Logopenic variant primary progressive aphasia is a neurodegenerative language disorder primarily characterized by impaired phonological processing. Sentence repetition and comprehension deficits are observed in lvPPA and linked to impaired phonological working memory, but recent evidence also implicates impaired speech perception. Currently, neural encoding of the speech envelope, which forms the scaffolding for perception, is not clearly understood in lvPPA. We leveraged recent analytical advances in electrophysiology to examine speech envelope encoding in lvPPA. We assessed cortical tracking of the speech envelope (...) and in-task comprehension of two spoken narratives in individuals with lvPPA and age-matched controls. Despite markedly reduced narrative comprehension relative to controls, individuals with lvPPA had increased cortical tracking of the speech envelope in theta oscillations, which track low-level features, but not delta oscillations, which track speech units that unfold across a longer time scale. This neural signature was highly correlated across narratives. Results indicate an increased reliance on acoustic cues during speech encoding. This may reflect inefficient encoding of bottom-up speech cues, likely as a consequence of dysfunctional temporoparietal cortex. (shrink)

Primary progressive aphasia is a clinical syndrome in which patients progressively lose speech and language abilities. Three variants are recognized: logopenic, associated with phonology and/or short-term verbal memory deficits accompanied by left temporo-parietal atrophy; semantic, associated with semantic deficits and anterior temporal lobe atrophy; non-fluent associated with grammar and/or speech-motor deficits and inferior frontal gyrus atrophy. Here, we set out to investigate whether the three variants of PPA can be dissociated based on error patterns in a single language task. We (...) recruited 21 lvPPA, 28 svPPA, and 24 nfvPPA patients, together with 31 healthy controls, and analyzed their performance on an auditory noun-to-verb generation task, which requires auditory analysis of the input, access to and selection of relevant lexical and semantic knowledge, as well as preparation and execution of speech. Task accuracy differed across the three variants and controls, with lvPPA and nfvPPA having the lowest and highest accuracy, respectively. Critically, machine learning analysis of the different error types yielded above-chance classification of patients into their corresponding group. An analysis of the error types revealed clear variant-specific effects: lvPPA patients produced the highest percentage of “not-a-verb” responses and the highest number of semantically related nouns ; in contrast, svPPA patients produced the highest percentage of “unrelated verb” responses and the highest number of light verbs. Taken together, our findings indicate that error patterns in an auditory verb generation task are associated with the breakdown of different neurocognitive mechanisms across PPA variants. Specifically, they corroborate the link between temporo-parietal regions with lexical processing, as well as ATL with semantic processes. These findings illustrate how the analysis of pattern of responses can help PPA phenotyping and heighten diagnostic sensitivity, while providing insights on the neural correlates of different components of language. (shrink)