The goal is to determine whether three months of at least three times / week of sensory flicker stimulation improves cognition, mobility, and affect in healthy older adults and older adults with and without Subjective Cognitive Decline (SCD). Investigators will also determine whether the intervention slows cortical thinning and declines in brain functional network segregation and changes in blood biomarkers of Alzheimer's Disease (AD).

Inclusion Criteria:

• Community dwelling men and women 65-89 years old
• Ability to walk unassisted for 10 min
• English speaking

Additional Inclusion Criteria for SCD:

• No evidence of dementia or MCI based on cognitive screening (i.e., Montreal Cognitive Assessment (MoCA) score within normal limits for age, education, and sex using the NACC Uniform Data Set (UDS) norms8
• Global Clinic Dementia Rating (CDR) score must be 0 or 0.531
• Subjective report of cognitive complaints with scores >20 on the Cognitive Change Index (CCI-20), a validated scale of subjective cognitive decline6; this scale consists of 20 items that are rated on a 5-point Likert scale, where 1= "Normal: No change compared to 5 years ago", 3= "Mild Problem: Some change compared to 5 years ago) and 5="Severe Problem: Much worse compared to 5 years ago"
• Family history of dementia/probable AD in first degree relative (parents, children, siblings)
• Normal functional behavior in terms of daily activities, based on the Functional Activities Scale32
• In line with recommendations of the SCD task force33 an informant must be available for two reasons: a) to provide information about the participant's cognition using the informant version of the CDR and CCI-20, and b) to corroborate normal IADL's on the Functional Activity Questionnaire32 (informant data will be collected via a phone call and linked by code with the participant data).

Exclusion Criteria:

• If participants score less than 21 on the Telephone Interview for Cognitive Status (TICS)
• Significant medical event requiring hospitalization in the past 6 months that has the potential to contaminate data being collected (fracture, hospitalization etc.)
• Severe visual impairment or corrected visual acuity less than 20/40, which would preclude completion of assessments
• Inability to undergo MRI brain imaging due to claustrophobia or implants such as pacemakers, heart valves, brain aneurysm clips, orthodontics, certain non-removable body jewelry, or shrapnel containing ferromagnetic metal
• History of severe stroke
• Any major ADL disability (unable to feed, dress, bath, use the toilet, or transfer)
• Report of lower extremity pain due to osteoarthritis that significantly limits mobility
• Diagnosis or treatment for rheumatoid arthritis
• Known neuromuscular disorder or overt neurological disease (e.g. Multiple Sclerosis, Rhabdomyolysis, Myasthenia Gravis, Ataxia, Apraxia, post-polio syndrome, mitochondrial myopathy, Parkinson's Disease, ALS etc.)
• Unable to communicate because of severe hearing loss or speech disorder
• Planned surgical procedure or hospitalization in the next 4 months (joint replacement, coronary artery bypass graft, etc.)
• Severe pulmonary disease, requiring the use of supplemental oxygen
• Terminal illness, as determined by a physician
• Severe cardiac disease, including NYHA Class III or IV congestive heart failure, clinically significant aortic stenosis, recent history of cardiac arrest, use of a cardiac defibrillator, or uncontrolled angina
• Use of walker or wheelchair