Semantic impairment in stroke aphasia versus semantic dementia: a case-series comparison

Semantic cognition—semantically driven verbal and nonverbal behavior—is composed of at least two interactive principal components: conceptual representations and executive control processes that regulate and shape activation within the semantic system. Previous studies indicate that semantic dementia follows from a progressive yet specific degradation of conceptual knowledge. In contrast, multimodal semantic impairment in aphasic patients (semantic aphasia [SA]) reflects damage to the control component of semantic cognition [Jefferies, E., & Lambon Ralph, M. A. Semantic impairment in stroke aphasia versus semantic dementia: A case-series comparison. Brain, 129, 2132–2147, 2006]. The purpose of the present study was to examine the nature of the semantic control deficits in SA in detail for the first time. Seven patients with SA were tested on four comprehension and naming tasks that directly manipulated the requirement for executive control in different ways. In line with many theories of cognitive control, the SA patients demonstrated three core features of impaired control: (i) they exhibited poor on-line manipulation and exploration of semantic knowledge; (ii) they exhibited poor inhibition of strongly associated distractors; and (iii) they exhibited reduced ability to focus on or augment less dominant aspects of semantic information, although the knowledge itself remained and could be successfully cued by external constraints provided by the examiner. Our findings are consistent with the notion that the anterior temporal lobes are crucial for conceptual knowledge whereas the left prefrontal and temporo-parietal cortices, damaged in patients with SA, play a critical role in regulating semantic activation in a task-appropriate fashion.

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SEMANTIC DEMENTIA WITH CATEGORY SPECIFICITY:ACOMPARATIVE CASE-SERIES STUDY

Cognitive Neuropsychology ◽

10.1080/02643290244000301 ◽

2003 ◽

Vol 20 (3-6) ◽

pp. 307-326 ◽

Cited By ~ 61

Author(s):

Matthew A. Lambon Ralph ◽

Karalyn Patterson ◽

Peter Garrard ◽

John R. Hodges

Keyword(s):

Case Series ◽

Semantic Dementia ◽

Case Series Study ◽

Series Study

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The neurophysiological architecture of semantic dementia: spectral dynamic causal modelling of a neurodegenerative proteinopathy

Scientific Reports ◽

10.1038/s41598-020-72847-1 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Elia Benhamou ◽

Charles R. Marshall ◽

Lucy L. Russell ◽

Chris J. D. Hardy ◽

Rebecca L. Bond ◽

...

Keyword(s):

Network Architecture ◽

Large Scale ◽

Effective Connectivity ◽

Brain Regions ◽

Semantic Dementia ◽

Older Individuals ◽

World Knowledge ◽

Causal Modelling ◽

Dynamic Causal Modelling ◽

Semantic Impairment

Abstract The selective destruction of large-scale brain networks by pathogenic protein spread is a ubiquitous theme in neurodegenerative disease. Characterising the circuit architecture of these diseases could illuminate both their pathophysiology and the computational architecture of the cognitive processes they target. However, this is challenging using standard neuroimaging techniques. Here we addressed this issue using a novel technique—spectral dynamic causal modelling—that estimates the effective connectivity between brain regions from resting-state fMRI data. We studied patients with semantic dementia—the paradigmatic disorder of the brain system mediating world knowledge—relative to healthy older individuals. We assessed how the effective connectivity of the semantic appraisal network targeted by this disease was modulated by pathogenic protein deposition and by two key phenotypic factors, semantic impairment and behavioural disinhibition. The presence of pathogenic protein in SD weakened the normal inhibitory self-coupling of network hubs in both antero-mesial temporal lobes, with development of an abnormal excitatory fronto-temporal projection in the left cerebral hemisphere. Semantic impairment and social disinhibition were linked to a similar but more extensive profile of abnormally attenuated inhibitory self-coupling within temporal lobe regions and excitatory projections between temporal and inferior frontal regions. Our findings demonstrate that population-level dynamic causal modelling can disclose a core pathophysiological feature of proteinopathic network architecture—attenuation of inhibitory connectivity—and the key elements of distributed neuronal processing that underwrite semantic memory.

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Semantic dementia: Brazilian study of nineteen cases

Dementia & Neuropsychologia ◽

10.1590/s1980-57642008dn10400007 ◽

2007 ◽

Vol 1 (4) ◽

pp. 366-373 ◽

Cited By ~ 3

Author(s):

Mirna Lie Hosogi Senaha ◽

Paulo Caramelli ◽

Claudia Sellitto Porto ◽

Ricardo Nitrini

Keyword(s):

Semantic Memory ◽

Temporal Lobe ◽

Clinical Characteristics ◽

Case Series ◽

Semantic Dementia ◽

Brazilian Sample ◽

Dementia Syndrome ◽

Visuospatial Skills ◽

Low Performance ◽

Lobe Atrophy

Abstract The term semantic dementia was devised by Snowden et al. in 1989 and nowadays, the semantic dementia syndrome is recognized as one of the clinical forms of frontotemporal lobar degeneration (FTLD) and is characterized by a language semantic disturbance associated to non-verbal semantic memory impairment. Objectives: The aim of this study was to describe a Brazilian sample of 19 semantic dementia cases, emphasizing the clinical characteristics important for differential diagnosis of this syndrome. Methods: Nineteen cases with semantic dementia were evaluated between 1999 and 2007. All patients were submitted to neurological evaluation, neuroimaging exams and cognitive, language and semantic memory evaluation. Results: All patients presented fluent spontaneous speech, preservation of syntactic and phonological aspects of the language, word-finding difficulty, semantic paraphasias, word comprehension impairment, low performance in visual confrontation naming tasks, impairment on tests of non-verbal semantic memory and preservation of autobiographical memory and visuospatial skills. Regarding radiological investigations, temporal lobe atrophy and/or hypoperfusion were found in all patients. Conclusions: The cognitive, linguistic and of neuroimaging data in our case series corroborate other studies showing that semantic dementia constitutes a syndrome with well defined clinical characteristics associated to temporal lobe atrophy.

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Going beyond Inferior Prefrontal Involvement in Semantic Control: Evidence for the Additional Contribution of Dorsal Angular Gyrus and Posterior Middle Temporal Cortex

Journal of Cognitive Neuroscience ◽

10.1162/jocn_a_00442 ◽

2013 ◽

Vol 25 (11) ◽

pp. 1824-1850 ◽

Cited By ~ 221

Author(s):

Krist A. Noonan ◽

Elizabeth Jefferies ◽

Maya Visser ◽

Matthew A. Lambon Ralph

Keyword(s):

Functional Neuroimaging ◽

Semantic Network ◽

Temporal Cortex ◽

Case Series ◽

Regulatory Control ◽

Angular Gyrus ◽

Additional Contribution ◽

Middle Temporal ◽

Semantic Cognition ◽

Semantic Impairment

Semantic cognition requires a combination of semantic representations and executive control processes to direct activation in a task- and time-appropriate fashion [Jefferies, E., & Lambon Ralph, M. A. Semantic impairment in stroke aphasia versus semantic dementia: A case-series comparison. Brain, 129, 2132–2147, 2006]. We undertook a formal meta-analysis to investigate which regions within the large-scale semantic network are specifically associated with the executive component of semantic cognition. Previous studies have described in detail the role of left ventral pFC in semantic regulation. We examined 53 studies that contrasted semantic tasks with high > low executive requirements to determine whether cortical regions beyond the left pFC show the same response profile to executive semantic demands. Our findings revealed that right pFC, posterior middle temporal gyrus (pMTG) and dorsal angular gyrus (bordering intraparietal sulcus) were also consistently recruited by executively demanding semantic tasks, demonstrating patterns of activation that were highly similar to the left ventral pFC. These regions overlap with the lesions in aphasic patients who exhibit multimodal semantic impairment because of impaired regulatory control (semantic aphasia)—providing important convergence between functional neuroimaging and neuropsychological studies of semantic cognition. Activation in dorsal angular gyrus and left ventral pFC was consistent across all types of executive semantic manipulation, regardless of whether the task was receptive or expressive, whereas pMTG activation was only observed for manipulation of control demands within receptive tasks. Second, we contrasted executively demanding tasks tapping semantics and phonology. Our findings revealed substantial overlap between the two sets of contrasts within left ventral pFC, suggesting this region underpins domain-general control mechanisms. In contrast, we observed relative specialization for semantic control within pMTG as well as the most ventral aspects of left pFC (BA 47), consistent with our proposal of a distributed network underpinning semantic control.

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The Word Processing Deficit in Semantic Dementia: All Categories Are Equal, but Some Categories Are More Equal than Others

Journal of Cognitive Neuroscience ◽

10.1162/jocn.2009.21339 ◽

2010 ◽

Vol 22 (9) ◽

pp. 2027-2041 ◽

Cited By ~ 60

Author(s):

Friedemann Pulvermüller ◽

Elisa Cooper-Pye ◽

Clare Dine ◽

Olaf Hauk ◽

Peter J. Nestor ◽

...

Keyword(s):

Speech Acts ◽

Conceptual Knowledge ◽

Word Processing ◽

Case Series ◽

Specific Pattern ◽

Semantic Dementia ◽

Semantic Features ◽

Topography Model ◽

Semantic Hub ◽

Action Verbs

It has been claimed that semantic dementia (SD), the temporal variant of fronto-temporal dementia, is characterized by an across-the-board deficit affecting all types of conceptual knowledge. We here confirm this generalized deficit but also report differential degrees of impairment in processing specific semantic word categories in a case series of SD patients (N = 11). Within the domain of words with strong visually grounded meaning, the patients' lexical decision accuracy was more impaired for color-related than for form-related words. Likewise, within the domain of action verbs, the patients' performance was worse for words referring to face movements and speech acts than for words semantically linked to actions performed with the hand and arm. Psycholinguistic properties were matched between the stimulus groups entering these contrasts; an explanation for the differential degrees of impairment must therefore involve semantic features of the words in the different conditions. Furthermore, this specific pattern of deficits cannot be captured by classic category distinctions such as nouns versus verbs or living versus nonliving things. Evidence from previous neuroimaging research indicates that color- and face/speech-related words, respectively, draw most heavily on anterior-temporal and inferior-frontal areas, the structures most affected in SD. Our account combines (a) the notion of an anterior-temporal amodal semantic “hub” to explain the profound across-the-board deficit in SD word processing, with (b) a semantic topography model of category-specific circuits whose cortical distributions reflect semantic features of the words and concepts represented.

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Deregulated Semantic Cognition Follows Prefrontal and Temporo-parietal Damage: Evidence from the Impact of Task Constraint on Nonverbal Object Use

Journal of Cognitive Neuroscience ◽

10.1162/jocn.2010.21539 ◽

2011 ◽

Vol 23 (5) ◽

pp. 1125-1135 ◽

Cited By ~ 52

Author(s):

Faye Corbett ◽

Elizabeth Jefferies ◽

Matthew A. Lambon Ralph

Keyword(s):

Conceptual Knowledge ◽

Case Series ◽

Semantic Knowledge ◽

Regulatory Control ◽

Task Constraint ◽

Semantic Cognition ◽

Object Use ◽

Task Conditions ◽

The Impact ◽

Semantic Impairment

Semantic cognition, which encompasses all conceptually based behavior, is dependent on the successful interaction of two key components: conceptual representations and regulatory control. Qualitatively distinct disorders of semantic knowledge follow damage to the different parts of this system. Previous studies have shown that patients with multimodal semantic impairment following CVA—a condition referred to as semantic aphasia (SA)—perform poorly on a range of conceptual tasks due to a failure of executive control following prefrontal and/or temporo-parietal infarction [Jefferies, E., & Lambon Ralph, M. A. Semantic impairment in stroke aphasia versus semantic dementia: A case-series comparison. Brain, 129, 2132–2147, 2006]. Although a deficit of core semantic control would be expected to impair all modalities in parallel, most research exploring this condition has focused on tasks in the verbal domain. In a novel exploration of semantic control in the nonverbal domain, therefore, we assessed eight patients with SA on two experiments that examined object use knowledge under different levels of task constraint. Patients exhibited three key characteristics of semantic deregulation: (a) difficulty using conceptual knowledge flexibly to support the noncanonical uses of everyday objects; (b) poor inhibition of semantically related distractor items; and (c) improved object use with the provision of more tightly constraining task conditions following verbal and pictorial cues. Our findings are consistent with the notion that a neural network incorporating the left inferior prefrontal and temporo-parietal areas (damaged in SA) underpins regulation of semantic activation across both verbal and nonverbal modalities.

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