Decision-making is a complex cognitive function that has been the subject of extensive scientific research in the fields of cognitive and computational neuroscience. It relies on a cerebral network that encompasses cortico-subcortical pathways. The orbitofrontal cortex (OFC) plays a significant role in decision-making by assigning values to guide choices. Risky decision-making is observed in several psychiatric pathologies, including depression and bipolar disorder, and it may constitute an endophenotype of suicide. In the project presented here, we propose to use transcranial direct current stimulation (tDCS) to target decision-making in patients suffering from mood disorders.

The primary objective is to assess the ability of tDCS applied to the orbitofrontal cortex to improve decision-making, as measured by the Iowa Gambling Task, compared to a placebo stimulation in patients suffering from mood disorders.

The secondary objectives are as follows:

• To assess whether the evolution of decision-making under tDCS stimulation is independent of emotional changes (sadness, anxiety).
• To evaluate if tDCS stimulation of the orbitofrontal cortex improves motor inhibition, assessed using the D2-test, compared to a placebo stimulation.
• To determine if tDCS stimulation of the orbitofrontal cortex reduces sensitivity to interference, assessed with the Stroop test, compared to a placebo stimulation.
• To evaluate if tDCS stimulation of the orbitofrontal cortex enhances cognitive inhibition, measured by the Go-no go test, compared to a placebo stimulation.

This is a prospective monocentric interventional randomised controlled trial with two parallel groups, one receiving active treatment with tDCS and the other receiving a placebo (sham tDCS). The randomization will be performed in variable-sized blocks and will be stratified based on the current mood state (current depression versus current euthymia). It is a single-blind study where the patients and the outcome assessor are blinded to the type of treatment received.

Recruitment will take place at "la Clinique des Maladies Mentales et de l'Encéphale de l'Hôpital Sainte-Anne" and will involve hospitalized patients as well as those in outpatient care. Pre-inclusion visit involve patient selection, verification of inclusion criteria, and the provision of information documents. Inclusion visit occur at least one day later, lasting for three hours. It involves the verification of both inclusion and exclusion criteria, obtaining informed consent, randomization, collecting socio-medical-demographic data, and conducting psychometric and neuropsychological assessments. Stimulation visit, also scheduled at least one day later and lasting three hours, encompass the measurement of primary and secondary evaluation criteria immediately before and after tDCS stimulation. A group guessing test concludes the study.

An interim analysis is planned, and an Independent Data Monitoring Committee (IDMC) will be established to oversee the data.

Inclusion Criteria:

• Patients under consideration should either be receiving outpatient or inpatient care.
• Patients must be between the ages of 18 and 65, inclusive.
• According to DSM-5 criteria, patients should be diagnosed with either unipolar or bipolar depressive disorder. This includes individuals currently experiencing a characterized depressive episode with mild to moderate intensity, those in partial remission, or those in full remission.
• Patients must have provided informed consent.
• Patients should be enrolled in a social security plan.

Exclusion Criteria:

• Patient unwilling to participate in the research.
• Non-French-speaking individuals.
• Individuals deprived of liberty by judicial or administrative decision, such as those under guardianship or curatorship or involuntarily hospitalized.
• Pregnant or breastfeeding women.
• Current hypomanic or manic episode as per DSM-5 criteria due to motor agitation issues.
• Ongoing electroconvulsive therapy (ECT) treatment or within the last 6 months.
• Patients with active implantable medical devices.
• Epilepsy.

The patients and the outcome assessor are blinded to the type of treatment received.

Each patient, at the end of the study, will be asked to guess whether the treatment received was active or sham.