Changing Tactics? Optimizing ECT in Difficult-to-treat Depression

The goal of this randomized controlled trial is to address which treatment strategy (continue right unilateral (RUL) ECT or switch to bitemporal (BT) ECT speeds up recovery and has the least impact on memory function, in case of early non-response during an acute course of ECT for difficult-to-treat depression. The main questions it aims to answer are: * Assess the antidepressant efficacy and cognitive impact of the continuation of an ongoing treatment with RUL ECT compared to switching the treatment technique to BT ECT, in patients failing to show an early response to an acute course of ECT for major depression; * Assess group and subject-specific trajectories of depressive symptom severity and neurocognitive performance during the acute ECT course and up to 3 months post-treatment. Participants treated with ECT for depression, showing no 'response' (≥50 percent decrease in depressive symptom severity compared to baseline) after 4 treatment sessions, will be randomized to either switch to BT ECT or continue with RUL ECT. Mood and neurocognitive assessments will be performed at baseline, after 4 ECT sessions (before randomization), after 8 ECT sessions, at the end of the acute course and 3 month after the acute course.