Safety, Tolerability, and Pharmacokinetics Study of ATH-1020

Inclusion Criteria: All Subjects

1. Body mass index (BMI) of ≥ 18.0 and ≤ 32.0 kg/m2 at Screening, with minimum weight of 60 kg.
2. Subjects in generally good health per the investigator's discretion.
3. Male subjects and their partners must be willing to comply with the contraceptiverequirements of the study.
4. Subjects must have adequate venous access. Part A (SAD)
5. Male subjects aged 18 to 50 years at the time of signing the informed consent. Part B (MAD)
6. Male subjects aged 18 to 50 years (Cohorts B1, B2, B3, and B5); male andpost-menopausal female subjects aged 65 to 85 years (Cohort B4) at the time of signingthe informed consent.

Exclusion Criteria:

1. History of significant drug allergies (including to any excipients) or of anaphylacticreaction.
2. Any condition per the investigator's discretion, which while not requiring chronicmedication use, is likely to require intermittent/acute therapeutic intervention.
3. Any history of seizures or loss of consciousness for an unknown reason.
4. History of or positive results of serology screening for hepatitis B, hepatitis C orhuman immunodeficiency virus (HIV).
5. Abnormal liver tests
6. Impaired renal function.
7. History of having taken another investigational drug within 30 days prior to Admission (Day -1).
8. Major surgery within 90 days prior to Admission (Day -1) or anticipated surgery duringthe study. Part A (SAD)
9. Female subjects are not permitted.
10. Any medical condition that requires chronic medication use. Part B (MAD)
11. A history of intermittent benzodiazepine (short-acting only) or other treatments forinsomnia and anxiety are allowed, provided that the subject is able to abstain fromtheir use during the Screening period, and from Admission until discharge from thestudy.
12. Reported changes in cognition and reported history of declines in everyday life in thelast year. Part B (MAD) CSF Sampling (Cohort B5)
13. Subject history of or current contraindication to lumbar puncture/spinalcatheterization.
14. Clinically significant abnormalities in coagulation parameters.