Abstract

Logopenic variant primary progressive aphasia (lvPPA) 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 (n = 10) and age-matched (n = 10) 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 (e.g., syllables), but not delta oscillations, which track speech units that unfold across a longer time scale (e.g., words, phrases, prosody). 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.

Highlights

  • Logopenic variant primary progressive aphasia is a neurodegenerative language disorder characterized by a gradual dissolution of phonological processing ability

  • The plots show that the prediction accuracies for both the narratives are highly correlated. (C) Frontocentral electrode (Fz) temporal response functions (TRF) for the theta band for each narrative

  • The gray shaded regions below each TRF mark the time regions that are significantly different between healthy controls (HC) and Logopenic variant primary progressive aphasia (lvPPA)

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Summary

INTRODUCTION

Logopenic variant primary progressive aphasia (lvPPA) is a neurodegenerative language disorder characterized by a gradual dissolution of phonological processing ability. Receptive language processing at the single-word level is relatively intact in lvPPA but deteriorates as a function of stimulus length. This pattern has been attributed to phonological working memory deficits rather than semantic or syntactic processing impairments (Lukic et al, 2019). We assess cortical tracking of the speech envelope of naturalistic, continuous speech in individuals with lvPPA (relative to age-matched controls) using EEG. This objective is motivated by converging evidence. This may manifest differently across oscillatory frequencies, so we assess the specificity

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