Despite the huge healthcare and economic impact of AD, there is still no disease modifying therapeutics available. In fact, the available therapeutics show low efficacy at best in the treatment of cognitive impairment in dementia. Development of a non-invasive medical device that is effective in slowing cognitive impairment is not only revolutionary but also possibly cost- effective. In this study, participants will come to MIT for a 1-day visit and the investigators will evaluate the effects of GENUS in cognitively normal, healthy adults. Investigators will use Electroencephalogram (EEG), Magnetoencephalography (MEG), magnetic resonance imaging (MRI), neuropsychological testing, and blood sampling in subsets of participants to evaluate for biological effects and safety of GENUS stimulation.

Information processing in the brain is thought to occur through synchronized neuronal activity in the form of network oscillations. Activity in the 30-100 Hz range is considered gamma-band oscillation and has been reported to be critical for attention, memory formation, and recall. Disruptions of gamma oscillations, particularly in the 30 - 50 Hz range, are reported as a potential early hallmark of Alzheimer's disease.

40Hz gamma frequency stimulation was previously shown to reduce Alzheimer's disease pathology and improve cognitive outcomes. This study aims to:

1. Determine whether non-invasive 40Hz sensory stimulation (ie, light, sound, tactile) can change brain activity.
2. Evaluate whether devices delivering non-invasive 40Hz sensory stimulation are safe in cognitively normal adults.
3. Determine whether non-invasive 40Hz sensory stimulation can change brain connectivity, neuropsychological measures, blood biomarkers, and the microbiome.

Inclusion Criteria:

• Have adequate visual and auditory acuity for visual and auditory stimulation to allow for neuropsychological testing.
• Be able to comply with neuropsychological testing and other study procedures in opinion of site PI.

Exclusion Criteria: Participants will be screened for the following exclusion criteria including if they

• History of seizure or medical diagnosis of epilepsy.
• Have MRI contraindications, such as presence of pacemakers, aneurysm clips, artificial heart valves, ear implants, metal fragments, or foreign objects in the eyes, skin, or body.
• Under the discretion of the site investigator, the site investigator feels the subject cannot complete sufficient key study procedures. Exceptions to these guidelines may be considered on a case-by-case basis at the discretion of the Project Director.