This is a longitudinal, triple-blind, randomized-controlled, prospective interventional study assessing patients with cerebellar ataxia, including spinocerebellar ataxia type 3 (SCA3) and multiple system atrophy-cerebellar type (MSA-C), to examine the efficacy, safety, and tolerability of transcranial alternating current stimulation (tACS) for up to 3 months.

Transcranial alternating current stimulation (tACS) is a relatively recent method that noninvasively modulates brain oscillations, and can effectively stimulate deep brain regions, affect brain rhythm, increase neural plasticity, change neurotransmitter levels, and improve brain function. It is a comfortable, safe, effective, non-invasive, and easy-to-operate method, which means it has development potential in relevant medical fields. It has been approved by the FDA for clinically treating neuropsychiatric diseases.

This is a prospective, longitudinal, triple-blind, randomized-controlled, interventional study designed to evaluate the efficacy, safety, and tolerability of tACS in patients of SCA3 and MSA-C in China. Based on typical guidelines, we will use the tACS paradigm (bilateral mandible as a place for active electrode stimulation electrode, and the inion for the return electrode). This study has two parts. The patients studied in the Part Ⅰ are SCA3. The patients studied in the Part Ⅱ are MSA-C. Every part of study, subjects will be randomized into two groups, one receiving a 10-day (5 days/week for 2 weeks) treatment with real cerebellar tACS (CB-tACS) and the other receiving a sham stimulation. The patient's motor function, cognitive function, sleep, mental state, plantar pressure, and magnetic resonance imaging will be assessed before and after the intervention.

There will be a total of 4 visits. All patients receiving tACS will be visited face to face at baseline, day 1, day 30, and day 90 after the treatment begins.

Inclusion Criteria:

• for SCA3

  • Patients with detectable clinical signs and confirmed genetic diagnosis with SCA3
  • SCA3 patients aged 18 - 80 years
  • Patients or their family members have informed consent to the study and signed relevant documents
  • The pre-study ataxia Assessment Score (SARA) ranged from 3 to 30

• for MSA-C

  • Aged 30-80 years
  • Diagnosed as clinically determined (Established)MSA-C or clinically Probable MSA-C according to the latest MSA diagnostic criteria
  • No more than 8 years after diagnosis of MSA-C
  • Able to walk independently or with assistance
  • Have a life expectancy of at least 3 years
  • Women of childbearing age with MSA need to use contraceptive measures

Exclusion Criteria:

1. Patients who have concomitant epilepsy.

2. Patients with a serious cognitive disorder, behavioral disorder, or mental illness

3. Patients with a history of seizures, stroke, encephalitis, or other degenerative neurological diseases

4. Patients with a serious medical disease

   • Patients who concomitantly suffer from severe renal impairment, convulsions, stomach ulcers, or moderate or more severe liver disease
   • Patients with uncontrolled high blood pressure or diabetes

5. History of head injury or neurosurgical interventions.

6. History of any metal in the head (outside the mouth).

7. Known history of any metallic particles in the eye, implanted cardiac pacemaker, implanted neurostimulators, surgical clips (above the shoulder line), or any medical pumps.

8. Patients who have taken other investigational products within 4 weeks before being enrolled in this clinical trial, or patients who are pregnant or breastfeeding.