The primary objectives of this study are to evaluate the absolute bioavailability of a single, fixed sub-cutaneous (SC) dose of aducanumab compared with a single, weight-based intra-venous (IV) dose in healthy participants and to characterize the pharmacokinetics (PK) profile of aducanumab. The secondary objectives are to evaluate the safety and tolerability of aducanumab administered via SC and IV routes in healthy participants and to characterize additional PK parameters of a single, fixed SC dose of aducanumab and a weight-based IV dose in healthy participants.