Transcranial Alternating Current Stimulation (tACS) Combined With Cognitive Training in Alzheimer's Disease (AD_tACSrehab)

Participants will receive individualized computerized memory training for 8 weeks (2 sessions/week, 30 minutes/session) through synchronous telerehabilitation. The memory training will be individualized based on each participant's performance on the Face-Name Association Task (FNAT) and will use an errorless learning approach.

40 at-home sessions (5 days/week for 8 weeks), each consisting of the application of sham tACS applied over the precuneus for a duration of 60 minutes each. The electrode placement will be identical to that used for real stimulation. However, the electrical current will be automatically interrupted approximately 5 seconds after the start of stimulation, making it impossible for the participant to distinguish between sham and real stimulation.

40 at-home sessions (5 days/week for 8 weeks), each consisting of the application of tACS (real, 40 Hz) applied over the precuneus for a duration of 60 minutes each.

Participants will receive individualized computerized memory training for 8 weeks (2 sessions/week, 30 minutes/session) through synchronous telerehabilitation. The memory training will be individualized based on each participant's performance on the Face-Name Association Task (FNAT) and will use an errorless learning approach.

The global cognitive functioning will be assessed by Mini-Mental State Examination (MMSE); MMSE scores range from 0 to 30, with higher scores indicating a more preserved cognition.

Lexical-semantic access and executive functioning will be evaluated by Semantic Fluency Test. Participant is asked to generate as many words as possible from a given category within a limited time (60 seconds); higher scores indicate better performance.

Executive function will be assessed using the Trail Making Test, including Part A (visual attention and processing speed) and Part B (task switching and cognitive flexibility). Higher completion times reflect poorer performance.

Verbal memory will be assessed using the Rey Auditory Verbal Learning Test (RAVLT), including immediate recall (sum of trials), delayed recall after 15 minutes. Scores reflect the number of correctly recalled items.

The ADAS-Cog-13 consists of 13 tasks assessing cognitive domains including memory, language, praxis, orientation, and attention. Total scores range from 0 to 85, with higher scores indicating greater cognitive impairment.

The Face-Name Associative Memory Test is used to assess the participant's associative memory and is composed of encoding and retrieval phases, with higher scores indicating better function.

ADCS-ADL evaluates activities of daily living. The scores range from 0-78 with lower scores indicating more severe functional impairment.

Neuropsychiatric Inventory (NPI) is designed to be a structured clinical interview about neuropsychiatric and behavioral symptoms; the score ranges from 0 (no symptoms) to 144 (severe symptoms).

The Clinical Dementia Rating-Sum of Boxes (CDR-SB) assesses cognitive and functional impairment across six domains: memory, orientation, judgment and problem solving, community affairs, home and hobbies, and personal care. Total scores range from 0 to 18, with higher scores indicating greater cognitive and functional impairment.

The Clinical Dementia Rating Global Score (CDR-GS) assesses the overall severity of cognitive and functional impairment across six domains: memory, orientation, judgment and problem solving, community affairs, home and hobbies, and personal care. Global scores range from 0 to 3, with higher scores indicating greater impairment.

The Zarit Burden Interview (ZBI) assesses the perceived burden experienced by caregivers of individuals with dementia. It consists of 22 items rated on a 5-point scale. Total scores range from 0 to 88, with higher scores indicating greater caregiver burden.

By using transcranial magnetic stimulation (TMS), the investigators will evaluate the effects of gamma tACS on short latency afferent inhibition (SAI), which is a marker of cholinergic transmission. SAI is expressed as percent of the unconditioned motor evoked potential.

A venous blood draw will be performed at each timepoint. Samples will be processed for serum, plasma, and DNA extraction. Changes from baseline in biological marker concentrations, including plasma p-tau217, will be evaluated over time.

Demographic characteristics (age, gender, and level of education) will be evaluated as predictors of treatment efficacy and examined for associations with differential treatment response.

The Clinical Dementia Rating-Sum of Boxes (CDR-SB) will be used to assess disease severity at baseline and evaluated as a predictor of treatment efficacy and examined for associations with differential treatment response. The CDR-SB assesses cognitive and functional impairment across six domains: memory, orientation, judgment and problem solving, community affairs, home and hobbies, and personal care. Total scores range from 0 to 18, with higher scores indicating greater disease severity.

The Clinical Dementia Rating - Global Score (CDR-GS) will be used to assess disease severity at baseline and evaluated as a predictor of treatment efficacy and examined for associations with differential treatment response. The CDR-SB assesses cognitive and functional impairment across six domains: memory, orientation, judgment and problem solving, community affairs, home and hobbies, and personal care. Global scores range from 0 to 3, with higher scores indicating greater impairment.

Level of education and occupational attainment will be assessed at baseline as proxy measures of cognitive reserve and examined for associations with differential treatment response.

The plasma biomarker profile will be evaluated as a predictor of treatment efficacy and examined for associations with differential treatment response.