An interventional study of Transcranial direct current stimulation in Stuttering, Adult, sponsored by Biruni University. Completed at 1 site in Turkey (Türkiye). Open to participants aged 18 Years to 60 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-03-20.
Sponsored by Biruni University · Not applicable, Interventional, and Treatment
It will be determined whether bihemispheric stimulation (anodal to the left IFG and cathodal to the right IFG) is used with fluency-facilitating conditions for 5 consecutive days in individuals with stuttering and whether there is a difference in terms of the effects seen in speech fluency compared to the sham condition.
Developmental stuttering is a fluency disorder that can negatively affect many aspects of an individual's life. Recent transcranial direct current stimulation (tDCS) studies with individuals with stuttering show that tDCS shows promise in increasing fluency when used in combination with situations that temporarily increase fluency. In this study, it was aimed to investigate the effect of bi-hemispheric tDCS on fluency in individuals with stuttering for 5 consecutive days. The hypothesis of the study is that bi-hemispheric stimulation, which includes anodal stimulation to the left hemisphere and cathodal stimulation to the right hemisphere, will be effective on reading and speech fluency when performed for 5 consecutive days. Thirty-six adults with developmental stuttering are expected to complete this double-blind, sham-controlled study. Participants will be divided into two groups by blocked randomization and one group will receive sham stimulation for 5 consecutive days and the other group will receive bihemispheric stimulation. Participants in the tDCS group will receive 20 minutes of tDCS stimulation accompanied by metronome-timed speech during the practice sessions. Reading and speaking fluency will be assessed immediately before, immediately after, and one week after the stimulation sessions. Data will be collected using the stuttering severity assessment instrument (SSI-4) Results will be compared both within and between groups in terms of percentage of stuttered syllables, stuttering severity, and evaluation of the speaker's experience of stuttering.
74 studies on the registry are indexed under Stuttering; 23 are open to participants now.
This study's enrollment of 36 is below the median of 44 across 57 interventional studies indexed under Stuttering.
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For bi-hemispheric stimulation, the anode will be placed at the intersection of F7 and FC5 and the cathode will be placed at the intersection of F8 and FC6. For all stimulations, the stimulation will be increased for 15 seconds at a dosage of 1 mA (milliampere) for the entire 20 minute session duration and decreased for 15 seconds at the end of the stimulation.
Device: Transcranial direct current stimulation
In the sham condition, the same electrode placement will be used, during which the current will be increased for 15 seconds, kept at 1 mA for 15 seconds, decreased for 15 seconds and terminated, and the 20 minute session duration will be performed with 45 seconds of real stimulation accompanied by speech with a metronome.
TDCS involves applying a weak electrical current across the head through electrodes placed on the scalp and modulating the resting membrane potential of neurons in the underlying cortex.
Stuttered Syllables in Passage Reading (Change in the Percentage of Stuttered Syllables After 5 Days of Intervention From Baseline)
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
Time frame: immediately before and immediately after the stimulation on each day of the 5-day intervention, and at 1 week after the end of the intervention.
Stuttered Syllables in Passage Reading (Change From Baseline in Percentage of Disfluent Syllables 1 Week After Intervention)
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
Time frame: immediately before and immediately after the stimulation on each day of the 5-day intervention, and at 1 week after the end of the intervention.
Stuttered Syllables in Conversation (Change in the Percentage of Stuttered Syllables After 5 Days of Intervention From Baseline)
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
Time frame: immediately before and immediately after the stimulation on each day of the 5-day intervention, and at 1 week after the end of the intervention.
Stuttered Syllables in Conversation (Change From Baseline in Percentage of Disfluent Syllables 1 Week After Intervention)
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
Time frame: immediately before and immediately after the stimulation on each day of the 5-day intervention, and at 1 week after the end of the intervention.
Change in Stuttering Severity Instrument (SSI-IV) Scores After 5 Days of Intervention From Baseline
The Stuttering Severity Instrument - Fourth Edition (SSI-4) is a standardized tool measuring stuttering severity based on three components: frequency of stuttering, duration of the three longest stuttering events, and physical concomitants. Each is converted to scaled scores-frequency and duration range from 2 to 18, and physical concomitants from 0 to 20-and summed to produce a Total Score ranging from 4 to 56, where higher scores indicate more severe stuttering. Speech naturalness is assessed separately on a 9-point scale (1 = highly natural, 9 = highly unnatural) and is not included in the Total Score. Scores are reported in scores on a scale.
Time frame: immediately before and immediately after the stimulation on each day of the 5-day intervention, and at 1 week after the end of the intervention.
Change From Baseline in Stuttering Severity Instrument (SSI-IV) Scores 1 Week After Intervention
It measures stuttering severity in the following four areas of speech behavior: (1) frequency, (2) duration, (3) physical concomitants, and (4) naturalness of the individual's speech. Frequency is expressed in percent syllables stuttered and converted to scale scores of 2-18. Duration is timed to the nearest one tenth of a second and converted to scale scores of 2-18. The four types of Physical Concomitants (Distracting Sounds, Facial Grimaces, Head Movements, and Movements of the Extremities) are converted to scale scores of 0-20. Naturalness is ranked on a scale from 1 (Highly Natural Sound Speech) to 9 (Highly Unnatural Sound Speech). Overall naturalness is ranked at the discretion of the clinician. Scaled scores of Frequency, Duration, and Physical Concomitants are added together to derive a Total Score, Percentile Rank, and Severity Equivalent.
Time frame: immediately before and immediately after the stimulation on each day of the 5-day intervention, and at 1 week after the end of the intervention.
Change in The Overall Assessment of the Speaker's Experience of Stuttering (OASES) Scores After 5 Days of Intervention From Baseline
The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.
Time frame: baseline, after the 5-day stimulation and at the 1-week post-intervention time point
Change From Baseline in The Overall Assessment of the Speaker's Experience of Stuttering (OASES) Scores 1 Week After Intervention
The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.
Time frame: baseline, after the 5-day stimulation and at the 1-week post-intervention time point
Participants were recruited between January 2024 and July 2024 at a university clinic. Recruitment was conducted through clinician referral and study advertisements placed at the clinic.
| Milestone | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Started | 19 | 17 |
| Completed | 18 | 16 |
| Not completed | 1 | 1 |
| Withdrew: Withdrawal by subject | 1 | 1 |
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
| percentage of stuttered syllables | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Stuttered Syllables in Passage Reading (Change in the Percentage of Stuttered Syllables After 5 Days of Intervention From Baseline) | -1.41 ± 8.91 | -0.81 ± 2.44 |
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
| percentage of stuttered syllables | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Stuttered Syllables in Passage Reading (Change From Baseline in Percentage of Disfluent Syllables 1 Week After Intervention) | 0.86 ± 6.59 | 0.87 ± 4.28 |
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
| percentage of stuttered syllables | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Stuttered Syllables in Conversation (Change in the Percentage of Stuttered Syllables After 5 Days of Intervention From Baseline) | -0.40 ± 3.93 | 0.07 ± 1.89 |
Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).
| percentage of stuttered syllables | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Stuttered Syllables in Conversation (Change From Baseline in Percentage of Disfluent Syllables 1 Week After Intervention) | -0.69 ± 3.59 | 0.16 ± 4.01 |
The Stuttering Severity Instrument - Fourth Edition (SSI-4) is a standardized tool measuring stuttering severity based on three components: frequency of stuttering, duration of the three longest stuttering events, and physical concomitants. Each is converted to scaled scores-frequency and duration range from 2 to 18, and physical concomitants from 0 to 20-and summed to produce a Total Score ranging from 4 to 56, where higher scores indicate more severe stuttering. Speech naturalness is assessed separately on a 9-point scale (1 = highly natural, 9 = highly unnatural) and is not included in the Total Score. Scores are reported in scores on a scale.
| score on a scale | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Change in Stuttering Severity Instrument (SSI-IV) Scores After 5 Days of Intervention From Baseline | -1.94 ± 4.82 | -1.76 ± 3.35 |
It measures stuttering severity in the following four areas of speech behavior: (1) frequency, (2) duration, (3) physical concomitants, and (4) naturalness of the individual's speech. Frequency is expressed in percent syllables stuttered and converted to scale scores of 2-18. Duration is timed to the nearest one tenth of a second and converted to scale scores of 2-18. The four types of Physical Concomitants (Distracting Sounds, Facial Grimaces, Head Movements, and Movements of the Extremities) are converted to scale scores of 0-20. Naturalness is ranked on a scale from 1 (Highly Natural Sound Speech) to 9 (Highly Unnatural Sound Speech). Overall naturalness is ranked at the discretion of the clinician. Scaled scores of Frequency, Duration, and Physical Concomitants are added together to derive a Total Score, Percentile Rank, and Severity Equivalent.
| score on a scale | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Change From Baseline in Stuttering Severity Instrument (SSI-IV) Scores 1 Week After Intervention | -3.00 ± 5.42 | -2.06 ± 3.60 |
The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.
| score on a scale | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Change in The Overall Assessment of the Speaker's Experience of Stuttering (OASES) Scores After 5 Days of Intervention From Baseline | -15.56 ± 35.72 | -8.53 ± 41.13 |
The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.
| score on a scale | Transcranial Direct Current Stimulation Study Arm | Sham Stimulation Study Arm |
|---|---|---|
| Change From Baseline in The Overall Assessment of the Speaker's Experience of Stuttering (OASES) Scores 1 Week After Intervention | -14.72 ± 25.57 | -14.19 ± 43.53 |
Collected over Adverse events were collected during the 5-day intervention and up to 1 week post-intervention.. Non-serious events are listed at a 0% frequency threshold.
| Group | Deaths | Serious | Other |
|---|---|---|---|
| Transcranial Direct Current Stimulation Study Arm | 0/19 (0%) | 0/19 (0%) | 0/19 (0%) |
| Sham Stimulation Study Arm | 0/17 (0%) | 0/17 (0%) | 0/17 (0%) |
| Age, Categorical(Participants) | tDCS | Sham | Total |
|---|---|---|---|
| <=18 years | 1 | 0 | 1 |
| Between 18 and 65 years | 18 | 17 | 35 |
| >=65 years | 0 | 0 | 0 |
| Age, Continuous(years) | tDCS | Sham | Total |
|---|---|---|---|
| Mean | 26.89 ± 6.85 | 28.29 ± 8.49 | 27.55 ± 7.59 |
| Sex: Female, Male(Participants) | tDCS | Sham | Total |
|---|---|---|---|
| Female | 4 | 1 | 5 |
| Male | 15 | 16 | 31 |
| Race and Ethnicity Not Collected(Participants) | tDCS | Sham | Total |
|---|---|---|---|
| Count of participants | — | — | 0 |
| Region of Enrollment(participants) | tDCS | Sham | Total |
|---|---|---|---|
| Turkey | 19 | 17 | 36 |
| Passage Reading (%SS)(%syllables) | tDCS | Sham | Total |
|---|---|---|---|
| Mean | 11.62 ± 8.59 | 7.34 ± 10.11 | 9.6 ± 9.46 |
| Conversation (%SS)(%syllables) | tDCS | Sham | Total |
|---|---|---|---|
| Mean | 11.49 ± 10.16 | 8.48 ± 9.80 | 10.07 ± 9.96 |
| SSI-IV total(scores on a scale) | tDCS | Sham | Total |
|---|---|---|---|
| Mean | 25.05 ± 8.66 | 20 ± 9.69 | 22.66 ± 9.38 |
8 further baseline measures are reported on the registry.
PDFs hosted by the registry, ClinicalTrials.gov.
Plan to share: Yes — Anonymized data will be made publicly available with a DOI (digital object identifier) number.
Time frame: during submission of article
Access criteria: public and no criteria
Data sharing details ↗ · osf.io
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