Acceptability and Safety of MR-C-014 in Persons With Neuromyelitis Optica Spectrum Disorder

Inclusion Criteria: 1. Age 18-70 years of age (inclusive). 2. Able to read and/or understand English. 3. Meets revised diagnostic criteria for NMOSD proposed by the International Panel for NMO Diagnosis (IPND) in 2015. 4. Past clinical history of Transverse Myelitis as seen on imaging or as determined by clinical review by the investigator. 5. Demonstrates an observable gait deficit resulting from a diagnosis of NMOSD as determined by the Investigator or medical history review. 6. Currently able to walk at a speed greater or equal to 0.4 m/s, but less than 1.5 m/s, as determined by walking speed during a Timed 25-Foot Walk Test (T25FWT) (cane(s), walking stick(s), crutch(es), wheeled walker, external functional neuromuscular stimulator(s), and ankle foot orthosis allowed). a. Note: if assistive devices are planned to be used during the Intervention Phase walking sessions, they should be used during the Screening, Baseline, and Closing visit gait assessments as well. 7. Has a reciprocal gait pattern. a. Note: a non-reciprocal gait pattern is defined as a 3-point step pattern. Participants must have a 2-point step pattern to qualify. Asymmetry seen in gait is acceptable. 8. Ability and willingness to provide Informed Consent. Exclusion Criteria: 1. Unable or unwilling to comply with study protocol. 2. People who become pregnant or are pregnant (due to expected changes in gait patterns). 3. Unable to safely participate in protocol-defined walking sessions of 30-minute duration as determined by the investigator. 4. Significant co-morbid medical or neurological disease or injury, or treatment for such conditions that currently affects, or has potential to affect, participant gait for safety during participation in the study as determined by the investigator. 5. Has an external lower limb prosthetic ("artificial limb"). 6. Initiated physical therapy for lower limb in the past 4 weeks or anticipated to start due to safety concerns (e.g., falls). 7. Requires at least one seated rest during the T25FWT. 8. Initiation, change, or discontinuation of disease-modifying therapy in the past 3 months known to affect gait (e.g., dalfampridine, corticosteroid, medications for spasticity). 9. Recent NMOSD relapse (last 3 months) and/or hospitalization. 10. Severe hearing impairment with or without the use of hearing aids, such that the participant cannot hear the rhythmic music stimulus consistently, as determined by participant and investigator. 11. Treatment with a gait-based investigational intervention within the last 3 months. Enrollment in observational studies is allowed. 12. Vulnerable populations as deemed inappropriate for study by investigator. For this protocol, vulnerable persons are considered to be those who are relatively (or absolutely) incapable of protecting their own interests.