The purpose of this study is to locate clinical markers (for example, interviews, questionnaires, and computer tasks) and biological markers (for example, physiological, blood-based, or electroencephalography measurements) that predict response to cognitive behavioral therapy for depression.

Forty adult outpatients with major depressive disorder or persistent depressive disorder will receive up to 20 sessions of cognitive behavioral therapy for depression over 16 weeks. Participants will complete clinical measures (interviews, questionnaires, and computer-based tasks) and biological measures (blood tests, physiological measurements, electroencephalography ) before, during, and after treatment.

Inclusion Criteria:

• Clinical diagnosis of Major Depressive Disorder or Persistent Depressive Disorder according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition
• Must be fluent in English
• Must be capable to give informed consent

Exclusion Criteria:

• Lifetime diagnosis of Schizophrenia, Schizoaffective Disorder, Bipolar Disorder
• Current Alcohol or Drug Use Disorder (except tobacco or caffeine)
• Current psychotic symptoms
• Acute suicide risk
• Psychological treatment for depression initiated during the past three months
• Pharmacological treatment for depression initiated/changed during the past three months
• Previous non-response to two or more adequate trials of pharmacotherapy
• Current significant neurological disorder, head trauma, or unstable medical conditions.