This is a single-center, open-label study designed to evaluate the feasibility, safety, and preliminary efficacy of cerebellar adaptive deep brain stimulation (aDBS) in adults with spinocerebellar ataxia type 6 (SCA6). A total of 5 participants will be enrolled.

Participants will undergo surgical implantation of deep brain stimulation (DBS) leads targeting the motor interposed nucleus of the cerebellum. The leads will be connected to one or two implantable pulse generators capable of delivering stimulation to deep brain structures and recording neural activity.

Participants will complete up to 18 in-person study visits over a 24-month follow-up period. During these visits, neural signals will be recorded under varying behavioral tasks and stimulation conditions.

Early study visits will be used to identify optimal stimulation parameters and neural biomarkers associated with disease state. These biomarkers will subsequently be used to implement adaptive DBS, in which stimulation amplitude is automatically adjusted in response to recorded neural activity.

Study outcomes will include assessments of safety and feasibility of cerebellar aDBS, as well as preliminary evaluation of its effects on clinical measures.

Inclusion Criteria:

• A diagnosis of SCA6 by a movement disorders specialist following established criteria recommended by the Movement Disorders Society
• A positive genetic test for SCA6
• A total score ≥ 8 on the Scale of the Assessment and Rating of Ataxia (SARA) rating scale
• Ability to walk with or without support (score <8 on the 'gait' subsection of the SARA rating scale)
• Age ≥ 21 years and <89 years
• Ability to give informed consent for the study
• Ability to understand the study protocol

Exclusion Criteria:

• Inability or unwillingness to comply with the study protocol

• History of previously implanted neurostimulators, pacemakers, defibrillators, or metallic head implants

• Severe cognitive impairment or dementia, defined as a score <21 on the Montreal Cognitive Assessment (MOCA)

• Evidence of ataxia due to other etiologies, including but not limited to:

  • Genetic/inherited disorders other than SCA6
  • Acquired causes: traumatic brain injury, multiple sclerosis, paraneoplastic cerebellar degeneration, infections or post-infectious cerebellitis, autoimmune ataxias (e.g., anti-GAD, gluten ataxia)
  • Toxic/metabolic causes: alcoholic cerebellar degeneration, vitamin deficiencies
  • Structural, vascular, or neoplastic causes: cerebellar stroke, tumors, congenital malformations
  • Suspected multiple system atrophy-cerebellar type (MSA-C)

• Presence of active and untreated psychiatric illness, severe depression (Beck Depression Inventory ≥ 21), or personality disorder at the discretion of the study team

• Coagulopathy, uncontrolled epilepsy, or other medical conditions that are considered to place the patient at elevated risk for surgical complications

• Presence of a concomitant medical condition that, in the investigator's opinion, may interfere with the study participation or gait/balance, for example, severe arthritis

• Requirement of diathermy, electroconvulsive therapy, or transcranial magnetic stimulation

• Pregnancy or lactation

• Active suicidal ideation, defined as fined as a "Yes" response to questions #2-5 within the past one month on the Columbia Suicide Severity Rating Scale, C-SSRS

• Refractory epilepsy