A Study of JNJ-64042056 in Participants With Preclinical Alzheimer's Disease

Inclusion Criteria:

• Elevated brain tau pathology defined as Braak 3 region of interest standardizeduptake value ratio (ROI SUVR) greater than (>) 1.1 (or equivalent based on emergingdata) on a screening tau PET scan, reviewed centrally by a qualified reader toenrich for probability of disease progression during the study

• Clinical Dementia Rating (CDR) global score of 0 at screening and baseline

• Mini Mental State Examination (MMSE) greater than or equal to (>=) 27 (witheducational adjustment) at screening

• Able to read and write and with a minimum 5 years of formal education as reported byparticipant and study partner at screening

• A participant must be of non-childbearing potential

Exclusion Criteria:

• History consistent with or known autosomal dominant AD (mutation identified in thefamily and/or participant)

• Fulfills diagnostic criteria for Alzheimer's Dementia or non-Alzheimer's Dementia,including, but not limited to Frontotemporal Dementia (FTD), Diffuse Lewy BodyDementia (DLBD), Vascular Dementia (VAD), alcoholic dementia, Parkinson's dementia,Korsakov, Creutzfeldt-Jakob or other prion diseases, Posterior Cortical Atrophy

• Diagnosis of Mild Cognitive Impairment (MCI)

• Vitamin B12 or folate levels below the central laboratory lower limit of normal,unless the investigator determines that supplementation is not required afterrandomization

• History of or current neurological disease other than preclinical AD that may makeinterpretation of possible new neurological signs or symptoms difficult