A Double-Blind, Placebo-Controlled Safety and Efficacy Study of NA-831

1. Is male or female, at 55-85 years of age (inclusive) at screening self-reported memory complaint, corroborated by spouse or companion as appropriate.
2. Wechsler Memory Scale III (WMS-III) age-adjusted Logical Memory II score ≤ 5.
3. Mini-Mental State Exam (MMSE) ≥23
4. Center for Epidemiologic Studies-Depression (CES-D) score \<27.
5. Normal thyroid function, defined as TSH, T3 and T4 within normal limits.
6. Agree not to consume alcoholic beverages within 8 hours of each study visit.
7. Willing and able to sign informed consent and complete the CTB and all other tests and procedures as listed in the protocol.
8. Able to read at a 6th grade level or equivalent
9. Female subjects must be surgically sterile or post-menopausal for at least 2 years. If \<2 years post-menopausal, then a follicle stimulating hormone (FSH) ≥40 mIU/mL must be obtained.
10. If participant is receiving an acetylcholinesterase inhibitor or memantine, the dose must have been stable for at least three months before Screening
11. Must have a reliable and competent trial partner/informant who has a close relationship with the participant and is willing to accompany the participant to all required trial visits, and to monitor compliance of the administration of the trial medication

EXCLUSION CRITERIA

1. Subjects who have any significant, untreated psychiatric illness or any CNS condition (such as schizophrenia, Parkinson's disease, stroke, etc.) that could interfere with the study evaluations or procedures or which poses an additional risk.
2. Evidence of a clinically relevant or unstable psychiatric disorder, excluding major depression in remission
3. History of significant head trauma followed by persistent neurologic defaults or known structural brain abnormalities.
4. Have had a stroke or Transient Ischemic Attack (TIA) or unexplained loss of consciousness in the past 1 year
5. History of seizures or epilepsy within the last 5 years
6. History of hepatitis or liver disease that has been active within the 6 months prior toScreening
7. History of malignancy occurring within the 5 years before Screening, except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or localized prostate carcinoma
8. Clinically significant vitamin B12 or folate deficiency in the 6 months before Screening
9. History of unstable angina, myocardial infarction, chronic heart failure or clinically significant conduction abnormalities within 1 year prior to Screening Visit
10. History of alcohol or substance abuse or dependence within the past year.
11. Has human immunodeficiency virus (HIV) by medical history
12. Acute infective sinusitis.
13. History or presence of an abnormality of the external or internal structures of the nose or nasopharynx, except for surgical correction of the nasal septum or a "broken nose" at least 2 years previously, or surgical repair of cleft palate when \<30 years of age.
14. Use of medications that are known to cause frank obtundation of cognition
15. History of or current significant systemic disease judged to interfere with the study evaluations or likely to be a safety concern.
16. Untreated sleep apnea or treatment for sleep apnea for \<3 months.
17. Clinically significant systemic illness or serious infection within 30 days prior to or during the screening period
18. Use of allowed medications for chronic conditions at doses that have not been stable for at least 4 weeks prior to Screening, or use of AD medications at doses that have not been stable for at least 8 weeks prior to Screening
19. Abnormal clinical laboratory test results, specifically: Alanine transaminase (ALT) or aspartate transaminase (AST) >2 х the upper limit of normal (ULN),Hematology \<80% the lower limit of normal, Creatinine ≥2 mg/dL and ,Other clinical laboratory values or vital signs considered clinically significant in the opinion of the Investigator.
20. Treatment with any investigational drug, biologic, or device within the previous 30 days prior to screening.
21. Surgery involving general anesthesia within the past 3 months or planned surgery requiring general anesthesia during the study period.
22. Contraindications to study procedures
23. Use of any medications that, in the opinion of the Investigator, may contribute to cognitive impairment, put the participants at higher risk for adverse events (AEs), or impair the participant's ability to perform cognitive testing or complete study procedures.