Grammatical impairments in PPA

Abstract

Background Grammatical impairments are commonly observed in the agrammatic subtype of primary progressive aphasia (PPA-G), whereas grammatical processing is relatively preserved in logopenic (PPA-L) and semantic (PPA-S) subtypes. Aims We review research on grammatical deficits in PPA and associated neural mechanisms, with discussion focused on production and comprehension of four aspects of morphosyntactic structure: grammatical morphology, functional categories, verbs and verb argument structure, and complex syntactic structures. We also address assessment of grammatical deficits in PPA, with emphasis on behavioral tests of grammatical processing. Finally, we address research examining the effects of treatment for progressive grammatical impairments. Main Contribution PPA-G is associated with grammatical deficits that are evident across linguistic domains in both production and comprehension. PPA-G is associated with damage to regions including the left inferior frontal gyrus (IFG) and dorsal white matter tracts, which have been linked to impaired comprehension and production of complex sentences. Detailing grammatical deficits in PPA is important for estimating the trajectory of language decline and associated neuropathology. We, therefore, highlight several new assessment tools for examining different aspects of morphosyntactic processing in PPA. Conclusions Individuals with PPA-G present with agrammatic deficit patterns distinct from those associated with PPA-L and PPA-S, but similar to those seen in agrammatism resulting from stroke, and patterns of cortical atrophy and white matter changes associated with PPA-G have been identified. Methods for clinical evaluation of agrammatism, focusing on comprehension and production of grammatical morphology, functional categories, verbs and verb argument structure, and complex syntactic structures are recommended and tools for this are emerging in the literature. Further research is needed to investigate the real-time processes underlying grammatical impairments in PPA, as well as the structural and functional neural correlates of grammatical impairments across linguistic domains. Few studies have examined the effects of treatment for grammatical impairments in PPA; research in this area is needed to better understand how (or if) grammatical processing ability can be improved, the potential for spared neural tissue to be recruited to support this, and whether the neural connections within areas of dysfunctional tissue required for grammatical processing can be enhanced using cortical stimulation.

Primary progressive aphasia and the evolving neurology of the language network

“…32–35 The patient can successfully communicate intent in short ungrammatical statements that generally contain fewer verbs than nouns. 36–40 According to our clinical observations, in mild cases of PPA-G, agrammatism might be detected only in writing samples, including emails. Most agrammatic patients also have low verbal fluency caused in part by long word-retrieval pauses that precede almost every utterance.…”

Quantitative assessment of grammar in amyloid-negative logopenic aphasia

“…These six subjects were compared to 15 Aβ-positive lvPPA and 15 agPPA participants, who were matched by age, gender, and Western Aphasia Battery Aphasia Quotient (WAB-AQ) score (Kertesz, 2007). The picture description task of the WAB was video recorded, and these speech samples were transcribed and coded for quantitative comparison between groups for syntactic structures and errors that have been shown to reveal agrammatic deficits; these included coding all grammatical categories, as well as semantic and syntactic errors, among other language variables (Ash et al, 2010; Tetzloff et al, 2018; Cynthia K Thompson & Mack, 2014). By quantifying their language production in this manner, we were able to compare the grammatical deficits of Aβ-negative lvPPA to their Aβ-positive lvPPA counterparts, as well as agPPA patients who are known to have syntactic deficits.…”

Tracking the development of agrammatic aphasia: A tensor-based morphometry study

“…Agrammatic aphasia can be observed in neurodegenerative disorders and is characterized by grammatical errors in speech or writing and impairments in comprehending syntactically complex sentences (Thompson & Mack, 2014). Early stroke studies associated the presence of agrammatic aphasia with damage to Broca’s area, located in the left inferior frontal lobe (Broca, 1865; Geschwind, 1970), although there have been disagreements in the literature concerning whether damage to Broca’s area is necessary or sufficient for the development of agrammatic aphasia (Fridriksson, Fillmore, Guo, & Rorden, 2015; Marie, 1906).…”