difficulties, while according to single-mechanism theory it is the consequence of semantic impairment. However, authors suggest that it is time to envision a broader role for semantic memory in the production of semantically encoded aspects of inflectional morphology. This study reports the performance of 10 French-speaking patients with SD in three tasks of inflectional morphology. Their performances were compared to those of a group of 20 age-, gender- and education-matched adults without cognitive impairment. Results show that SD patients had difficulties producing tense and person inflection in verbs and pseudo-verbs, whether regular or pseudo-regular. In a second task in which participants were directly exposed to regularity manipulations, SD patients tended to choose a more typical or predictable alternative over a correctly inflected verb. Results of the third task show that their difficulties in producing semantically encoded aspects of inflection, such as tense, are related to difficulties to understand the semantic content conveyed by inflectional morphemes. Overall, these results support the claim that semantic impairment can cause morphological deficits that do not only affect irregular verbs, but that also have impacts on the production and comprehension of semantic information conveyed by inflectional morphemes.

Cognitive and anatomic double dissociation in the representation of concrete and abstract words in semantic variant and behavioral variant frontotemporal degeneration

We examine the anatomic basis for abstract and concrete lexical representations in semantic memory by assessing patients with focal neurodegenerative disease. Prior evidence from healthy adult studies suggests that there may be an anatomical dissociation between abstract and concrete representations: abstract words more strongly activate the left inferior frontal gyrus relative to concrete words, while concrete words more strongly activate left anterior-inferior temporal regions. However, this double dissociation has not been directly examined. We test this dissociation in two patient groups with focal cortical atrophy in each of these regions, the behavioral variant of Frontotemporal Degeneration (bvFTD) and the semantic variant of Primary Progressive Aphasia (svPPA). We administered an associativity judgment task for abstract and concrete words, where subjects select which of two words is best associated with a given target word. Both bvFTD and svPPA patients were significantly impaired in their overall performance compared to controls. While controls treated concrete and abstract words equally, we found a category-specific double dissociation in patients' judgments: bvFTD patients showed a concreteness effect (CE), with significantly worse performance for abstract compared to concrete words, while svPPA patients showed reversal of the CE, with significantly worse performance for concrete over abstract words. Regression analyses also revealed an anatomic double dissociation: The CE is associated with inferior frontal atrophy in bvFTD, while reversal of the CE is associated with left anterior-inferior temporal atrophy in svPPA. These results support a cognitive and anatomic model of semantic memory organization where abstract and concrete representations are supported by dissociable neuroanatomic substrates.

Production of morphologically derived words in the semantic variant of primary progressive aphasia: preserved decomposition and composition but impaired validation

Although there is growing interest in inflectional morphology in semantic variant primary progressive aphasia (svPPA), derivational morphology has rarely been studied in this population. This study reports the performance of N.G., a 72-year-old-woman with svPPA in a verb production task designed to entail morphological processing (composition, decomposition) and self-appraisal of her productions. N.G. demonstrated an over-reliance on morphological processing and failures in her appraisal of root/affix combinations that resulted in the production of morphological paraphasias and neologisms. Her performance in lexical decision of verbs and pseudo-verbs points to the involvement of semantic impairment in these difficulties.

Converging evidence from fMRI and aphasia that the left temporoparietal cortex has an essential role in representing abstract semantic knowledge

While the neural underpinnings of concrete semantic knowledge have been studied extensively, abstract conceptual knowledge remains enigmatic. We present two experiments that provide converging evidence for the involvement of key regions in the temporoparietal cortex (TPC) in abstract semantic representations. First, we carried out a neuroimaging study in which participants thought deeply about abstract and concrete words. A functional connectivity analysis revealed a cortical network, including portions of the TPC, that showed coordinated activity specific to abstract word processing. In a second experiment, we tested participants with lesions involving the left TPC on a spoken-to-written word matching task using abstract and concrete target words presented in arrays of related or unrelated distractors. The results revealed an interaction between concreteness and relatedness: participants with TPC lesions were significantly less accurate for abstract words presented in related arrays than in unrelated arrays, but exhibited no effect of relatedness for concrete words. These results confirm that the TPC plays an important role in abstract concept representation and that it is part of a larger network of functionally cooperative regions needed for abstract word processing.

For richer or poorer? Imageability effects in semantic dementia patients' reading aloud

The degree to which a word's meaning evokes a mental image exerts an influence on performance across a variety of conceptual and linguistic tasks. In normal healthy participants, this effect takes the form of an advantage for high over low imageability words. Consideration of the influence of imageability on performance of patients with semantic dementia can provide information concerning its cognitive and neural bases. Semantic dementia patients show deficits in conceptual processing tasks, and an associated enhancement of the advantage for high over low imageability words. Semantic dementia patients also show deficits in linguistic processing tasks, including reading aloud words with inconsistent spelling-sound correspondences. This study provides the first systematic exploration of the influence of imageability on semantic dementia patients' reading aloud performance. Over 10 cases, the imageability effect seen for inconsistent words was actually reversed in reaction times, with faster performance for low than high imageability items. The same reversal was observed for inconsistent words when the frequency of legitimate alternative reading of components errors was considered, and this reversed effect grew larger with increasing semantic impairment. This result is interpreted in terms of the development of stronger connections along the direct pathway between spelling and sound for low than high imageability items that are then revealed under diminished semantic activation. This interpretation emphasises the interaction between form and meaning that occurs throughout learning in connectionist models.

Differing contributions of inferior prefrontal and anterior temporal cortex to concrete and abstract conceptual knowledge

Semantic cognition is underpinned by regions involved in representing conceptual knowledge and executive control areas that provide regulation of this information according to current task requirements. Using distortion-corrected fMRI, we investigated the contributions of these two systems to abstract and concrete word comprehension. We contrasted semantic decisions made either with coherent contextual support, which encouraged retrieval of a rich conceptual representation, or with irrelevant contextual information, which instead maximised demands on control processes. Inferior prefrontal cortex was activated more when decisions were made in the presence of irrelevant context, suggesting that this region is crucial for the semantic control functions required to select appropriate aspects of meaning in the face of competing information. It also exhibited greater activation for abstract words, which reflects the fact that abstract words tend to have variable, context-dependent meanings that place higher demands on control processes. In contrast, anterior temporal regions (ATL) were most active when decisions were made with the benefit of a coherent context, suggesting a representational role. There was a graded shift in concreteness effects in this region, with dorsolateral areas particularly active for abstract words and ventromedial areas preferentially activated by concrete words. This supports the idea that concrete concepts are closely associated with visual experience and abstract concepts with auditory-verbal information; and that sub-regions of the ATL display graded specialisation for these two types of knowledge. Between these two extremes, we identified significant activations for both word types in ventrolateral ATL. This area is known to be involved in representing knowledge for concrete concepts; here we established that it is also activated by abstract concepts. These results converge with data from rTMS and neuropsychological investigations in demonstrating that representational content and task demands influence recruitment of different areas in the semantic network.

The neural correlates of abstract and concrete words: evidence from brain-damaged patients

Neuropsychological and activation studies on the neural correlates of abstract and concrete words have produced contrasting results. The present study explores the anatomical substrates of abstract/concrete words in 22 brain-damaged patients with a single vascular lesion either in the right or left hemisphere. One hundred and twenty (60 concrete and 60 abstract) noun triplets were used for a semantic similarity judgment task. We found a significant interaction in word type × group since left temporal brain-damaged patients performed significantly better with concrete than abstract words. Lesion mapping of patients with predominant temporal damage showed that the left superior and middle temporal gyri and the insula were the areas of major overlapping, while the anterior portion of the left temporal lobe was generally spared. Errors on abstract words mainly concerned (although at a non-significant level) semantically associate targets, while in the case of concrete words, coordinate targets were significantly more impaired than associate ones. Our results suggest that the left superior and middle temporal gyri and the insula are crucial regions in processing abstract words. They also confirm the hypothesis of a semantic similarity vs. associative organization of concrete and abstract concepts.

Comparative semantic profiles in semantic dementia and Alzheimer's disease

Patients with the semantic variant of primary progressive aphasia, also known as semantic dementia, and Alzheimer's disease have deficits in semantic memory. However, few comparative studies have been performed to determine whether these patient groups have distinct semantic memory impairments. We asked 15 patients with semantic variant primary progressive aphasia and 57 patients with Alzheimer's disease to judge semantic category membership of coloured photos and printed words that are members of familiar natural and manufactured categories, and we related performance to grey matter atrophy. We found that both semantic variant primary progressive aphasia and Alzheimer's disease are significantly impaired on this task. Moreover, patients with semantic variant primary progressive aphasia had a significantly more prominent deficit for natural objects than their own deficit judging manufactured objects. Both semantic variant primary progressive aphasia and Alzheimer's disease had atrophy that included portions of the left temporal lobe. Regression analyses related performance in semantic variant primary progressive aphasia to ventral and medial portions of the left temporal lobe, while regression analyses in Alzheimer's disease related performance to these ventral and medial temporal areas as well as lateral temporal-parietal regions in the left hemisphere. We conclude that both semantic variant primary progressive aphasia and Alzheimer's disease are significantly impaired in a simple category membership judgement task and the selective impairment for natural kinds in semantic variant primary progressive aphasia is related in part to disease in visual association cortex in ventral-medial portions of the left temporal lobe. We discuss factors that may contribute to the semantic memory deficit in semantic variant primary progressive aphasia.

The contribution of language to the right-hemisphere conceptual representations: a selective survey

Although levels of verbal and pictorial performance are known to depend on the degree of left versus right atrophy in the early stages of semantic dementia, the nature of these differences remains controversial. It has been proposed that there is a unitary, bilaterally represented, abstract semantic system and that differential task performance reflects the impact of greater connectivity between the left anterior temporal lobe (ATL) and the left dominant language systems. This interpretation explains the greater involvement of the left ATL in verbally coded semantic knowledge, but not the prevalence of the right hemisphere in pictorial representations. An alternative account is provided by the sensory-motor model of conceptual knowledge, which assumes that each conceptual representation results from the convergence of different perceptual, motor, and verbally coded sources of knowledge in a given brain area. According to this model, the weight of verbal information should prevail in left ATL conceptual representations, because of the dominance of the left hemisphere for language, whereas the weight of sensory-motor sources of knowledge should be greater in the right ATL representations, because the right hemisphere plays a greater role in processing sensory-motor information. If the difference between right and left conceptual representations is quantitative and due to the different weight of sensory-motor and verbal sources of knowledge in their composition, we should observe an elementary, but selective representation of semantic-lexical knowledge in the intact right hemisphere and a mild but selective semantic-lexical impairment in right-brain-damaged patients. Results of the present survey support this hypothesis.

Is there a semantic system for abstract words?

Two views on the semantics of concrete words are that their core mental representations are feature-based or are reconstructions of sensory experience. We argue that neither of these approaches is capable of representing the semantics of abstract words, which involve the representation of possibly hypothetical physical and mental states, the binding of entities within a structure, and the possible use of embedding (or recursion) in such structures. Brain based evidence in the form of dissociations between deficits related to concrete and abstract semantics corroborates the hypothesis. Neuroimaging evidence suggests that left lateral inferior frontal cortex supports those processes responsible for the representation of abstract words.

Clinical diagnostic criteria and classification controversies in frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) can manifest as a spectrum of clinical syndromes, ranging from behavioural impairment to language or motor dysfunction. Recently, revised diagnostic criteria have been proposed for the behavioural and progressive aphasia syndromes associated with frontotemporal degeneration. The present review will summarize these diagnostic guidelines and highlight some lingering controversies in the classification of FTLD clinical syndromes. We will discuss common tools and methods used to identify the insidious changes of behavioural variant frontotemporal dementia (bvFTD), the value of new, patient-based tasks of orbitofrontal function, and the issue of a benign or 'phenocopy' variant of bvFTD. With regard to primary progressive aphasia (PPA), we will discuss the scope of the semantic disorder in semantic-variant PPA, the nature of the speech disorder in non-fluent, agrammatic PPA, and the preliminary utility of a logopenic PPA classification.

The degraded concept representation system in semantic dementia: damage to pan-modal hub, then visual spoke

The core clinical feature of semantic dementia is a progressive yet selective degradation of conceptual knowledge. Understanding the cognitive and neuroanatomical basis for this deficit is a key challenge for both clinical and basic science. Some researchers attribute the deficit to damage to pan-modal conceptual representations that are independent of any particular sensory-motor modality and are represented in the ventrolateral anterior temporal lobes. Others claim that damage to modality-specific visual feature representations in the occipitotemporal 'ventral stream' is responsible. In the present study, we tested the hypothesis that concept degradation in semantic dementia involves a combination of these pan-modal and modality-specific elements. We investigated factors influencing knowledge of object concepts by analysing 43 sets of picture-naming data from patients with semantic dementia. We found a strong influence of two pan-modal factors: highly familiar and typical items were named more accurately than less familiar/atypical items at all stages of the disorder. Items associated with rich sensory-motor information were also named more successfully at all stages, and this effect was present for sound/motion knowledge and tactile/action knowledge when these modalities were studied separately. However, there was no advantage for items rich in visual colour/form characteristics; instead, this factor had an increasingly negative impact in the later stages of the disorder. We propose that these results are best explained by a combination of (i) degradation of modality-independent conceptual representations, which is present throughout the disorder and is a consequence of atrophy focused on the ventrolateral anterior temporal lobes; and (ii) a later additional deficit for concepts that depend heavily on visual colour/form information, caused by the spreading of atrophy to posterior ventral temporal regions specialized for representing this information. This explanation is consistent with a graded hub-and-spoke model of conceptual knowledge, in which there is a gradual convergence of information along the temporal lobes, with visual attributes represented in the posterior cortex giving way to pan-modal representations in the anterior areas.

Strength of perceptual experience predicts word processing performance better than concreteness or imageability

Abstract concepts are traditionally thought to differ from concrete concepts by their lack of perceptual information, which causes them to be processed more slowly and less accurately than perceptually-based concrete concepts. In two studies, we examined this assumption by comparing concreteness and imageability ratings to a set of perceptual strength norms in five separate modalities: sound, taste, touch, smell and vision. Results showed that concreteness and imageability do not reflect the perceptual basis of concepts: concreteness ratings appear to be based on two different intersecting decision criteria, while imageability ratings are visually biased. Analysis of lexical decision and word naming performance showed that maximum perceptual strength (i.e., strength in the dominant perceptual modality) consistently outperformed both concreteness and imageability ratings in accounting for variance in response latency and accuracy. We conclude that so-called concreteness effects in word processing emerge from the perceptual strength of a concept's representation and discuss the implications for theories of conceptual representation.

Comprehension of concrete and abstract words in patients with selective anterior temporal lobe resection and in patients with selective amygdalo-hippocampectomy

The role of the anterior temporal lobe (ATL) in semantic memory is now firmly established. There is still controversy, however, regarding the specific role of this region in processing various types of concepts. There have been reports of patients suffering from semantic dementia (SD), a neurodegenerative condition in which the ATL is damaged bilaterally, who present with greater semantic impairment for concrete concepts than for abstract concepts, an effect known as reversal of the concreteness effect. This effect has previously been interpreted as reflecting degraded visual-perceptual features of objects due to damage to the inferior temporal lobes such as is observed in SD. Temporal lobe atrophy in SD, however, is bilateral even if it usually predominates to the left ATL, and it has been found to extend beyond the ATL, throughout the temporal lobes including medial and posterior temporal lobe regions. The question therefore remains whether greater impairment for concrete concepts results from damage to the ATL or from damage to the visual association cortex, and if unilateral damage can produce such a deficit. The aim of the present study was to investigate the processing of concrete and abstract words in rare patients who underwent a selective ATL surgical resection, and to compare their performance with that of patients with selective medial temporal lobe damage sparing the ATL region. Seven patients with a selective unilateral anterior temporal resection (ATL), 15 patients with a selective unilateral amygdalo-hippocampectomy (SeAH), and 15 healthy age- and education-matched controls underwent detailed neuropsychological assessment and carried out a semantic similarity judgment task evaluating their comprehension of concrete and abstract words. Results showed that both ATL and SeAH groups were significantly impaired on the semantic task relative to the control group. Within the patient groups, however, comprehension of concrete words was significantly more impaired than that of abstract words in the ATL group, while comprehension of abstract and concrete words was equally affected in the SeAH group. Results of this study suggest that the ATL region may play a critical role in processing concrete concepts, and that the reversal of the concreteness effect observed in ATL patients may result from damage to a categorical organization underlying the representation of concrete concepts.

When do you grasp the idea? MEG evidence for instantaneous idiom understanding

We investigated the time-course of cortical activation during comprehension of literal and idiomatic sentences using MEG and anatomically guided distributed source analysis. Previous fMRI work had shown that the comprehension of sentences including action-related words elicits somatotopic semantic activation along the motor strip, reflecting meaning aspects of constituent words. Furthermore, idioms more strongly activated temporal pole and prefrontal cortex than literal sentences. Here we show that, compared to literal sentences, processing of idioms in a silent reading task modulates anterior fronto-temporal activity very early-on, already 150-250 ms after the sentences' critical disambiguating words ("kick the habit"). In parallel, the meaning of action words embedded in sentences is reflected by somatotopic activation of precentral motor systems. As neural reflections of constituent parts of idiomatic sentences are manifest at the same early latencies as brain indexes of idiomatic vs. literal meaning processing, we suggest that within ¼ of a second, compositional and abstract context-driven semantic processes in parallel contribute to the understanding of idiom meaning.

Reverse concreteness effects are not a typical feature of semantic dementia: evidence for the hub-and-spoke model of conceptual representation

The role of anterior temporal lobes (ATLs) in semantic processing is controversial. One theory, influenced by semantic dementia (SD) patients, is that this region is a pan-modal hub for all concepts. An alternative view is that atrophy in SD specifically affects knowledge for visual features. This is supported by reports of reverse concreteness effects in a few SD patients, suggesting that abstract word knowledge is spared relative to concrete words. However, it is not clear whether such effects are typical in SD, hence reliably associated with ATL damage, because most reports are of single cases and group studies have produced conflicting results. To address these contradictions, we investigated concreteness effects in 7 SD patients, using multiple tests from earlier studies in addition to new assessments. Comprehension was impaired for both word types but was better for concrete words. However, this pattern was not found uniformly across all tests and was most likely to be observed when: 1) concrete and abstract words were well matched for word frequency and 2) concrete and abstract words were selected with sufficient variation along the imageability scale. These factors account for the variability in previous studies and indicate that reverse concreteness effects are not common in SD.

Semantic diversity accounts for the "missing" word frequency effect in stroke aphasia: insights using a novel method to quantify contextual variability in meaning

Word frequency is a powerful predictor of language processing efficiency in healthy individuals and in computational models. Puzzlingly, frequency effects are often absent in stroke aphasia, challenging the assumption that word frequency influences the behavior of any computational system. To address this conundrum, we investigated divergent effects of frequency in two comprehension-impaired patient groups. Patients with semantic dementia have degraded conceptual knowledge as a consequence of anterior temporal lobe atrophy and show strong frequency effects. Patients with multimodal semantic impairments following stroke (semantic aphasia [SA]), in contrast, show little or no frequency effect. Their deficits arise from impaired control processes that bias activation toward task-relevant aspects of knowledge. We hypothesized that high-frequency words exert greater demands on cognitive control because they are more semantically diverse--they tend to appear in a broader range of linguistic contexts and have more variable meanings. Using latent semantic analysis, we developed a new measure of semantic diversity that reflected the variability of a word's meaning across different context. Frequency, but not diversity, was a significant predictor of comprehension in semantic dementia, whereas diversity was the best predictor of performance in SA. Most importantly, SA patients did show typical frequency effects but only when the influence of diversity was taken into account. These results are consistent with the view that higher-frequency words place higher demands on control processes, so that when control processes are damaged the intrinsic processing advantages associated with higher-frequency words are masked.

How to make a spaghetti sauce with a dozen small things I cannot name: a review of the impact of semantic-memory deficits on everyday actions

The purpose of this article is to present current evidence regarding the role of semantic memory in everyday actions. First we describe key models of everyday actions. We then discuss current evidence regarding the role of semantic memory in everyday actions. We reviewed articles reporting on the execution and representation of everyday actions in populations with semantic-memory deficits and single-object use in patients with semantic dementia. Although the evidence is sparse, the general conclusion of this review is that semantic memory seems necessary to support everyday actions. Finally, future challenges and research perspectives are discussed.