scholarly journals Elucidating the Nature of Deregulated Semantic Cognition in Semantic Aphasia: Evidence for the Roles of Prefrontal and Temporo-parietal Cortices

2010 ◽  
Vol 22 (7) ◽  
pp. 1597-1613 ◽  
Author(s):  
Krist A. Noonan ◽  
Elizabeth Jefferies ◽  
Faye Corbett ◽  
Matthew A. Lambon Ralph
Keyword(s):  
Executive Control ◽  
Conceptual Knowledge ◽  
Critical Role ◽  
Case Series ◽  
Semantic Knowledge ◽  
Semantic Dementia ◽  
Semantic Cognition ◽  
On Line ◽  
Parietal Cortices ◽  
Semantic Impairment

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.

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

2011 ◽  
Vol 23 (5) ◽  
pp. 1125-1135 ◽  
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.

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

Brain ◽  
2006 ◽  
Vol 129 (8) ◽  
pp. 2132-2147 ◽  
Author(s):  
Elizabeth Jefferies ◽  
Matthew A. Lambon Ralph
Keyword(s):  
Case Series ◽  
Semantic Dementia ◽  
Semantic Impairment

The interplay between control processes and feature relevance: Evidence from dual-task methodology

2019 ◽  
Vol 73 (3) ◽  
pp. 384-395
Author(s):  
Maria Montefinese ◽  
Glyn Hallam ◽  
Hannah Elizabeth Thompson ◽  
Elizabeth Jefferies
Keyword(s):  
Divided Attention ◽  
Dual Task ◽  
Conceptual Knowledge ◽  
Semantic Representation ◽  
Semantic Knowledge ◽  
Semantic Retrieval ◽  
Semantic Cognition ◽  
Control Processes ◽  
And Control ◽  
Healthy Participants

Neuropsychological studies suggest a distinction between (a) semantic knowledge and (b) control processes that shape the retrieval of conceptual information to suit the task or context. These aspects of semantic cognition are specifically impaired in patients with semantic dementia and semantic aphasia, respectively. However, interactions between the structure of knowledge and control processes that are expected during semantic retrieval have not been fully characterised. In particular, domain-general executive resources may not have equal relevance for the capacity to promote weak yet task relevant features (i.e., “controlled retrieval) and to ignore or suppress distracting information (i.e., “selection”). Here, using a feature selection task, we tested the contribution of featural relevance to semantic performance in healthy participants under conditions of divided attention. Healthy participants showed greater dual-task disruption as the relevance value of the distractor feature linearly increased, supporting the emerging view that semantic relevance is one of the organising principles of the structure of semantic representation. Moreover, word frequency, and inter-correlational strength affected overall performance, but they did not show an interaction with dual-task conditions. These results suggest that domain-general control processes, disrupted by divided attention, are more important to the capacity to efficiently avoid distracting information during semantic decision-making than to the promotion of weak target features. The present study therefore provides novel information about the nature of the interaction between structured conceptual knowledge and control processes that support the retrieval of appropriate information and relates these results to a new theoretical framework, termed controlled semantic cognition.

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

2013 ◽  
Vol 25 (11) ◽  
pp. 1824-1850 ◽  
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.

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

2010 ◽  
Vol 22 (9) ◽  
pp. 2027-2041 ◽  
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.

scholarly journals An individual differences approach to semantic cognition: Divergent effects of age on representation, retrieval and selection

2017 ◽  
Author(s):  
Paul Hoffman
Keyword(s):  
Older People ◽  
Executive Control ◽  
Semantic Information ◽  
Later Life ◽  
Semantic Knowledge ◽  
Semantic Representations ◽  
Semantic Cognition ◽  
Control Processes ◽  
The Relationship ◽  
Representation Of Knowledge

AbstractSemantic cognition refers to the appropriate use of acquired knowledge about the world. This requires representation of knowledge as well as control processes which ensure that currently-relevant aspects of knowledge are retrieved and selected. Although these abilities can be impaired selectively following brain damage, the relationship between them in healthy individuals is unclear. It is also commonly assumed that semantic cognition is preserved in later life, because older people have greater reserves of knowledge. However, this claim overlooks the possibility of decline in semantic control processes. Here, semantic cognition was assessed in 100 young and older adults. Despite having a broader knowledge base, older people showed specific impairments in semantic control, performing more poorly than young people when selecting among competing semantic representations. Conversely, they showed preserved controlled retrieval of less salient information from the semantic store. Breadth of semantic knowledge was positively correlated with controlled retrieval but was unrelated to semantic selection ability, which was instead correlated with non-semantic executive function. These findings indicate that three distinct elements contribute to semantic cognition: semantic representations that accumulate throughout the lifespan, processes for controlled retrieval of less salient semantic information, which appear age-invariant, and mechanisms for selecting task-relevant aspects of semantic knowledge, which decline with age and may relate more closely to domain-general executive control.

scholarly journals The interplay between semantic control processes and feature relevance: Evidence from dual task methodology

2018 ◽  
Author(s):  
Maria Montefinese ◽  
Glyn Hallam ◽  
Hannah Thompson ◽  
Beth Jefferies
Keyword(s):  
Divided Attention ◽  
Dual Task ◽  
Conceptual Knowledge ◽  
Semantic Representation ◽  
Semantic Knowledge ◽  
Semantic Retrieval ◽  
Semantic Cognition ◽  
Control Processes ◽  
And Control ◽  
Healthy Participants

Neuropsychological studies suggest a distinction between (i) semantic knowledge and (ii) control processes that shape the retrieval of conceptual information to suit the task or context. These aspects of semantic cognition are specifically impaired in patients with semantic dementia and semantic aphasia respectively. However, interactions between the structure of knowledge and control processes that are expected during semantic retrieval have not been fully characterised. In particular, domain-general executive resources may not have equal relevance for the capacity to promote weak yet relevant features (i.e., “controlled retrieval), and to ignore or suppress distracting information (i.e., “selection”). Here, using a feature selection task, we tested the contribution of featural relevance to semantic performance in healthy participants under conditions of divided attention. Healthy participants showed greater dual-task disruption as the relevance value of the distracter feature linearly increased, supporting the emerging view that semantic relevance is one of the organizing principles of the structure of semantic representation. Moreover, target relevance, word frequency and inter-correlational strength affected overall performance, but they did not show an interaction with dual-task conditions. These results suggest that domain-general control processes, disrupted by divided attention, are more relevant to the capacity to efficiently avoid distracting information during semantic decision-making than to the promotion of weak target features. The present study therefore provides novel information about the nature of the interaction between structured conceptual knowledge and control processes that support the retrieval of appropriate information, and relates these results to a new theoretical framework, termed controlled semantic cognition.

scholarly journals “Presemantic” Cognition in Semantic Dementia: Six Deficits in Search of an Explanation

2006 ◽  
Vol 18 (2) ◽  
pp. 169-183 ◽  
Author(s):  
Karalyn Patterson ◽  
Matthew A. Lambon Ralph ◽  
Elizabeth Jefferies ◽  
Anna Woollams ◽  
Roy Jones ◽  
...  
Keyword(s):  
Factor Analysis ◽  
Lexical Decision ◽  
Reading Aloud ◽  
Semantic Knowledge ◽  
Specific Pattern ◽  
Semantic Dementia ◽  
Object Decision ◽  
Atypical Feature ◽  
Semantic Impairment

On the basis of a theory about the role of semantic knowledge in the recognition and production of familiar words and objects, we predicted that patients with semantic dementia would reveal a specific pattern of impairment on six different tasks typically considered “pre-” or “non-” semantic: reading aloud, writing to dictation, inflecting verbs, lexical decision, object decision, and delayed copy drawing. The prediction was that all tasks would reveal a frequency-by-typicality interaction, with patients performing especially poorly on lower-frequency items with atypical structure (e.g., words with an atypical spelling-to-sound relationship; objects with an atypical feature for their class, such as the hump on a camel, etc). Of 84 critical observations (14 patients performing 6 tasks), this prediction was correct in 84/84 cases; and a single component in a factor analysis accounted for 87% of the variance across seven measures: each patient's degree of impairment on atypical items in the six experimental tasks and a separate composite score reflecting his or her degree of semantic impairment. Errors also consistently conformed to the predicted pattern for both expressive and receptive tasks, with responses reflecting residual knowledge about the typical surface structure of each domain. We argue that these results cannot be explained as associated but unrelated deficits but instead are a principled consequence of a primary semantic impairment.

scholarly journals Demonstrating the Qualitative Differences between Semantic Aphasia and Semantic Dementia: A Novel Exploration of Nonverbal Semantic Processing

2013 ◽  
Vol 26 (1-2) ◽  
pp. 7-20 ◽  
Author(s):  
Krist A. Noonan ◽  
Peter Garrard ◽  
Elizabeth Jefferies ◽  
Sheeba Eshan ◽  
Matthew A. Lambon Ralph
Keyword(s):  
Semantic Processing ◽  
Semantic Category ◽  
Semantic Knowledge ◽  
Semantic Dementia ◽  
Regulatory Control ◽  
Task Structure ◽  
Fine Grained ◽  
Regulatory Processes ◽  
Patient Groups ◽  
Semantic Impairment

Semantic dementia (SD) implicates the anterior temporal lobes (ATL) as a critical substrate for semantic memory. Multi-modal semantic impairment can also be a feature of post-stroke aphasia (referred to here as “semantic aphasia” or SA) where patients show impaired regulatory control accompanied by lesions to the frontal and/or temporo-parietal cortices, and thus the two patient groups demonstrate qualitatively different patterns of semantic impairment [1]. Previous comparisons of these two patient groups have tended to focus on verbal receptive tasks. Accordingly, this study investigated nonverbal receptive abilities via a comparison of reality decision judgements in SD and SA. Pictures of objects were presented alongside non-real distracters whose features were altered to make them more/less plausible for the semantic category. The results highlighted a number of critical differences between the two groups. Compared to SD patients, SA patients: (1) were relatively unimpaired on the two alternative forced choice (2AFC) decisions despite showing a comparable degree of semantic impairment on other assessments; (2) showed minimal effects of the plausibility manipulation; (3) were strongly influenced by variations in the regulatory requirements of tasks; and (4) exhibited a reversed effect of familiarity–i.e., better performance on less commonly encountered items. These results support a distinction between semantic impairments which arise from impaired regulatory processes (e.g., SA) versus those where degraded semantic knowledge is the causal factor (e.g., SD). SA patients performed relatively well because the task structure reduced the requirement for internally generated control. In contrast, SD patients performed poorly because their degraded knowledge did not allow the fine-grained distinctions required to complete the task.

scholarly journals Unpicking the Semantic Impairment in Alzheimer’s Disease: Qualitative Changes with Disease Severity

2012 ◽  
Vol 25 (1) ◽  
pp. 23-34 ◽  
Author(s):  
Faye Corbett ◽  
Elizabeth Jefferies ◽  
Alistair Burns ◽  
Matthew A. Lambon Ralph
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Cognitive Control ◽  
Disease Severity ◽  
Conceptual Knowledge ◽  
Control Mechanisms ◽  
Semantic Representations ◽  
Dual Nature ◽  
Semantic Cognition ◽  
Semantic Impairment

Despite a vast literature examining semantic impairment in Alzheimer's disease (AD), consensus regarding the nature of the deficit remains elusive. We re-considered this issue in the context of a framework that assumes semantic cognition can break down in two ways: (1) core semantic representations can degrade or (2) cognitive control mechanisms can become impaired [1]. We hypothesised and confirmed that the nature of semantic impairment in AD changes with disease severity. Patients at mild or severe stages of the disorder exhibited impairment across various semantic tasks but the nature of those deficits differed qualitatively for the two groups. Commensurate with early dysfunction of the cognitive control, temporoparietal-frontal-cingulate network, characteristics of deregulated semantic cognition were exhibited by the mild AD cases. In contrast, the severe AD group reproduced features of additional degradation of core semantic representations. These results suggest that spread of pathology into lateral anterior temporal lobes in later stage AD produces degradation of semantic representations, exacerbating the already deregulated system. Moreover, the dual nature of severe patients’ impairment was highlighted by disproportionately poor performance on tasks placing high demand on both conceptual knowledge and control processes–e.g., category fluency.

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