This study uses imaging to evaluate how LY3372689 binds to a protein in the brain. This study will be conducted in healthy participants and will last up to approximately 25 days after enrollment. Screening must be completed within 28 days prior to enrollment.

Inclusion Criteria:

• Overtly healthy males or females who cannot get pregnant
• Have a body mass index (BMI) of at least 18.5 kilogram per square meter (kg/m²), inclusive, at screening
• Have normal blood pressure, pulse rate, electrocardiogram (ECG, heart tracing), blood and urine laboratory test results that are acceptable for the study
• Have veins and arteries suitable for protocol required blood sampling

Exclusion Criteria:

• Have a history of head injury or contraindications to undergoing magnetic resonance imaging (MRI) examination
• Are currently participating in or completed a clinical trial within the last 30 days or any other type of medical research judged to be incompatible with this study
• Have previously participated or withdrawn from this study
• Smoke more than the equivalent of 10 cigarettes per day and are unwilling to stop smoking for study procedure
• Have or used to have health problems or laboratory test results or ECG readings that, in the opinion of the doctor, could make it unsafe to participate or could interfere with understanding the results of the study
• Have long exposure to sunlight routinely or use tanning beds regularly
• Participate in regular vigorous exercise