Effects of tDCS on Sound Duration in Patients with Apraxia of Speech in Primary Progressive Aphasia

Abstract

Transcranial direct current stimulation (tDCS) over the left inferior frontal gyrus (IFG) was found to improve oral and written naming in post-stroke and primary progressive aphasia (PPA), speech fluency in stuttering, a developmental speech-motor disorder, and apraxia of speech (AOS) symptoms in post-stroke aphasia. This paper addressed the question of whether tDCS over the left IFG coupled with speech therapy may improve sound duration in patients with apraxia of speech (AOS) symptoms in non-fluent PPA (nfvPPA/AOS) more than sham. Eight patients with non-fluent PPA/AOS received either active or sham tDCS, along with speech therapy for 15 sessions. Speech therapy involved repeating words of increasing syllable-length. Evaluations took place before, immediately after, and two months post-intervention. Words were segmented into vowels and consonants and the duration of each vowel and consonant was measured. Segmental duration was significantly shorter after tDCS compared to sham and tDCS gains generalized to untrained words. The effects of tDCS sustained over two months post-treatment in trained and untrained sounds. Taken together, these results demonstrate that tDCS over the left IFG may facilitate speech production by reducing segmental duration. The results provide preliminary evidence that tDCS may maximize efficacy of speech therapy in patients with nfvPPA/AOS.

A Systematic Review of Transcranial Direct Current Stimulation in Primary Progressive Aphasia: Methodological Considerations

“…Studies included either a between-subject sham-controlled condition (Cotelli et al, 2014;Ficek et al, 2019a;Harris et al, 2019;de Aguiar et al, 2020a;Themistocleous et al, 2021) or a within-subject sham-controlled condition (Wang et al, 2013;Tsapkini et al, 2014Tsapkini et al, , 2018Teichmann et al, 2016;McConathey et al, 2017;Roncero et al, 2017Roncero et al, , 2019Fenner et al, 2019) 2021), who did not include a sham-controlled condition. Two studies were case studies (Wang et al, 2013;de Aguiar et al, 2021).…”

“…5 studies did not mention the spoken language of the patients (Cotelli et al, 2014(Cotelli et al, , 2016Roncero et al, 2017;de Aguiar et al, 2020ade Aguiar et al, , 2021 (in these cases, the location where the study was conducted is mentioned in the table). 1 study was performed on a Chinese-speaking patient (Wang et al, 2013), 1 study on native French speakers (Teichmann et al, 2016), and 9 studies included native English speakers (Tsapkini et al, 2014(Tsapkini et al, , 2018Gervits et al, 2016;Hung et al, 2017;McConathey et al, 2017;Fenner et al, 2019;Ficek et al, 2019a;Harris et al, 2019;Themistocleous et al, 2021). Roncero et al (2019) included fluent French or English speakers (not specifically mentioned whether it was their native language).…”

“…When provided (Cotelli et al, 2014(Cotelli et al, , 2016Tsapkini et al, 2014Tsapkini et al, , 2018Hung et al, 2017;Roncero et al, 2017Roncero et al, , 2019Fenner et al, 2019;Ficek et al, 2019a;Harris et al, 2019;de Aguiar et al, 2020ade Aguiar et al, , 2021Themistocleous et al, 2021) language therapy frequency was identical to tDCS stimulation frequency and lasted for 30-45 min or longer when needed, depending on the capabilities of the individuals. Most studies performed 5 consecutive sessions of tDCS per week, with a total of 10 ( Wang et al, 2013;Cotelli et al, 2014Cotelli et al, , 2016Gervits et al, 2016;Hung et al, 2017;McConathey et al, 2017;de Aguiar et al, 2020a) sessions per stimulation condition over 2 weeks, or 15 (Tsapkini et al, 2014(Tsapkini et al, , 2018Fenner et al, 2019;Ficek et al, 2019a;Harris et al, 2019;de Aguiar et al, 2020a;Themistocleous et al, 2021) sessions per stimulation condition over 3 weeks. Roncero et al (2017Roncero et al ( , 2019 performed 3 sessions of tDCS per week, with a total of 10 sessions per stimulation condition over 3 weeks.…”

“…Considering the argumentation of electrode placement, 13 of the 17 studies (Cotelli et al, 2014(Cotelli et al, , 2016Tsapkini et al, 2014Tsapkini et al, , 2018Hung et al, 2017;Roncero et al, 2017Roncero et al, , 2019Fenner et al, 2019;Ficek et al, 2019a;Harris et al, 2019;de Aguiar et al, 2020ade Aguiar et al, , 2021Themistocleous et al, 2021) chose their stimulation sites and concordant language therapy based on the predetermined language outcomes under evaluation to enhance task-specific improvements. Teichmann et al (2016) aspired to compare different electrode montages, specifically for patients with SvPPA, focusing on the main locus of atrophy in these patients.…”

“…Overall, tDCS combined with speech therapy resulted in significantly shorter sound durations compared to sham stimulation and compared to baseline performance, lasting until 2 months after treatment. Generalization to untrained items was significant immediately after treatment (Themistocleous et al, 2021). Cotelli et al (2014Cotelli et al ( , 2016 and Roncero et al (2017Roncero et al ( , 2019) conducted an oral picture-naming therapy for anomia.…”