A Clinical Trial of LY3962681 in Healthy Volunteers and in Patients With Parkinson's Disease

Inclusion Criteria:

• Participant is overtly healthy as determined by medical evaluation. Rescreening isallowed in this study.

• A Montreal Cognitive Assessment score greater than or equal to 24.

• Stable use of background medications at least 8 weeks prior to IP administration,including but not limited to those used for treatment of Parkinson's disease (including deep brain stimulation), and the investigator must expect thatparticipant can tolerate a minimum of 6 months without dose adjustment.

MAD study only

• Participant has a diagnosis of Parkinson's disease per UK Parkinson's DiseaseSociety Brain Bank Clinical Diagnostic Criteria.

• Modified Hoehn and Yahr Stage 1 to 2.5 in the practically defined OFF state.

• A positive result on CSF alpha-synuclein Seed Amplification Assay. (A prior positiveresult [within 1 year of screening] accepted with sponsor approval if patient didnot participate in another Parkinson's disease clinical trial during this period.) (US and Japan only)

• UPSIT score of 10 percentile or less, corrected for age and sex (EU and UK only).

• An abnormal DaT-SPECT consistent with parkinsonism. (History of an abnormal DaTSPECTwith the report confirmed by study investigator will be accepted.)

• For participants not taking Parkinson's disease medications, not expected toinitiate treatment within 6 months.

• Have a body weight within 40 kg (88 pounds) to 110 kg (242 pounds), inclusive, andbody mass index within the range of 17 to 34 kg/m^2, inclusive.

Exclusion Criteria:

• MAD study only: Significant neurological disease affecting the central nervoussystem other than Parkinson's disease that may be a cause for the participant'sclinical symptoms or may confound study objectives.

• Current concomitant disease or serious or unstable illnesses, including centralnervous system (SAD study only), cardiovascular, hepatic, renal, gastroenterology,respiratory, endocrinologic, neurologic (MAD study only: other than Parkinson'sdisease), psychiatric, immunologic, or hematologic disease and other conditionsthat, in the investigator's opinion, could interfere with the conduct of the studyor that would, in the opinion of the investigator, pose an unacceptable safety riskto the participant.

• Participant is generally frail or has any medical disorders that, in the opinion ofthe investigator, could interfere with study-related procedures (including safeperformance of IT injection or LP), such as prohibitive spinal diseases, bleedingdiathesis, clinically significant coagulopathy, thrombocytopenia, or increasedintracranial pressure.

• Have a 12-lead ECG abnormality at screening that, in the opinion of theinvestigator, increases the risks associated with participating in the study or mayconfound ECG data analysis.

• MAD study only: Treatment with continuous intestinal delivery Parkinson's diseasemedication (for example, Duodopa).

Other protocol-defined inclusion/exclusion criteria may apply.