Inflectional morphology in primary progressive aphasia: an elicited production study

Abstract

Inflectional morphology lies at the intersection of phonology, syntax and the lexicon, three language domains that are differentially impacted in the three main variants of primary progressive aphasia (PPA). To characterize spared and impaired aspects of inflectional morphology in PPA, we elicited inflectional morphemes in 48 individuals with PPA and 13 healthy age-matched controls. We varied the factors of regularity, frequency, word class, and lexicality, and used voxel-based morphometry to identify brain regions where atrophy was predictive of deficits on particular conditions. All three PPA variants showed deficits in inflectional morphology, with the specific nature of the deficits dependent on the anatomical and linguistic features of each variant. Deficits in inflecting low-frequency irregular words were associated with semantic PPA, with lexical/semantic deficits, and with left temporal atrophy. Deficits in inflecting pseudowords were associated with non-fluent/agrammatic and logopenic variants, with phonological deficits, and with left frontal and parietal atrophy.

Keywords: Inflectional morphology; Primary progressive aphasia; Semantic dementia.

Fig. 1

Accuracy in producing inflected forms as a function of word class, regularity, frequency, in the three PPA variants and age-matched controls. (A) Non-fluent/agrammatic PPA. (B) Semantic PPA. (C) Logopenic PPA. (D) Age-matched controls. Error bars show standard error of the mean.

Fig. 2

Correlations between composite measures and inflectional morphology. (A) Correlation between semantic composite score and inflection of low-frequency irregular words. (B) Correlation between phonological composite score and inflection of pseudowords.

Fig. 3

Voxel-based morphometry. Regions where parenchymal volume correlated with accuracy in inflecting low-frequency irregular words (hot) or pseudowords (blue-green) (p < 0.05, corrected for multiple comparisons).