Each participant will complete ten treatment sessions over approximately ten weeks. In each session, participants will receive active tDCS for 30 minutes while concurrently engaging in behavioral speech therapy. Active stimulation will include a 30-second ramp-up to 2.0 mA, 30 minutes of continuous stimulation, and a 30-second ramp-down.

Each participant will complete ten treatment sessions over approximately ten weeks. In each session, participants will receive sham tDCS for 30 minutes while concurrently engaging in behavioral speech therapy. Sham stimulation will involve the same ramp-up and ramp-down but with no current delivered during the 30-minute period to maintain blinding.

Stimulation (2.0 mA for 30 minutes) will occur during speech therapy sessions focused on practicing speech techniques. Sham stimulation will mimic the physical sensation without active current.

The Stuttering Severity Instrument-4th Edition (SSI-4) provides a total score that is compared to age-specific norms to determine severity, with ranges for "Very Mild" to "Very Severe". The SSI-4 calculates individual scores for frequency (2-18), duration (2-18), and physical concomitants (0-20). These individual scores are combined to create a total score, which is then ranked against norms to provide a verbal severity descriptor, such as mild, moderate, severe, or very severe.

The WASSP produces a profile of scores across five subscales. There is a total of 26 items each scored on a seven-point Likert-type scale. A score of '1' represents the least severe/negative perception, while a '7' represents the most severe/negative perception on each scale. Total scores range from 26-182, with higher scores indicating a greater negative impact of stuttering on their life.

The OASES-A is a tool used by speech-language pathologists to measure the adverse impact of stuttering on an adult's life. It consists of 100 questions rated on a 5-point scale (1-5). The scores from individual questions are added together to create an overall score. The total score is then used to determine the "Impact Rating" on a scale from mild to severe. Higher scores indicate higher levels of negative impact.

The UTBAS-6 is a six-item screening questionnaire for adults who stutter to measure unhelpful thoughts and beliefs associated with speech anxiety. The UTBAS-6 has a subscale score range of 6 to 30 and a total score range of 18 to 90. A higher score indicates more frequent unhelpful thoughts and greater anxiety related to stuttering.

Neuroplastic changes will be assessed using functional near-infrared spectroscopy (fNIRS) to measure cortical activation patterns (i.e., regional activation, functional connectivity) in/between cognitive control and speech motor areas during a delayed-naming task (pre- and post-intervention).