Eighty-eight participants aged between 18-70 years with major depressive disorder who start electroconvulsive treatment (ECT) will be included in this randomized controlled trial (RCT). Following (partial) response to ECT treatment (at least a 25% reduction of clinical symptoms), participants will be randomly assigned to a computer based CCT or active placebo control. A first aim of this RCT is to assess the effects of CCT compared to an active placebo condition on depression symptomatology, cognitive complaints, and quality of life. Secondly, participants will be monitored every two weeks for a period of six months following CCT/active placebo, allowing the detection of potential relapse of depression. Thirdly, the investigators will assess participant evaluation of the addition of cognitive remediation to ECT using qualitative interview methods (satisfaction, acceptability and appropriateness). Finally, in order to further advance our understanding of the mechanisms underlying effects of CCT, exploratory analyses may be conducted using facial video footage collected during the CCT/active control phase of the study.