Transcutaneous Auricular Vagus Nerve Stimulation to Improve Upper Extremity Recovery After Traumatic Brain Injury

Upper extremity impairments are among the most disabling long-term consequences of traumatic brain injury (TBI). Weakness, impaired motor control, reduced dexterity, spasticity, and limited functional arm and hand use can restrict independence, community participation, and return to meaningful life roles. Functional task-specific practice (FTP) is a task-oriented, activity-based rehabilitation approach that uses repeated practice to improve gross upper extremity movement, isolated finger motion, and pinch and grasp needed for daily activities. Despite rehabilitation, many individuals with moderate-to-severe TBI continue to have substantial upper extremity limitations, supporting the need for strategies that may enhance the effects of rehabilitation.

Vagus nerve stimulation (VNS) activates afferent vagal fibers and downstream brainstem nuclei, including the locus coeruleus and basal forebrain. These systems regulate norepinephrine and acetylcholine release and support cortical excitability, attention, learning, long-term potentiation, and task-dependent plasticity. Implanted VNS paired with upper extremity rehabilitation has improved motor outcomes after stroke, but it requires surgery and ongoing device management.

Transcutaneous auricular vagus nerve stimulation (taVNS) is a non-invasive approach that delivers electrical stimulation through surface electrodes placed on the external ear. Studies in stroke suggest that taVNS paired with upper extremity practice is feasible, generally well tolerated, and may enhance upper extremity recovery and task-related cortical activation. taVNS has not been adequately studied for upper extremity recovery after TBI. Because stroke and TBI may share network-level disruptions relevant to motor and cognitive recovery, a pilot sham-controlled trial is warranted to evaluate safety, feasibility, and preliminary effects in TBI.

The overall objective is to evaluate taVNS paired with upper extremity FTP after TBI. The study will also explore effects on cognition and cortical activation measured with functional near-infrared spectroscopy (fNIRS).

Aim 1: Safety, tolerability, and feasibility Evaluate the safety, tolerability, and feasibility of taVNS paired with upper extremity rehabilitation after TBI. The intervention will be considered feasible if more than 80% of participants complete at least 80% of prescribed sessions, with fewer than 10% withdrawing because of taVNS. Mean stimulation-related discomfort is expected to be 4 or less on a 0-10 Numeric Rating Scale, and fewer than 10% of participants are expected to experience device- or protocol-related adverse events.

Aim 2: Preliminary motor effects Compare changes in upper extremity strength and function between participants receiving active taVNS plus FTP and those receiving sham taVNS plus FTP. Active taVNS is hypothesized to produce greater improvement in Action Research Arm Test (ARAT), Box and Blocks Test, and Fugl-Meyer Assessment upper extremity scores and a more favorable Participant Global Impression of Change (PGIC).

Aim 3: Exploratory cognitive and cortical effects Explore changes in cognitive performance using the Brief Test of Adult Cognition by Telephone (BTACT) and Mini-Mental State Examination (MMSE) and evaluate within-participant differences and between group differences in cortical activation during FTP with and without active taVNS using fNIRS.

• taVNS (Device): Participants assigned to active taVNS will receive stimulation through an earbud electrode positioned on the auricular concha. Current intensity will be individually adjusted to a tolerable level. Stimulation may be reduced, paused, or stopped for discomfort or safety concerns.
• FTP (Other): Both groups will receive the same structured upper extremity rehabilitation program. Each 60-minute session will include approximately 40 minutes of upper extremity FTP and 10 minutes of functional carryover activities in a real-world or simulated context, with remaining time used for setup, monitoring, and transition. Training will target gross upper extremity movement, bilateral pinch, bilateral grasp, unilateral grasp, complex or unilateral pinch, and finger isolation. Progression may include increased repetitions or speed, resistance, reduced therapist assistance, and varied task contexts using common objects.

Primary outcomes

• Safety of intervention [From enrollment to the end of treatment at 4 weeks]: Number, type, severity, study-relatedness, action taken, and outcome of adverse events.
• Tolerability of intervention [From enrollment to end of treatment at 4 weeks]: Stimulation-related discomfort using a 0-10 Numeric Rating Scale during sessions; reasons for pauses or discontinuation.
• Feasibility of intervention [From enrollment to end of treatment at 4 weeks]: Frequency counts and percentages will be used to summarize the number of adverse events, and participant's session completion and dropout rate to assess for safety, feasibility, and adherence.
• Fugl-Meyer Assessment Upper Extremity (FMA-UE) [Baseline and 4 weeks]: A standardized clinical assessment used to evaluate motor impairment and recovery of the arm and hand following neurological injury. The upper extremity portion assesses movement, coordination, reflex activity, and hand function. During the assessment, participants are asked to perform a series of arm, wrist, and hand movements while a trained examiner observes and scores performance. Tasks include movements such as shoulder elevation, elbow flexion and extension, wrist motion, grasping objects, and finger movements. Scores are on a scale of 0-2 based on the participant's ability to successfully complete each movement, and a higher score indicates better performance. The assessment is commonly used in rehabilitation research to quantify upper extremity motor impairment and recovery. Administration typically requires approximately 20-30 minutes.
• Action Research Arm Test (ARAT) [Baseline and 4 weeks]: A standardized assessment of upper extremity functional ability. It evaluates a participant's capacity to perform tasks involving grasp, grip, pinch, and gross arm movement. Participants are asked to manipulate a variety of commonly used objects of different sizes, shapes, and weights, such as blocks, balls, and tubes. Tasks include picking up, moving, and placing objects as well as performing gross reaching movements. Performance is scored according to the participant's ability to complete each task within specified time limits. The ARAT provides an objective measure of upper extremity functional performance and is widely used in neurological rehabilitation research. Administration typically requires approximately 10-20 minutes.
• Box and Block Test (BBT) [Baseline and 4 weeks]: A standardized measure of manual dexterity and gross hand function. During the test, participants sit in front of a box divided into two compartments containing small wooden blocks. Participants are instructed to move as many blocks as possible, one at a time, from one compartment to the other using one hand during a 60-second period. The test is completed separately for each hand. The primary outcome is the number of blocks successfully transferred within the allotted time. The BBT is commonly used to assess hand dexterity and upper extremity function in individuals with neurological and musculoskeletal conditions. Administration typically requires approximately 5 minutes.
• Patient Global Impression of Change (PGIC) [End of treatment at 4 weeks]: A patient-reported outcome measure used to assess an individual's perceived change in upper extremity function following treatment. At the post-treatment assessment, participants will be asked to rate how their arm and hand function has changed since the start of the study using a 7-point scale. Response options range from "very much worse" to "very much improved", and a higher score indicates greater perceived function. The PGIC captures the participant's overall perception of meaningful functional change and complements objective clinical measures of upper extremity performance. The assessment consists of a single question, requires approximately 1 minute to complete, and poses minimal risk to participants.

Secondary outcomes

• Brief Assessment of Cognition and Treatment (BTACT) [Baseline and 4 weeks]: A brief cognitive assessment battery designed to evaluate cognitive functioning across multiple domains. The assessment includes measures of episodic memory, working memory, processing speed, reasoning, executive functioning, verbal fluency, and attention. The BTACT can be administered in a relatively short period of time and provides a broad assessment of global cognitive function. The measure will be administered at baseline and post-treatment to assess cognitive status and explore changes in cognitive performance over the course of study participation. Higher scores generally reflect better cognitive functioning.
• Mini-Mental State Examination (MMSE) [Baseline and 4 weeks]: A widely used cognitive screening instrument that provides a brief assessment of global cognitive functioning. The MMSE evaluates several cognitive domains, including orientation, attention, concentration, immediate and delayed memory, language, and visuospatial abilities. The assessment consists of a series of structured questions and tasks and yields a total score ranging from 0 to 30, with higher scores indicating better cognitive functioning. The MMSE will be administered at baseline and post-treatment to characterize participants' cognitive status and to assess for changes in overall cognitive functioning following the intervention. The MMSE is commonly used in clinical and research settings as a screening measure for cognitive impairment.
• Functional near-infrared spectroscopy (fNIRS) [Baseline and 4 weeks]: A non-invasive neuroimaging technique that measures changes in cerebral blood oxygenation associated with cortical brain activity. During study assessments, participants will wear a lightweight fNIRS cap containing near-infrared light sources and detectors positioned over specific regions of the scalp. The fNIRS system continuously records changes in oxygenated hemoglobin (HbO), deoxygenated hemoglobin (HbR), and total hemoglobin (HbT) while participants perform FPT. The primary fNIRS-derived outcomes include changes in oxygenated, deoxygenated, and total hemoglobin concentrations within targeted cortical regions during FTP conditions. These measures provide information regarding cortical activation patterns and neurophysiological responses associated with upper extremity task performance and rehabilitation. fNIRS data collection typically occurs concurrently with task performance and is expected to last approximately 20-30 minutes. The procedure is associated with minimal risk.
• Brief Symptom Inventory-18 (BSI-18) [Baseline and 4 weeks]: A brief self-report questionnaire used to screen for psychological distress and psychiatric symptoms. The measure consists of 18 items that assess the degree to which participants have been bothered by various symptoms during the past seven days. Items are rated on a 5-point Likert scale ranging from 0 ("not at all") to 4 ("extremely"). The BSI-18 yields a Global Severity Index (GSI) as an overall measure of psychological distress, as well as three symptom subscales: Somatization, Depression, and Anxiety. Higher scores indicate greater psychological symptom burden. A higher score indicates greater distress and symptoms. The BSI-18 will be used to characterize participants' emotional and psychological functioning and to monitor symptoms that may influence rehabilitation participation and outcomes.
• DSM-5 Level 1 Cross-Cutting Symptom Measure (Adult) [Baseline and 4 weeks]: A brief self-report screening instrument developed by the American Psychiatric Association to assess psychiatric symptoms across multiple mental health domains. The measure evaluates symptoms experienced during the previous two weeks across domains including depression, anger, mania, anxiety, somatic symptoms, suicidal ideation, psychosis, sleep problems, memory concerns, repetitive thoughts and behaviors, dissociation, personality functioning, and substance use. Responses are provided on a 5-point scale where a higher score reflects greater symptom frequency or severity. The measure is intended to identify clinically relevant symptoms that may warrant further evaluation and provides a broad assessment of mental health symptoms. The DSM-5 Cross-Cutting Symptom Measure will be used to characterize participants' psychiatric symptom profiles and identify factors that may influence study participation, treatment response, or rehabilitation outcomes.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Age 18 years or older.
* History of TBI requiring inpatient rehabilitation, with resulting upper extremity impairment in at least one limb
* Passive range of motion within functional limits at the wrists, shoulders, and elbows.
* Able to attend on-site training at Craig Hospital three times per week for four weeks.
* No complicating physical or cognitive condition, as determined by the physician or study investigator, that would preclude safe use of taVNS.
* If taking prescribed antispasticity medication, dose stable for at least four weeks before study procedures.
* Able to provide informed consent.

Exclusion Criteria:

* Recent fracture or contracture that could interfere with the intervention.
* Botulinum toxin injections to the upper extremity or hand within the previous three months.
* Pregnant, planning pregnancy, or breastfeeding.
* Concurrent participation in another drug or device trial that may interfere with this study.
* Implanted pacemaker, spinal cord stimulator, ventriculoperitoneal shunt, deep brain stimulator, or intrathecal pump.
* Any condition or circumstance that, in the investigator's judgment, makes participation unsafe or inappropriate.

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