A randomized, double-blind, placebo-controlled clinical trial will be conducted, using data from participants who met the diagnostic criteria for mild cognitive impairment and who participated in a primary clinical trial that investigated the effectiveness of treatment with tDCS for patients with this pathology. The study in question seeks to investigate differences in inflammatory profile and gene expression in peripheral blood of patients with MCI responders and non-responders to treatment with tDCS, where it is intended to establish a profile of biomarkers that can predict disease progression. Primary study participants will be assessed previously for eligibility, then randomized to receive sham or active tDCS. Then, they will be invited to participate in the prediction analysis study to identify the inflammatory profile and gene expression. The participants' venous blood will be collected during the clinical examination on the first day of treatment, before the first session of tDCS, with a new collection after the last session, that is, at the baseline and the end point of our study.

Healthy aging is associated with several changes in cortical function and these physiological differences are often interpreted as successful adaptation when cognitive performance is maintained; however, cognitive ability is not always preserved in aging. Mild cognitive impairment (MCI) is a cognitive decline syndrome commonly referred to as an intermediate phase between the expected cognitive decline of aging and pathological cognitive decline linked to dementia and generally does not interfere with daily activities. Pharmacological interventions have shown little positive impact and fail to demonstrate realizable benefits in mitigating cognitive decline in individuals with MCI and in preventing progression to Alzheimer's disease (AD). With this, there is a growing interest in exploring the benefits of non-pharmacological interventions such as Transcranial Direct Current Stimulation (tDCS), which can be a treatment modality to address the electrophysiological onset, deficits of metabolic and functional neural activation observed in MCI. Although tDCS has been studied in different dementias, there are still few studies investigating its use for MCI, with a significant lack of research in this area. Another issue to be explored is changes in the levels of biomarkers in body fluids and in specific brain regions of these patients, as they may allow the detection of cognitive changes even before the appearance of MCI. Different proteomic and genetic markers can result in a more accurate prediction of who will develop AD dementia in the future. The study in question seeks to investigate differences in the inflammatory profile and gene expression in the peripheral blood of patients with MCI responders and non-responders to treatment with tDCS, where it is intended to establish a profile of biomarkers that can predict the progression of the disease. Data from participants who met the diagnostic criteria for MCI and who participated in a clinical trial that investigated the effectiveness of treatment with tDCS for patients with this pathology will be used. Thus, it is necessary to mention the importance of early identification of the incipient forms of cognitive deficits, for the development of effective treatments. Several randomized controlled trials are underway to try to provide clinical evidence for the development of biomarkers that should provide the clinician with new tools to identify and treat MCI.

Inclusion Criteria:

• Individuals diagnosed with CCL will be included
• Individuals of both sexes, aged 65 and over
• Individuals who do not have diagnosis of dementia

Exclusion Criteria:

• Subjects with unstable medical conditions
• Patients with metallic implants and pacemakers
• Epileptic patients
• Individuals using drugs / alcohol
• Those who are under regular use of hypnotics and benzodiazepines up to two weeks before the start of the study
• Those who are using medication with cholinergic inhibitors for more than two months before this clinical trial

The study design in question involves patients with MCI, submitted to an intervention protocol, which includes: G1) active vs. G2) tDCS sham. These participants will be assessed previously for eligibility, then randomized to receive tDCS sham or active. All researchers responsible for the evaluation before and after the interventions will be blinded to the type of treatment the patient will receive (active stimulation or sham). The effectiveness of the masking mechanism will be assessed at the time of the last interview with patients when they will be asked about their opinion as to whether the electric current producing system was on or off.