The primary objective of the study is to evaluate the pharmacokinetic (PK) comparability of 2 fixed subcutaneous (SC) doses of aducanumab with a single, weight-based intravenous (IV) dose of aducanumab in healthy volunteers. The secondary objectives of the study are to assess the safety and tolerability of aducanumab administered SC in healthy volunteers and to characterize additional PK parameters of 2 fixed SC doses of aducanumab and a single, weight-based IV dose of aducanumab.

Key Inclusion Criteria:

• Have a body mass index between 18 and 30 kilograms per meter square (kg/m^2), inclusive
• Japanese participant has both biological parents and all 4 grandparents of Japanese descent
• Have a negative polymerase chain reaction test result for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on Day -1

Key Exclusion Criteria:

• History of any clinically significant cardiac, endocrine, gastrointestinal, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, or renal disease, or other major disease, as determined by the Investigator
• History of severe allergic, anaphylactic or systemic hypersensitivity reactions, or of any allergic reactions that in the opinion of the Investigator are likely to be exacerbated by aducanumab, the excipients contained in the formulation, and if appropriate, any diagnostic agents to be administered during the study
• History of, or positive test result at Screening for, human immunodeficiency virus
• History of hepatitis C infection or positive test result at Screening for hepatitis C virus antibody
• Symptoms consistent with SARS-CoV-2 infection, per the judgment of the Investigator, within 14 days prior to Day -1, including but not limited to fever (temperature > 37.5 degrees Celsius [°C]), sore throat, new and persistent cough, shortness of breath, diarrhea, muscle aches, or loss of taste or smell
• Current enrollment in any other drug, biological, device, or clinical study, or treatment with an investigational drug or approved therapy for investigational use within 30 days prior to Day -1, or 5 half-lives, whichever is longer
• Any immunization or vaccination given within 10 days prior to administration of study treatment and for 10 days after administration of study treatment
• Mini mental state examination score of < 27 at Screening

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.

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