The Brain Network of Naming: A Lesson from Primary Progressive Aphasia

Abstract

ObjectiveWord finding depends on the processing of semantic and lexical information, and it involves an intermediate level for mapping semantic-to-lexical information which also subserves lexical-to-semantic mapping during word comprehension. However, the brain regions implementing these components are still controversial and have not been clarified via a comprehensive lesion model encompassing the whole range of language-related cortices. Primary progressive aphasia (PPA), for which anomia is thought to be the most common sign, provides such a model, but the exploration of cortical areas impacting naming in its three main variants and the underlying processing mechanisms is still lacking.MethodsWe addressed this double issue, related to language structure and PPA, with thirty patients (11 semantic, 12 logopenic, 7 agrammatic variant) using a picture-naming task and voxel-based morphometry for anatomo-functional correlation. First, we analyzed correlations for each of the three variants to identify the regions impacting naming in PPA and to disentangle the core regions of word finding. We then combined the three variants and correlation analyses for naming (semantic-to-lexical mapping) and single-word comprehension (lexical-to-semantic mapping), predicting an overlap zone corresponding to a bidirectional lexical-semantic hub.Results and ConclusionsOur results showed that superior portions of the left temporal pole and left posterior temporal cortices impact semantic and lexical naming mechanisms in semantic and logopenic PPA, respectively. In agrammatic PPA naming deficits were rare, and did not correlate with any cortical region. Combined analyses revealed a cortical overlap zone in superior/middle mid-temporal cortices, distinct from the two former regions, impacting bidirectional binding of lexical and semantic information. Altogether, our findings indicate that lexical/semantic word processing depends on an anterior-posterior axis within lateral-temporal cortices, including an anatomically intermediate hub dedicated to lexical-semantic integration. Within this axis our data reveal the underpinnings of anomia in the PPA variants, which is of relevance for both diagnosis and future therapy strategies.

Regional Distribution, Asymmetry, and Clinical Correlates of Tau Uptake on [18F]AV-1451 PET in Atypical Alzheimer’s Disease

“…Tau uptake bilaterally in the frontal and temporal lobe was associated with deficits in sentence repetition, as well as in the left parietal region, likely reflecting disruption of the language network [48]. There was also a trend for tau uptake in both temporal lobes to be associated with poorer naming, concordant with the role of the temporal lobes in anomia and semantic processing [49]. Tau uptake bilaterally in the occipital lobe was related to severity of both simultanagnosia and visuoperceptual function, features which have previously been associated with dysfunction in the occipital lobe [4, 17, 43, 50–52].…”

Dyslexic Characteristics of Chinese-Speaking Semantic Variant of Primary Progressive Aphasia

“…Abel et al provided neurophysiological evidence that the left and right anterior temporal lobe showed robust beta-band during visual naming of famous people and tools {52}. In studies investigating the temporal lobe in language processing in PPA, Wilson et al demonstrated that its role in sentence processing is likely to relate to higher-level processes such as combinatorial semantic processing {53}, while Migliaccio and colleagues demonstrated its role in binding of lexical and semantic information in bidirectional manner {54}. As Chinese is a logographical language, where semantic data is tagged to each individual character, we speculate that this region also serves as a center of convergence of lexical semantics of the language, particularly in logographical languages.…”

Jargonaphasia: A Systematic Overview and Characterization in Primary Progressive Aphasia

“…Such evolutions towards distinct jargonaphasia phenotypes are in line with the distinct language deficits in the 2 PPA variants. Lv-PPA is characterized by progressive erosion of the phonological lexicon in posterior temporal regions [23,36], whereas semantic PPA leads to the breakdown of semantic representations in anterior temporal regions [23]. Lv-PPA therefore leads to structural distortions of the output lexicon with instable and blurred lexical representations, which is the causative factor of phonemic or syllabic inversions/substitutions/insertions.…”