Chatbot Intervention Effects on Belief Updating in Anhedonia

Inclusion Criteria: * 18-40 years * Right-handed * Normal or corrected normal visual acuity * Participants must show elevated anhedonia and depressive symptoms at screening, defined as a total score of 23.5 or higher on the Snaith-Hamilton Pleasure Scale and a score of 14 or higher on the Beck Depression Inventory Exclusion Criteria: * History of major central nervous system disorders, such as epilepsy, traumatic brain injury, stroke, or brain tumors. * History of severe mental illness, including schizophrenia spectrum disorders, bipolar disorder, or other psychotic disorders. * History of substance or alcohol use disorder or substance or alcohol misuse within the past 12 months that may affect study participation or outcome assessment. * Individuals currently at high risk of suicide, severe self-harm, or experiencing an acute psychiatric crisis. * Individuals who are currently using psychiatric medications or have undergone psychotherapy within the past 4 weeks that may significantly affect mood, motivation, or reward processing. * Severe vision or hearing impairments that cannot be corrected and would interfere with task performance. * Contraindications to MRI scanning, including metallic implants, pacemakers, severe claustrophobia, or other conditions incompatible with MRI. * Pregnancy or breastfeeding.