The goal of this study is to find out whether a type of noninvasive brain stimulation can help reduce speech errors, such as repetitions, blocks, and prolongations, in people who stutter. This pilot study will help researchers design future treatments to see if targeting certain brain areas can improve speech fluency. The study will look at how people speak and behave during both speaking and non-speaking tasks before and after the brain stimulation.

Participants will complete an online survey about 24 hours before coming to the clinic. The clinic visit will last about 3 hours and will include three phases. All parts of the study will be audio-recorded.

1. Pre-Testing: Participants will first complete a stuttering evaluation to determine whether they are typical speakers or have a mild, moderate, or severe stutter. Then, they will do several speaking and non-speaking tasks.
2. Brain Stimulation: Participants will receive a session of targeted noninvasive brain stimulation (HD-tDCS).
3. Post-Testing: After the brain stimulation, participants will repeat the same evaluation and tasks they completed during pre-testing.

Brain stimulation description:

HD-tDCS is a non-invasive technique that requires the placement of several sensors (metal electrodes) on a special cap and saline gel on your head. Very low levels of constant electrical current are delivered to specifically targeted areas of the brain via these electrodes. You may experience a slight feeling of dizziness when starting the stimulation. This occurs in a small number of subjects. This takes only a few seconds and does not affect balance after the stimulation has been completed. Several research centers have previously investigated the use of this device on healthy subjects and have found the device to be safe with no direct effect on the person's well-being. Following stimulation, participants will have the opportunity to rinse out residual gel from hair and scalp.

Inclusion Criteria:

• Must be 22 years old or older
• May be bi/multilingual but must speak English as dominant language.
• Must be diagnosed or suspected of developmental stuttering disorder. Participants will be administered the Stuttering Severity Instrument 4 and categorized as typical speakers or mild, moderate, or severe stutterers.
• Must be able to attend the session at the physical location within the clinic

Exclusion Criteria:

• Patients with preexisting speech/language disorders or previously diagnosed neurological disorders (including but not limited to apraxia of speech, cerebral palsy, dysarthria, tourettes, or any other neurological/motor condition) that affect speech/language (except stuttering) are excluded to minimize the interference of atypical brain activity.
• Participants who have acquired or neurogenic stuttering (stuttering resulting from a brain injury) are excluded, as this study focuses exclusively on the effects of developmental stuttering.
• Participants with a history of seizures
• Participants with unexplained episodes of loss of consciousness, since such condition could be related with brain alterations or epilepsy
• Participants with unstable or non controlled neuropsychiatric illness
• Participants having implanted brain medical devices
• Participants with implanted pacemakers
• Participants having any electrically,magnetically or mechanically activated implant
• Participants having cardiac, neural or medication implants
• Participants having vascular clips or any other electrically sensitive support system in the brain
• Participants with serious brain injury
• Participants showing damage of skin at sites of stimulation (the device can only be used in healthy skin without wounds, otherwise the resistance to current can be altered)
• Participants suffering from skin problems, such as dermatitis, psoriasis or eczema
• Participants suffering from severe or frequent headaches
• Participants with any serious life-threatening disease such as congestive heart failure, pulmonary obstructive chronic disease, or active neoplasia
• Pregnant women
• Participants may not consume alcohol or controlled substances within 24 hours of the scheduled appointment

Participants will complete an additional screener upon enrollment to assess medical history and current drug/medication use that may conflict with the study.

De-identified data and clinical study report will be available for the public

IPD data will be available 3 months after publication

The Clinical Study Report (CSR) will be made available upon reasonable request. Researchers must submit a brief written request describing the purpose of accessing the CSR. Requests will be reviewed by the study team for appropriateness and compliance with institutional policies.