This study evaluates the effects of single-session Transcranial Direct Current Stimulation (tDCS) on fear reversal learning in patients with anxiety disorders. Participants will be randomized into four groups to receive either active stimulation targeting specific brain regions (right DLPFC or vmPFC), an active control stimulation, or sham stimulation. The main goal is to determine if modulating these brain areas can improve the ability to update safety and threat associations.

Anxiety disorders are characterized by deficits in fear regulation and cognitive flexibility, specifically the inability to inhibit fear responses when a threat becomes safe (fear reversal). Neurobiological models suggest this is linked to hyperactivity in the right dorsolateral prefrontal cortex (rDLPFC) and hypoactivity in the ventromedial prefrontal cortex (vmPFC).

This randomized, double-blind, sham-controlled study aims to verify if tDCS can improve fear reversal performance. The study involves 140 patients with anxiety disorders assigned to one of four arms:

Cathodal tDCS over the right DLPFC (inhibitory); Anodal tDCS over the vmPFC (excitatory); Sham tDCS (placebo); Anodal tDCS over the left DLPFC (active control). During the 25-minute stimulation session, participants will perform a computerized fear reversal task. Physiological data (Skin Conductance Response) and subjective anxiety ratings will be recorded simultaneously to assess the intervention's impact on cognitive and emotional regulation.

Inclusion Criteria:

Age between 18 and 60 years old. Right-handed. Meeting the DSM-5 diagnostic criteria for Gambling Disorder (GD). South Oaks Gambling Screen (SOGS) score ≥ 5. Normal or corrected-to-normal vision and hearing. Willingness to provide written informed consent and participate in the study.

Exclusion Criteria:

History of other severe psychiatric disorders (e.g., schizophrenia, bipolar disorder, severe depression) or neurological diseases (e.g., epilepsy, stroke, brain tumor).

History of substance abuse or dependence (excluding nicotine) in the past 6 months.

Current use of psychotropic medications that may affect cortical excitability (e.g., antidepressants, antipsychotics, anticonvulsants).

Presence of metallic implants in the head or neck area (e.g., cochlear implants, aneurysm clips) or cardiac pacemakers.

Skin lesions or sensitivity at the stimulation sites on the scalp. Pregnancy or lactation. Participation in other neuromodulation studies within the last 3 months.