Abstract
Delayed auditory feedback (DAF) is a classical paradigm for probing sensori-motor interactions in speech output and has been studied in various disorders associated with speech dysfluency and aphasia. However, little information is available concerning the effects of DAF on degenerating language networks in primary progressive aphasia: the paradigmatic “language-led dementias.” Here we studied two forms of speech output (reading aloud and propositional speech) under natural listening conditions (no feedback delay) and under DAF at 200 ms, in a cohort of 19 patients representing all major primary progressive aphasia syndromes vs. healthy older individuals and patients with other canonical dementia syndromes (typical Alzheimer's disease and behavioral variant frontotemporal dementia). Healthy controls and most syndromic groups showed a quantitatively or qualitatively similar profile of reduced speech output rate and increased speech error rate under DAF relative to natural auditory feedback. However, there was no group effect on propositional speech output rate under DAF in patients with nonfluent primary progressive aphasia and logopenic aphasia. Importantly, there was considerable individual variation in DAF sensitivity within syndromic groups and some patients in each group (though no healthy controls) apparently benefited from DAF, showing paradoxically increased speech output rate and/or reduced speech error rate under DAF. This work suggests that DAF may be an informative probe of pathophysiological mechanisms underpinning primary progressive aphasia: identification of “DAF responders” may open up an avenue to novel therapeutic applications.
Highlights
Speech production is a highly complex process that depends on an interaction of motor and perceptual mechanisms
Correspondences between progressive aphasias (PPA) and classical vascular aphasic syndromes are loose, svPPA can be characterized as a fluent aphasic disorder, whereas nfvPPA shares several key features with Broca’s aphasia. lvPPA has certain features of conduction aphasia but is characterized by word-retrieval deficits and considerable dysfluency in a high proportion of patients [20, 21]
We have shown that canonical PPA syndromes are associated with differential sensitivity to delayed auditory feedback (DAF) at latency 200 ms; and that sensitivity to DAF is significantly reduced in nfvPPA, as indexed by a lack of effect on propositional speech output compared with a healthy older control cohort
Summary
Speech production is a highly complex process that depends on an interaction of motor and perceptual mechanisms. Perturbing auditory feedback has been shown to affect vocal output. The effects of DAF in the canonical neurodegenerative disorders of language— the primary progressive aphasias (PPA)—have not been investigated. These neurodegenerative proteinopathies are clinically, neuroanatomically and histopathologically diverse, comprising three cardinal syndromic variants: the nonfluent variant (nfvPPA), characterized by impaired speech production and agrammatism due to predominant peri-Sylvian cortical degeneration; the semantic variant (svPPA), characterized by impaired word and object knowledge due to selective anterior temporal lobe degeneration; and the logopenic variant (lvPPA), characterized by impaired phonological transcoding attributable to predominant temporo-parietal cortical degeneration [20]. Correspondences between PPA and classical vascular aphasic syndromes are loose, svPPA can be characterized as a fluent aphasic disorder, whereas nfvPPA shares several key features with Broca’s aphasia. lvPPA has certain features of conduction aphasia but is characterized by word-retrieval deficits and considerable dysfluency in a high proportion of patients [20, 21]
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