Older adults with Mild Cognitive Impairment (MCI) often show less brain activity in a specific range (8-13 Hz, known as alpha power) compared to healthy older adults. Those with lower alpha activity, especially in the front part of the brain, usually have problems with executive functions like planning and multitasking. Our research has shown that older adults with lower alpha power in these areas also struggle more with balance when they have to do two things at once (like standing and performing a cognitive task simultaneously).

The investigators believe that increasing alpha power in older adults with MCI could improve their balance and executive function, helping them stay independent longer. In early studies, the investigators found that using transcranial alternating current stimulation (tACS) at 10 Hz on the front part of the brain can boost alpha power and balance immediately after a single session in older adults with MCI. The effect was stronger in those whose natural brain activity was close to the 10 Hz stimulation.

Based on these findings, the investigators plan to conduct a pilot study with older adults aged 65-85 years with MCI. Participants will be randomly assigned to receive either real tACS or a sham (placebo) treatment. Our main hypothesis is that real tACS will improve balance when multitasking, and these improvements will last for 1 to 3 months after the treatment. The investigators also believe that tACS will enhance other aspects of executive function and mobility and that these improvements will be linked to increased alpha activity in the brain.

Through this study, we aim to gather strong evidence that tailored tACS is a promising treatment to improve cognitive and motor functions and overall brain activity in older adults with MCI.

Older adults with Mild Cognitive Impairment (MCI) exhibit reduced brain alpha power (i.e., activity fluctuations in the 8-13 Hz range) compared to healthy older adults, and older adults who exhibit lower alpha activity in the fronto-central areas tend to have impaired executive function. In addition, our group has demonstrated that older adults who exhibit lower fronto-central alpha power during dual-task standing (i.e., standing while performing an unrelated cognitive task) have worse standing balance performance. We, therefore, contend that strategies designed to increase alpha power in older adults with MCI hold promise to enhance dual-task balance and other measures of executive function, and ultimately help these vulnerable individuals maintain functional independence over time.

In our preliminary studies, we have demonstrated that a single exposure to transcranial alternating current stimulation (tACS) delivered at 10 Hz over the fronto-central regions of the brain increases alpha power and dual-task balance in older adults with MCI, when tested just after stimulation. We have also observed that in older adults with MCI, 10 Hz tACS appears to have a greater effect on alpha activity and dual-task balance in those individuals whose peak alpha frequency happens to be at or near the stimulation frequency (10 Hz).

Given the above evidence, we will conduct a pilot, double-blinded, parallel-arm, randomized controlled trial in ambulatory women and men aged 65-85 years with MCI. Our primary hypothesis is that compared to sham, tACS will improve dual-task balance when tested at the end of the intervention, and that such effects will persist at the 1- and 3-month follow-up. We further hypothesize that 1) tACS, compared to sham, will improve performance in other clinically-tractable measures of executive function and mobility, and 2) that tACS-induced improvements in dual-task balance will correlate with increased alpha brain activity. Through these efforts, we anticipate providing rigorous preliminary data that individually-tailored tACS is an effective therapeutic option capable of inducing sustained improvements in cognitive-motor functions, as well as underlying brain activity, in older adults with MCI.

Inclusion Criteria:

• Age 65+
• Who have been diagnosed with cognitive impairment (based in MoCA or TICS and Clinical Dementia Rating: CDR 0.5)
• Ability to stand and walk independently
• Willing and capable to give informed consent for the participation in the study after it has been thoroughly explained
• Cut off of MOCA score >18 will be applied
• Able and willing to comply with all study requirements informed consent form was signed
• Understanding of the ICF will be assessed by asking the participant to answer the following three questions: 1) What is the purpose of this study? 2) What are the risks of study involvement? 3) If you decide to participate, are you allowed to withdraw from the study at any time? Answers will be recorded by study personnel on the "Assessment of Protocol Understanding" form (see attached). Insufficient understanding will be defined by one or more incorrect answers, as determined at the discretion of the investigator.

Exclusion Criteria:

• Cut off of MOCA score <18 will be applied
• Major psychiatric co-morbidity including major depressive disorder, schizophrenia or psychosis
• Blindness or other disabilities that prevent task performance
• Self-reported history of stroke or neurodegenerative disorders other than MCI.
• Self-reported active cancer for which chemo-/radiation therapy is being received.
• Contraindications to tACS, as recorded on a standardized screening questionnaire, which include a reported seizure within the past two years, use of neuro-active drugs, self-reported presence of specific implanted medical devices (e.g., deep brain stimulator, medication infusion pump, cochlear implant, pacemaker, etc.), or the presence of any active dermatological condition, such as eczema, on the scalp.