This clinical trial aims to determine if Transcranial electrical stimulation by direct current (tDCS) and transauricular Vagus Nerve Stimulation (tVNS) treatments are effective in reducing stress symptoms, distress and improving sleep quality in adults. The main questions it aims to answer are:

• Determine if tDCS effectively reduces the intensity of stress symptoms in adults.
• Determine if tDCS is effective in reducing levels of distress in adults.
• Determine if tDCS is effective in improving sleep quality.
• Determine if tVNS is effective in reducing the intensity of stress symptoms in adults.
• Determine if tVNS is effective in reducing levels of distress in adults.
• Determine if tVNS is effective in improving sleep quality.

Stress is a disorder that significantly impacts the lives of affected individuals. Pharmacological treatment has limitations, justifying the search for non-pharmacological interventions. tDCS is a technique that modulates neuronal excitability and has shown promising results in various disorders.

Psychological stress affects a wide range of brain functions and poses risks for many mental disorders. However, effective therapies to alleviate or reverse its deleterious effects are lacking. Given that the pathophysiology of stress involves brain regions such as the prefrontal cortex, central amygdaloid nucleus, amygdala, medial amygdaloid nucleus, and ventral hippocampus, thus making the condition complex, there is a need for studies evaluating the effects of this intervention. We aim to contribute to the understanding of the role of tDCS and tVNS in managing stress.

Before participating in this research, volunteers will receive all information related to the study's objectives and methodological procedures. After agreeing to participate, they will sign the Informed Consent Form.

Study Location Patients will be selected following an evaluation based on inclusion and exclusion criteria and referred to the Clinic School of the Federal University of Alfenas (MG/Brazil), at the Laboratory of Neuroscience, Neuromodulation, and Pain Study (LANNED), located in the city of Alfenas, Minas Gerais, and at the Neuromodulation and Pain Unit (UNP) by the Egas Moniz Center for Interdisciplinary Research (CiiEM) of the Egas Moniz School of Health and Science, in the municipality of Almada, Setúbal - Portugal.

The design of the double-blind randomized clinical trial will be conducted, ensuring that participants are randomly assigned to experimental and sham groups and that the researcher applying the technique and the participants will not be aware of the allocation. The protocol will consist of 5 consecutive sessions of 20 minutes each. Data related to the anamnesis, ISSL, PSS-10, and PSQI will be evaluated at five different time points (Figure 1): before the intervention (T0), immediately after the end of the intervention (T1), and four weeks (T2) after the intervention ends (follow-up), following the CONSORT/2010 recommendations.

Inclusion Criteria:

• individuals previously diagnosed with stress.
• Obtain a score above 4 on the Lipp Adult Stress Symptom Inventory (ISSL);
• Must be able to read and understand the purpose of the research and respond to the assessment instruments.
• Must acknowledge and agree with the informed consent form.

Exclusion Criteria:

• smokers;
• be pregnant;
• initiation and/or change in psychotropic drug dosage in the last three months;
• use of anxiolytics or antidepressants;
• substance dependence;
• history of dizziness or seizures;
• signs of severity and/or indications for hospitalization or psychotherapy;
• diagnosis of depression; diagnosis of anxiety; bipolar mood disorder with depressive, manic, or hypomanic symptoms in the past year;
• schizophrenia or other psychotic disorders;
• autism;
• diagnosis of epilepsy or use of anticonvulsants;
• contraindications for tDCS (metal implants, tumor, previous brain surgery, significant cranioencephalic anatomical alterations);
• contraindications for non-invasive vagus nerve stimulation (cochlear implant, ear plastic surgery, ear malformation);
• adverse effects detected in the group treated with tDCS and tVNS, including itching, tingling, headache, burning sensation, and discomfort.