Participants will be administered single doses of study medication on Days 1 to 14. Following and/or during each dose level of the study (cohort), the observed safety and tolerability profile of the ongoing cohort and previous cohort will be evaluated and doses will only be increased if the observed safety and tolerability profile is acceptable. Plasma pharmacokinetic profiles of the ongoing cohort (up to and including Day 7) and plasma and cerebrospinal fluid (CSF) pharmacokinetic profiles as well as CSF plasma amyloid beta (Aβ) profiles of the previous cohort (up to and including Day 14) if applicable, will support dose increase decisions. Actual dose levels as well as the magnitude of dose escalation will depend on the results of the ongoing single-ascending dose study (54861911ALZ1001), the observed safety and tolerability profile, as well as the observed exposures. Participants will be discharged from the clinical unit after the last study assessment on Day 16 or approximately 24 hours after the indwelling catheter has been removed, whatever occurs later. If discharged on Day 16, participants will return to the clinical unit on Day 17 (72 hours post-dose Day 14) for plasma pharmacokinetic sampling. Safety assessments will be performed throughout the study. The maximal study duration for a participant will not exceed 8 weeks.