LY-3954068

The main purpose of this study is to evaluate the safety of LY3954068 in participants with early symptomatic Alzheimer's Disease (AD). The study will also investigate how much LY3954068 gets into the bloodstream and will test the effects of LY3954068 on markers of AD.
The study will be comprised of two parts, A and B. Part B is optional, and participants from Part A may also have the opportunity to join an optional bridging period to a separate potential study where participants would receive LY3954068. Each enrolled participant in Part A will receive a single dose of LY3954068 or placebo (no active drug) given into the spinal fluid. If conducted, each participant in Part B would receive 2 doses of either LY3954068 or placebo administered into the spinal fluid.
The study will last up to approximately 45 weeks for Part A, and, if conducted, 73 weeks for Part B, including the screening period.
If the optional bridging period is conducted, participants in Part A could be enrolled in the separate potential study for up to approximately 96 weeks, including the screening period.