This study aims to investigate whether the combination of transcranial Direct Current Stimulation (tDCS) and cognitive-behavioral therapy (CBT) is more effective for treating repetitive negative thinking (RNT) in patients with the symptom of high rumination. High ruminators will be included (Group1, active tDCS-CBT group; Group2, sham tDCS-CBT group). All patients will receive active or sham tDCS.

A psychoeducational CBT-based group intervention called 'Drop It' specifically for the treatment of repetitive negative thinking (RNT), which has been proved to be effective in reducing RNT. tDCS is one of the emerging non-invasive brain stimulations techniques that can also be used to alter RNT. Our aim is to explore the therapeutic effect of this combination.

The study consists of 2 stages. In the first stage the participants will come to the university hospital for 7 weeks CBT sessions (the Drop It intervention), with one session per week. After each CBT session, both groups will receive sham or active tDCS. Stimulation will be applied for 30 min after the CBT session.

In the second stage, after the 7th weekly CBT session, participants will take the devices home to apply daily home-based tDCS stimulations for 4 weeks. After 4 weeks, participants will return to the university hospital for the final CBT session.

Neuroimaging: Electroencephalogram (EEG) and functional Near-Infrared Spectroscopy (fNIRS) scan will be used to measure electrical activity and cortical hemodynamic activity in the brain. Both of these methods are non-invasive neuroimaging techniques which are done by placing electrodes on the scalp to pick up the signals produced by the brain.

EEG and fNIRS scans will be performed at baseline and after 3 months therapy.

To examine the effect of the worry course combined with tDCS on thinking and acting, the investigators will ask the participants to complete various questionnaires that assess the nature and extent of worry, the presence of depressive complaints, the presence of anxiety problems and the extent of quality of life as experienced by the participants. Participants will also be evaluated by a psychiatrist from the service. This evaluation will take place at baseline, just after the end of the Drop It course and after a 3-month follow-up. Two questionnaires will also be used after each session to measure the state rumination following the combination therapy of CBT and tDCS.

Inclusion Criteria:

• Generalized anxiety disorder (GAD)
• Depressive disorder

Exclusion Criteria:

• other psychiatric pathology than GAD or depression screened by senior psychiatrist by means of the Mini-International Neuropsychiatric Interview (MINI) and psychiatric anamnesis
• Abuse of alcohol, drugs or medication other than prescribed by general practitioner or psychiatrist
• no consent to participate in measurement (questionnaire, fNIRS or EEG)
• Insufficient knowledge of the current language (Dutch)
• Acute or chronic suicidality
• Acute psychosis or manic depressive disorder
• Inability to commit to 8 sessions of Cognitive-Behavioral Therapy (CBT) or receive 4 weeks of transcranial Direct Current Stimulation (tDCS).

Participants will be allocated into two groups randomly (using a code). The psychotherapist, the study managers and the patients will not be aware of treatment allocation.