Impaired semantic word learning in primary progressive aphasia.

The neuropsychological and linguistic impairments in individuals with primary progressive aphasia (PPA) have been largely studied. However, the integrity of word learning ability in different PPA variants remains unexplored, despite its prominent role in language therapy. In this study, we investigated the novel word learning ability of 20 individuals with PPA (non-fluent variant: nfvPPA n = 11; logopenic variant: lvPPA n = 9) - as compared to 23 neurotypical controls (NC). Specifically, we used a contextual word learning task that required participants to discover the meaning of 48 new words across several sentences via inference from verbal contexts. We further conducted an exploratory analysis in a subsample of 8 nfvPPA, 5 lvPPA and 17 NCs using manual deterministic tractography to investigate the relationships between the language-related white matter tracts’ integrity and learning accuracy. The results revealed overall impaired word learning ability in individuals with PPA when compared to NCs and worse learning performance for individuals with lvPPA relative to nfvPPA. The tractography analyses revealed that radial diffusivity values from both dorsal and ventral language tracts were associated with learning accuracy. Our findings provide novel insights that increase our understanding of language learning impairment in individuals with PPA.