The General Objective of the study is to evaluate the short- and long-term efficacy of combining transcranial Direct Current Stimulation (tDCS) and cognitive training (CT) in patients with mild cognitive impairment due to Alzheimer's disease. A randomized, single-blind, placebo-controlled design will be applied. An inter-subject design with two groups will be used: a. Active tDCS + concurrent CT and b. Sham tDCS + concurrent CT. Evaluations will be taken at pre-test, post-test, and follow-up one month later. The hypothesis comparing active and sham tDCS with concurrent CT is that, although both groups should improve due to concurrent CT, it is expected that the active tDCS group will show significantly greater improvements in post-treatment. Additionally, these improvements should be maintained in the long-term follow-up in the active tDCS group, while in the sham tDCS group, a partial loss of gains is expected at follow-up.

Transcranial Direct Current Stimulation (tDCS): HDC stimulators (Newronika TM, Milan, Italy) will be used. For active stimulation, the current intensity will be constant at 2 mA, with a stimulation time of 20 minutes daily for 10 days, and an initial and final ramp of 30 seconds. For the placebo group, current will only be applied during the initial and final ramps to generate the sensation of active stimulation. A neoprene cap with carbon rubber electrodes and sponges soaked in saline solution (5 x 5 cm) will be used. The anode will be placed over the left dorsolateral prefrontal cortex (DLPFC), and the cathode over the right supraorbital area (rSO).

Cognitive Training (CT): The CT will consist of 10 sessions of 50 minutes each, based on tasks involving executive functions and memory, including categorization, answering questions, short stories, problem-solving, recalling autobiographical moments, planning simple tasks, and schedule analysis.

As a preliminary step to this study, it should be noted that contact with patients will be obtained from the Neurology service at the Consorcio Hospital General Universitario. Before starting the research and to obtain subject participation, the service will inform potential participants about the possibility of being included in a study related to electrical stimulation, noting that they will have to receive intervention through transcranial Direct Current Stimulation (tDCS) and Cognitive Training (CT) for ten days. Once an initial commitment to possible participation is obtained from the patients, they will be informed that they will receive a phone call from the research team at the University of Valencia to schedule an in-person appointment where they will be provided with detailed information.

During this first appointment, held at the assigned health center or specialty center, the intervention procedure will be explained in more detail, and informed consent will be obtained from those subjects who decide to participate. It is important to highlight that the information regarding the procedure will emphasize aspects related to the safety and tolerability of the treatment, adherence to it, and the ease of application given its home-based nature.

From this point, the clinical interview will aim to assess the general health status and assess compliance with inclusion and exclusion criteria.; a neuropsychological evaluation will also be performed, although participants will be given the option to undergo this first evaluation during a second appointment. It should be noted that the total duration of the evaluation for participants in the early dementia group may be approximately 50 minutes.

Once the baseline evaluation is available, a coordinated schedule with the participants will be set to establish the start of the treatment and its continuity for the assigned duration; this aspect is crucial as a commitment to continuity from the participants is necessary. To facilitate this, a flexible start date will be provided to avoid any planned interruptions during the process. Additionally, given its home-based nature, the necessary information for home visits will be obtained, and an approximate time for the intervention will be established to ensure consistency. For this process, a psychologist hired for this purpose will visit the homes of the participants to carry out the stimulation. The psychologist administering the intervention was not blinded to group allocation, whereas participants and outcome assessors remained blinded.

The main critical point of this project is believed to be treatment adherence. Multiple sessions require subjects to repeatedly travel to the treatment location, posing a significant and often insurmountable burden for patients and their caregivers, along with substantial time and cost for service providers, especially as sample size increases. This difficulty often results in a high dropout rate. Providing tDCS and CT treatment at home, as proposed in this project, can reduce the burden on patients and their families by eliminating the need to travel to medical or research facilities for each treatment session, promoting adherence and compliance with the treatment. Therefore, implementing the outlined procedure in this research appears necessary not only to evaluate clinical efficacy but also to ensure the correct execution of stimulations and prevent dropouts.

Additionally, it is believed that one of the strengths and a key contingency strategy for addressing the mentioned critical point is the team's ability to adapt to contact with this type of patient and their caregivers. In this regard, it is crucial to implement an innovative paradigm, already applied in previous projects and leading global healthcare transformation, known as Patient Centricity (patient-centered care). Patient participation and care are essential aspects of research and procedural development, as well as disease management. Health outcomes depend on patient involvement, and there is a clear need to partner with them in the research, development, implementation, and advancement of health procedures to achieve better results. Creating a patient-centered solution involves obtaining input from patients and their caregivers, as is the case with this project, and making decisions based on their needs and perspectives. Humanizing science contributes to better acceptance, improving patient relationships and safety, and helping to prevent errors.

Considering the study groups, 3 repeated measures (pre, post, and follow-up), a statistical power of 95%, and a 95% confidence interval with an estimated effect size of η² = 0.16, it is estimated that an N = 30 participants would be needed, which means 15 subjects per group. However, due to recruitment constraints, the final sample consisted of 22 participants, which may have reduced the statistical power of the study.

The data will be analyzed using linear mixed-effects models to account for the repeated measures structure of the data, with group (active vs. sham) as a between-subjects factor and time (pre, post, follow-up) as a within-subjects factor. The efficacy of tDCS will be assessed by examining the interaction between group and time.

Participants were eligible if they met criteria for mild cognitive impairment due to Alzheimer's disease (MCI due to AD), defined as a score ≥ 23 on the Mini-Mental State Examination (MMSE) and classification at Stage 3 on the Global Deterioration Scale (GDS).

Exclusion criteria included contraindications to transcranial direct current stimulation (tDCS), such as intracranial metal implants or intracranial hypertension, as well as the presence of significant cerebrovascular disease or severe psychiatric symptoms.

The main reason for not sharing the individual participant data (IPD) description plan is to preserve the confidentiality and privacy of clinical trial participants. The protection of participants' personal and medical information is considered a top priority in this study.

from enrollment until the end of the follow up, up to 2 months

Non- Specified

Participants and outcome assessors were blinded to group allocation. The psychologist administering the intervention was not blinded.