This research is studying the use of low-intensity focused ultrasound (LIFU; a mild, noninvasive acoustic stimulation technique) in a small number of people to learn about its safety as a treatment for stuttering. LIFU is a small, safe sound signal that produces a gentle, pulsing flow of acoustic waves to help different parts of the brain communicate with each other. Researchers want to understand how the mild, non-invasive brain stimulation affects speech relevant brain areas, which may in turn affect speech fluency and speaking-related brain activity in people who stutter.

This study will investigate whether Low-Intensity Focused Ultrasound (LIFU; also known as transcranial ultrasound stimulation, TUS) targeting the ventral intermediate (VIM) nucleus of the thalamus can safely and feasibly modulate neural activity and improve speech fluency in adults with Persistent Developmental Stuttering (PDS).

Adult participants with PDS will be recruited through community advertisements and from existing institutional research registries, including individuals who have previously participated in noninvasive neuromodulation studies and have consented to be re-contacted for future research. All participants will complete an informed consent process prior to any study procedures.

This is a within-subject, sham-controlled study in which participants will attend multiple study visits. Study procedures include: (1) baseline behavioral and speech assessments; (2) magnetic resonance imaging (MRI), including structural imaging and diffusion tractography, to localize individualized stimulation targets; (3) functional MRI (fMRI) to assess brain connectivity; (4) neuronavigation-guided LIFU stimulation targeting the VIM thalamic nucleus; and (5) concurrent and pre/post behavioral tasks assessing speech production, reading, and rhythm perception. Participants will receive both active and sham LIFU stimulation in separate sessions.

Aim 1 is to evaluate the precision and feasibility of individualized, MRI-guided LIFU targeting of the VIM using neuronavigation and acoustic modeling. Outcomes will include alignment between intended and estimated stimulation targets and associated changes in behavioral performance and speech fluency.

Aim 2 is to identify neural biomarkers associated with response to LIFU using fMRI. Analyses will examine whether baseline thalamocortical connectivity predicts changes in functional connectivity and behavioral outcomes following stimulation.

The study is noninvasive and does not involve surgical procedures or implantation. Data collected will include neuroimaging, behavioral performance, and speech recordings. The results of this study will inform the feasibility and potential efficacy of noninvasive subcortical neuromodulation for PDS.

Inclusion Criteria:

• have normal language, hearing and cognition
• speak English as their primary language
• currently stutter
• score at least 10 (very mild) on the Stuttering Severity Instrument (SSI-4) or exhibit greater than 3% stuttered syllables during at least one of the first 3 speech samples
• have not receive any treatment for stuttering within the past year

Exclusion Criteria:

• History of seizures
• Major medical or neurological illness (e.g., stroke, serious head trauma, brain infection, Parkinson's disease, etc.)
• History of closed head injury with loss of consciousness (e.g., concussion)
• Metal or electronic implants such as cochlear implants and pacemakers
• Braids or other hair styling that prevents direct access to the scalp (if removal not possible)
• Current or planned pregnancy

Note: participants who cannot undergo MRI may complete the other portions of the study.

The Speech-Language Pathologist (SLP) conducting and scoring the speech samples to determine stuttering severity will be blind to the condition. A second SLP will score a subset of the speech samples to document reliability.

The BrainSonix BXPulser 10002 brain stimulation system does not contain a blinded mode for double blinding. The researchers will be targeting anterior nucleus of thalamus (ANT) as the sham control with previous literature utilizing ANT-LIFU as a non-motor thalamus modulation. A study team member not directly involved in any participant interaction or data analysis will randomize sessions and assign sham vs active sessions accordingly.