A Phase 1, SAD and MAD Study to Evaluate the Safety and Tolerability of FB418

Key Inclusion Criteria: Healthy, adult, male 19 55 years of age, inclusive, at the screening. For elderly subjects(Part A Cohort 5 only), healthy, elderly, male or female (of non childbearing potential only) over 60 years of age, inclusive, at screening. In the case of the elderly(Part A Cohort 5 only), they have a history of mild disease, but can participate if the researcher judges that they can stop taking the drug at least 2 weeks before the expected first dose or before the half-life is 5 times or more) The continuous non smoker who have not used nicotine containing products for at least 3 months prior to (the first) dosing and throughout the study are based on subjective self reporting. Body mass index (BMI) ≥ 18 and ≤ 32 kg/m2 at the screening. Medically healthy with no clinically significant medical history, physical examination, simplified neurological examination, laboratory profiles, vital signs or ECGs, as deemed by the PI or designee. In Cohort 5, A female subject must be of non childbearing potential Key Exclusion Criteria: Is mentally or legally incapacitated or has significant emotional problems at the time of the screening visit or expected during the conduct of the study. History or presence of a clinically significant medical or psychiatric condition or disease in the opinion of the PI or designee. History of any illness that, in the opinion of the PI or designee, might confound the results of the study or poses an additional risk to the subject by their participation in the study. Is at suicidal risk in the opinion of the PI as per the following criteria: Any suicide attempts within 12 months prior to screening or any suicidal intent, including a plan, within 3 months prior to screening. C-SSRS answer of "YES" on suicidal ideation within 3 months prior to screening. History or presence of alcoholism or drug abuse within the past 2 years prior to (the first) dosing. History or presence of hypersensitivity or idiosyncratic reaction to the study drug or related compounds. History of seizures (childhood febrile seizures are excepted). Positive urine drug or alcohol results at screening or check in. Has an abnormal screening ECG indicating a second- or third- degree AV block, or one or more of the following: QRS > 120 msec, QTcF > 450 msec for males and > 460 msec for females, PR interval > 220 msec. Any rhythm other than normal sinus rhythm, which is interpreted by the PI or designee to be clinically significant at screening or check-in. Has any medical or surgical condition in which lumbar puncture is contraindicated in the opinion of the PI.