An Investigation of the Effect of 5 Consecutive Days of Bihemispheric TDCS on Speech Fluency in Individuals With Stuttering
Phase: NA
Conditions: Stuttering, Adult
Sponsor: Biruni University

An Invest)gat)on of the Effect of 5 Consecut)ve Days of B)hem)spher)c tDCS on Speech 
Fluency )n Ind)v)duals W)th Stutter)ng 
 
 
 
Ident'f'ers: NCT06278233 
Date: 03/01/2024 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Protocol 
In th&s study, a random&zed double-bl&nd, sham-controlled, parallel-group exper&mental research des&gn 
was appl&ed. The study &ncluded 36 adults, aged between 18 and 52 (Mdn=27.55), nat&ve Turk&sh 
speakers, r&ght-handed dom&nant, w&th developmental stutter&ng and no speech and language problems 
other than stutter&ng, who were not currently rece&v&ng therapy. Ind&v&duals under 18 years of age, w&th 
a d&agnosed bra&n les&on, w&th &ntracran&al metal &mplantat&on, w&th any neurolog&cal or psych&atr&c 
d&sorder, us&ng drugs and substances that may affect the central nervous system, and w&th a h&story of 
ep&lepsy/se&zures were excluded. Part&c&pants who voluntar&ly agreed to part&c&pate &n the study declared 
the&r w&ll&ngness to part&c&pate &n wr&t&ng by f&ll&ng out the Informed Voluntary Consent Form. The 
researcher assessed stutter&ng us&ng the Stutter&ng Sever&ty Instrument vers&on 4 (SSI-4, R&ley, 2009) 
and &mplemented the &ntervent&on. Th&s study was approved by Istanbul B&run& Un&vers&ty Non-
Intervent&onal Cl&n&cal Research Eth&cs Comm&ttee (2023/85-70). The study was reg&stered at 
Cl&n&calTr&als.gov (NCT06278233). 
 
Random-zat-on and mask-ng 
The researcher random&zed part&c&pants to the sham and tDCS study arms us&ng block random&zat&on. 
E&ght poss&ble sequences were created by select&ng block s&zes of four and s&x and these were 
random&zed. A un&que 3-d&g&t code was ass&gned per part&c&pant to conceal the allocat&on. The code was 
used to ass&gn part&c&pants to tDCS or sham st&mulat&on &n the order of the&r presentat&on 
(https://www.sealedenvelope.com/s&mple-random&ser/v1/l&sts). Bl&nd&ng was ach&eved by mask&ng the 
group ass&gnment of the assessor and part&c&pants. 
 
Procedure  
After all volunteers who wanted to part&c&pate &n the study were &nformed about the study, they f&lled 
out the Informed Voluntary Consent Form, Health Consent Form, Fl&nders Handedness Scale and 
el&g&ble part&c&pants f&lled out the OASES form. Then, the part&c&pants were ass&gned to the tDCS and 
sham study groups accord&ng to the block random&zat&on and cont&nued the&r pract&ces for f&ve 
consecut&ve days accord&ng to th&s ass&gnment. N&neteen part&c&pants rece&ved 20 m&nutes of 1-mA 
st&mulat&on for f&ve consecut&ve days, wh&le speech fluency was temporar&ly fac&l&tated us&ng 
metronome-t&med speech (one part&c&pant was only &ncluded &n the da&ly graphs and da&ly analyses 
because he attended the &ntervent&on sess&on for 4 days). The other 17 part&c&pants rece&ved the same 
speech fluency &ntervent&on w&th sham st&mulat&on. Speech fluency dur&ng read&ng and speak&ng was 
assessed at basel&ne, before and after st&mulat&on on each day of the 5-day &ntervent&on, and 1 week after 
the end of the 5-day &ntervent&on. 
 
 
F"gure 1: Exper'mental des'gn. The metr'cs used for the pr'mary outcome (% ss = percentage of stuttered syllables) and 
secondary outcomes (SSI-4, OASES) are shown 'n bold text. 

For the assessment, after collect&ng record&ngs of read&ng and speech samples, skull measurements were 
made from nas&on (Nz) to &n&on (In) and from left preacular po&nt to r&ght preacular po&nt, then a standard 
32-channel electroencephalography (EEG) co&l (EASYCAP, GmbH, Hersch&ng, Germany) was placed 
on the part&c&pants' heads to &dent&fy the st&mulat&on s&tes, and electrode placement was performed w&th 
the help of a sal&ne-soaked sponge. 
 
tDCS -ntervent-on  
In the tDCS study arm, part&c&pants rece&ved st&mulat&on at 1 mA for 20 m&nutes dur&ng the fluency 
&ntervent&on. These are frequently used tDCS parameters and were chosen because they have been 
effect&ve &n prev&ous tDCS &ntervent&on stud&es (Marangolo et al., 2013; Allman et al., 2016). The 
anode was placed on the left &nfer&or frontal cortex (at the &ntersect&on of F7 and FC5) and the cathode 
was placed at the &ntersect&on of F8 and FC6. Th&s montage has been used &n other stud&es (Yada, 
Tom7sato and Hash7moto, 2018; Karsan et al., 2022). Th&s electrode placement covers a reg&on of 
funct&onal def&c&t and wh&te matter abnormal&ty that has been &dent&f&ed &n people w&th stutter&ng 
(Watk7ns et al., 2008). The electrodes were placed &n sponges soaked &n sal&ne and placed on the scalp. 
The same electrode placement was used &n the sham st&mulat&on study arm, dur&ng wh&ch the current 
was &ncreased for 15 seconds, held at 1 mA for 15 seconds and decreased for 15 seconds at the beg&nn&ng 
of the sess&on. 
No ser&ous s&de effects were observed dur&ng the study and tDCS s&de effects were l&m&ted to the m&ld 
symptoms commonly reported &n prev&ous stud&es (e.g. &tch&ng and t&ngl&ng sensat&on under the 
electrodes). 
 
Fluency -ntervent-on (metronome-t-med speech) 
Wh&le teach&ng the part&c&pants to read w&th a metronome, the researcher f&rst presented h&s own name 
and surname as a model, and then asked the part&c&pants to say the&r names and &nterests &n accordance 
w&th the metronome tempo. Afterwards, the tDCS appl&cat&on was started and the relevant read&ng 
mater&als were shown on the computer screen used &n the study. The part&c&pants were asked to read the 
v&sual mater&als on the screen &n accordance w&th th&s metronome tempo by say&ng one syllable per 
metronome beat. When the st&mulat&on per&od ended, the tDCS was term&nated and then the post-
&mplementat&on evaluat&on phase began. In th&s phase, the part&c&pants were asked to read the read&ng 
texts normally (w&thout metronome beats) and chat about predeterm&ned top&cs. 
 
Read-ng mater-als 
Each &ntervent&on sess&on cons&sted of words and sentences pa&red &n syllable count (gradually 
&ncreas&ng &n l&ngu&st&c complex&ty from one-syllable words to f&ve-word sentences for each sess&on) 
and a wr&tten text of one of f&ve well-known stor&es (P&nocch&o, Beauty and the Beast, The Bremen 
Mus&c&ans, Rapunzel, Hansel and Gretel) w&th word counts rang&ng from 889 to 1239. 
 
Mater-als used -n evaluat-on sess-ons 
For the speak&ng assessment, two of the three pre-determ&ned conversat&on top&cs were selected based 
on the &nterests of the part&c&pants and conversat&ons were held on these two top&cs. For the read&ng 
assessment, eleven read&ng passages from the M&n&stry of Nat&onal Educat&on's 2019-2020 curr&culum 
were selected. One of these eleven passages was used &n the read&ng assessment accord&ng to the 
sequence of the pre-def&ned assessment sess&ons. Th&s ensured that each assessment sess&on was un&que 
and equally challeng&ng. 
 
Outcome measurements 
Speech fluency and read&ng fluency were measured and assessed at basel&ne, before and after the 
&ntervent&on on each &ntervent&on day, and 1 week after the &ntervent&on us&ng the percentage of syllables 
stuttered (%ss). The pr&mary outcome measure was the overall change &n fluency at the end of the 5-day 
&ntervent&on and 1 week later, but we measured how fluency was affected over the course of the 
&ntervent&on by &nclud&ng an add&t&onal assessment of change &n fluency &mmed&ately after the 
&ntervent&on sess&on on each of the 5-day &ntervent&on days. Repet&t&ons, prolongat&ons, syllable 
repet&t&ons, tense pauses and pre-speech sound block&ng were def&ned as moments of d&sfluency. For 
both read&ng and speak&ng measures, the f&rst 300 syllables were used for analys&s (syllable count ranged 

from 139-490 syllables).  An &ndependent speech-language patholog&st completed all d&sfluency counts. 
Inter-rater rel&ab&l&ty was measured by compar&ng all speech samples from 7 randomly selected 
part&c&pants w&th counts completed &ndependently by a second &ndependent speech-language patholog&st. 
 
Stat-st-cal Analys-s 
Stat&st&cal analyses were performed &n two steps. In the f&rst step, the change from the &n&t&al / basel&ne 
measurements (Day 1 pre-&ntervent&on) to the post-&ntervent&on measurements on Day 5, as well as the 
change from the &n&t&al measurements to the f&nal measurements performed on Day 12 of the tDCS and 
sham groups were compared. W&th&n the scope of the second step analyses, the change &n scores from 
the pre-&ntervent&on measurement to the post-&ntervent&on measurement was calculated for each 
treatment day (Days 1-5) and these change scores were compared between the two groups (tDCS and 
sham). S&m&lar &nferent&al stat&st&cal tests were used for the analyses descr&bed &n the f&rst and second 
steps. F&rst, for all dependent var&ables, the Shap&ro-W&lk test was used to exam&ne whether the data 
were normally d&str&buted. For the dependent var&ables that were s&gn&f&cantly d&fferent from the normal 
d&str&but&on (p < 0.05), the Mann-Wh&tney-W&lcoxon test, a nonparametr&c test, was used to compare 
whether the med&an values of &ndependent samples were d&fferent. For the dependent var&ables that were 
not s&gn&f&cantly d&fferent from the normal d&str&but&on (p > 0.05), F&sher's F-test was f&rst appl&ed to 
exam&ne whether the var&ances of the two groups (tDCS, sham) were homogeneous. If the var&ances of 
the groups were homogeneous, &ndependent samples t-test (Student's t-test), one of the parametr&c tests, 
was used to compare whether the ar&thmet&c mean values of the &ndependent samples were d&fferent. If 
the var&ances of the groups were not homogeneous, Welch's t-test was used to compare whether the 
ar&thmet&c mean values of the &ndependent samples were d&fferent. All stat&st&cal analyses were 
performed on R vers&on 4.1.2 (R Core Team, 2013).