This is a cross-over randomized study to validate the Sponsor investigational medical device against measurements of glymphatic function from MRI-based neuroimaging, EEG, blood biomarkers and cognitive tests in healthy older volunteers.

The study population will consist of healthy individuals, ages 55 to 65, that are cognitively normal and do not have a medical history of neurological or sleep disorder, cardiovascular disease, hypertension, or diabetes. The objectives of this study are to define whether sleep- and wake-associated device measurements (i) faithfully reflect glymphatic function measured by gold-standard contrast enhanced MRI and non-invasive MRI-based measures of glymphatic function; (ii) replicate pre-clinical findings between sleep EEG power bands and glymphatic flow; (iii) predict plasma levels of Alzheimer's disease (AD)-related biomarkers; and (iv) predict morning cognitive performance.

Inclusion Criteria:

1. Participants must have a Montreal Cognitive Assessment (MoCA) score at least 26.
2. Participants must have a Geriatric Depression Scale (GDS) 15-item score of 4 or less.

Exclusion Criteria:

1. Participants with a formal diagnosis of any sleep disorder (e.g., sleep apnea on positive-airway-pressure (PAP) therapy, insomnia, restless leg syndrome, circadian rhythm sleep disorder, parasomnia).
2. Participants with a history of significant neurological disease or history of epilepsy.
3. Participants with cardiovascular disease or cardiovascular risk factors (smoking or hypertension).
4. Participants with diabetes.
5. Participants with traumatic brain injury, or serious mental illness including bipolar disorder, schizophrenia, major depressive disorder or post-traumatic stress disorder.
6. Participants who have taken in the past 30 days prescribed or overthe- counter (OTC) stimulants, sleeping medications, or psychiatric medications including antidepressants.
7. Participants who consume more than 400 mg/day of caffeine. Participants will be required to not consume caffeine beginning 12pm on the day-of the sleep study.
8. Female Participants who consume more than 3 alcoholic drinks on any day or more than 7 drinks per week. Male participants who consume more than 4 alcoholic drinks on any day or more than 14 drinks per week.
9. Participants planning travel to alternate time zones within two weeks of study participation
10. Participants with travel plans or conflicts that would prevent them from either Study Visit.
11. Participants who are enrolled in other research studies and are receiving an investigational drug within 30 days of the planned start date.
12. Participants who have any condition that, in the opinion of the Sponsor Principal Investigator, would compromise the well-being of the participant or the study or prevent the participant from meeting or performing study requirements.
13. Participants with absolute or relative contraindications to MRI imaging based on current up-to-date screening questionnaires including claustrophobia, inability to lie still on their back for 30-45 minutes or require sedation prior to the MRI.
14. Participants with a head circumference greater than 60 cm that would prevent use of a high-resolution 64 channel MRI head coil required for this study
15. Participants who have a pre-planned surgery or medical procedure that would interfere with the conduct of the study.
16. Participants who have an implanted medical device or contraindications that would exclude MRIs
17. Participants with a serious infection requiring medical attention in the past 30 days
18. Participants with a diagnosis of substance use-disorder in the past 2 years.
19. Participants with known acute or chronic kidney disease and/or compromised GFR.

Visit type was masked to neuroimaging assessors and blood biomarker analysis laboratory