Clinical and Biological Markers of Response to Cognitive Behavioural Therapy for Depression

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.