Table 1 Inclusion and exclusion criteria for patients

• Fulfilment of ICD-10 diagnostic criteria for a primary depressive episode (i.e., not secondary to known organic or other psychiatric disorder)

• Referral to a treatment package for single-episode depression

• Age between 18 and 65 years

Exclusion criteria:

• Psychosis or psychotic symptoms

• History of severe head trauma involving hospitalization or unconsciousness for more than 5 min

• Known, substantial structural brain abnormalities

• Insufficient Danish language skills to complete questionnaires and cognitive testing

Additional exclusion criteria for subcohort I:

• Severe somatic disease

• Contraindications for MRI (e.g., metal implants, claustrophobia, or back problems)

Additional exclusion criteria for subcohort I:

• Use of psychotropic drugs

• Exposure to radioactivity > 10 mSv within the last year

• Pregnancy or breastfeeding