If the optional bridging period is conducted, participants in Part A could be enrolled in the separate potential study for up to approximately 120 weeks. conditions: Alzheimer Disease studyType: INTERVENTIONAL phases: PHASE1 allocation: RANDOMIZED interventionModel: PARALLEL primaryPurpose: BASIC_SCIENCE masking: DOUBLE whoMasked: PARTICIPANT whoMasked: INVESTIGATOR count: 60 type: ESTIMATED name: LY3954068 name: Placebo name: Flortaucipir F18 measure: Part A: Number of participants with one or more Adverse Event (s) (AEs), Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Event(s) (SAEs) considered by the investigator to be related to study drug administration measure: Part B: Number of participants with one or more Adverse Event (s) (AEs), Treatment Emergent Adverse Events (TEAEs) and Serious Adverse Event(s) (SAEs) considered by the investigator to be related to study drug administration measure: Part A: Pharmacokinetics (PK): Maximum Observed Concentration (Cmax) measure: Optional Part B: PK: Cmax measure: Part A: PK: Area Under the Concentration Versus Time Curve (AUC) measure: Optional Part B: PK: AUC measure: Part A: PK: Cerebrospinal Fluid (CSF) concentration of LY3954068 measure: Optional Part B: PK: CSF concentration of LY3954068 measure: Part A: Pharmacodynamics (PD): Change from Baseline of CSF tau measure: Optional Part B: PD: Change from Baseline of CSF tau sex: ALL minimumAge: 50 Years maximumAge: 85 Years stdAges: ADULT stdAges: OLDER_ADULT facility: K2 Medical Research LLC city: Maitland state: Florida zip: 32751 country: United States role: CONTACT phone: 407-500-5252 name: Brandon Lenox role: PRINCIPAL_INVESTIGATOR lat: 28.62778 lon: -81.36312 facility: Charter Research, LLC city: The Villages state: Florida zip: 32162 country: United States role: CONTACT phone: 352-775-1000 name: Jeffrey Norton role: PRINCIPAL_INVESTIGATOR lat: 28.93408 lon: -81.95994 facility: Indiana University School of Medicine - Clinical Research Center city: Indianapolis state: Indiana zip: 46202 country: United States role: CONTACT phone: 317-963-7505 name: Jared Brosch role: PRINCIPAL_INVESTIGATOR lat: 39.76838 lon: -86.15804 facility: Massachusetts General Hospital (MGH) city: Charlestown state: Massachusetts zip: 02129 country: United States role: CONTACT phone: 617-643-5607 name: Steven Arnold role: PRINCIPAL_INVESTIGATOR lat: 42.37787 lon: -71.062 facility: CenExel AMRI city: Toms River state: New Jersey zip: 08755 country: United States role: CONTACT phone: 732-341-9500 name: Sanjiv Sharma role: PRINCIPAL_INVESTIGATOR lat: 39.95373 lon: -74.19792 facility: Duke University city: Durham state: North Carolina zip: 27710 country: United States name: Shruti Raja role: PRINCIPAL_INVESTIGATOR lat: 35.99403 lon: -78.89862 facility: Medical College of Wisconsin city: Milwaukee state: Wisconsin zip: 53226 country: United States role: CONTACT phone: 414-955-0650 name: Malgorzata Franczak role: PRINCIPAL_INVESTIGATOR lat: 43.0389 lon: -87.90647 facility: The University of Tokyo Hospital city: Bunkyo-ku state: Tokyo zip: 113-8655 country: Japan role: CONTACT phone: +81-33-815-5411 name: Takeshi Iwatsubo role: PRINCIPAL_INVESTIGATOR lat: 35.37517 lon: 139.92991 facility: National Hospital for Neurology and Neurosurgery (UCLH) city: London zip: WC1N 3BG country: United Kingdom role: CONTACT phone: 0203 448 3011 name: Catherine Mummery role: PRINCIPAL_INVESTIGATOR lat: 51.50853 lon: -0.12574 facility: Royal Hallamshire Hospital city: Sheffield zip: S10 2JF country: United Kingdom name: Daniel Blackburn role: PRINCIPAL_INVESTIGATOR lat: 53.38297 lon: -1.4659 facility: University Hospital Southampton city: Southampton zip: SO16 6YD country: United Kingdom name: Christopher Kipps role: PRINCIPAL_INVESTIGATOR lat: 50.90395 lon: -1.40428 hasResults: False