Between recovery and relapse Examining partial remission and cognitive functioning in major depressive disorder

Although effective treatments are available, approximately one-third of individuals continue to experience clinically relevant residual symptoms after a depressive episode. This state, referred to as partial remission of major depressive disorder (MDD), is distressing and associated with a range of adverse outcomes, including increased risk of relapse. Despite its relevance, partial remission remains relatively neglected in both research and clinical practice. This thesis examined partial remission as a distinct and important phase of MDD, with a particular focus on optimizing treatment and understanding the role of cognitive functioning. First, the available evidence on treatment strategies for partial remission was systematically evaluated. A meta-analysis and an individual participant data meta-analysis demonstrated that psychological interventions reduce residual depressive symptoms and lower relapse risk, with benefits generalizing across a range of patient characteristics. Next, the role of cognitive functioning in the course of depression and its potential as a treatment target was investigated. A 20-year longitudinal study found no evidence for bidirectional associations between cognitive functioning and the course of depression, showing only limited cognitive change over time and no support for progressive cognitive scarring or state-related cognitive decline. Finally, a randomized controlled trial demonstrated that adding neurocognitive remediation therapy to preventive cognitive therapy did not improve cognitive functioning, residual symptoms, or relapse prevention. Overall, this thesis demonstrates that improving outcomes in partial remission requires implementation of effective psychological interventions that are already available. At the same time, the findings challenge the assumption that cognitive functioning should be routinely targeted to improve the course of depression.