FV5. Tapping into neural resources of verbal communication may help overcome difficulties in speech-motor planning after stroke

Abstract

Background Decades of research highlight the importance of formulaic expressions in everyday spoken language. Utterances of this linguistic category are, by definition, fixed in form and embedded in communicative-pragmatic context (e.g., ‘Thank you,’ ‘How are you?’ or ‘I’m fine’). A growing body of neuroscience evidence suggests that formulaic expressions engage, in particular, right-hemisphere cortical and bilateral subcortical neural networks (cf. Stahl and Van Lancker Sidtis, 2015 ). This may explain why left-hemisphere stroke patients often suffer from impaired speech-motor planning, while they are still able to communicate relatively well based on a repertoire of formulaic expressions (cf. Stahl et al., 2011 ). The current study aims to provide clear behavioral evidence for the notion that using preserved formulaic language skills facilitates the spontaneous production of word onsets, one major symptom in apraxia of speech. Methods In a cross-sectional repeated-measures design, 19 individuals with chronic apraxia of speech produced German target words (e.g., /Tur/), including critical syllable onsets (e.g., /T/). Target words were preceded by a range of cues that differed, most notably, in language formulaicity (e.g., non-formulaic priming: /mu/-/Tur/, derived from /mutig/; formulaic priming: /gu/-/Tur/, derived from /guten Tag/). The experiment controlled for various influences, such as consonant–vowel structure, syllable frequency, syllable transition frequency, practice effects, meter, and articulatory tempo. Two independent phoneticians assessed the articulatory quality of the critical syllable onsets in each experimental condition (inter-rater reliability: r 0.98 ). Results Preliminary data indicate a significant articulatory benefit from formulaic language cues on critical syllable onsets, as confirmed by Wilcoxon signed-rank tests (non-formulaic versus formulaic priming: z = 3.52; p 0.001 ). Discussion The present data demonstrate an immediate effect of preserved formulaic language skills on articulatory quality in individuals with chronic apraxia of speech. As one major reason for this promising finding, we propose that patients may be capable of retrieving intact speech-motor sequences from formulaic expressions in order to re-activate the spontaneous production of word onsets. If indeed bilateral neural resources of verbal communication help reduce failures in speech-motor planning, the current results are consistent with a highly dynamic interplay of left perilesional and right intact language networks in post-stroke rehabilitation.