Noninvasive Thalamocortical Neuromodulation With Low-Intensity Focused Ultrasound for Persistent Developmental Stuttering

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 safety, feasibility, and precision of individualized, MRI-guided LIFU targeting of the left VIM thalamus using neuronavigation and post-hoc acoustic simulation. Feasibility outcomes include targeting accuracy, protocol adherence, adverse event monitoring, and participant tolerability.

Aim 2 is to characterize the acute neural and behavioral effects of excitatory VIM-LIFU relative to an active anatomical sham condition (ANT-LIFU) using a within-subjects, double-blind crossover design. Primary outcome is the change in speech fluency (stuttered syllable percentage). Secondary outcomes are motor inhibition (stop-signal reaction time), and beat-based rhythm discrimination (d'). Exploratory neural outcomes include pre-to-post changes in resting-state thalamocortical functional connectivity and task-based (stop-signal fMRI) connectivity between VIM and speech motor regions (IFG, STN, pre-SMA). Exploratory analyses will also 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
• Any active, unstable, or inadequately treated psychiatric condition, including but not limited to psychosis, active major depressive episode, bipolar disorder with recent mood episode, or current suicidal ideation.
• Current use of antipsychotic medications for treatment of a primary psychotic disorder or bipolar disorder; current use of mood stabilizers (e.g., lithium, valproate) or benzodiazepines. Low-dose adjunctive use of atypical antipsychotics (e.g., brexpiprazole, aripiprazole, quetiapine) for treatment-resistant depression or anxiety is not exclusionary if the participant's condition is stable per the existing ≥2-month stability criterion.
• Any condition or medication that lowers seizure threshold, consistent with standard practice across non-invasive brain stimulation protocols.

Note: participants who cannot undergo MRI may complete the other portions of the study. For participants who cannot undergo MRI can be targeted for LIFU stimulation using a standard T1 scan. Resting state fMRI measures taken before and after stimulation will also be omitted for these cases. But the behavioral and speech measures can still be completed to provide pre and post-stimulation variations.