Adding a low dose of ketamine to electroconvulsive therapy (ECT) for major depressive disorder does not improve overall response, remission, or relapse rates, but it does speed up the treatment's effects. Patients receiving 0.3 mg/kg ketamine before ECT required fewer sessions to achieve a response (median 4 vs. 7 sessions) and remission (median 8 vs. 9 sessions), and also reduced suicidal ideation more quickly (median 3 vs. 6 sessions). The findings suggest ketamine can accelerate the onset of ECT's antidepressant benefits without affecting long-term relapse.
Under LSD, people update their beliefs more quickly in response to surprising outcomes, and this behavioral marker of relaxed beliefs correlates with specific brain changes: lower alpha brainwave power and greater disintegration of the default mode network, particularly in the medial prefrontal cortex. These neural signatures support the REBUS model, which proposes that psychedelics relax the confidence in prior beliefs, making the brain more sensitive to prediction errors. The findings link a computational measure of surprise sensitivity to objective brain activity patterns, providing evidence for how psychedelics may alter belief updating and cognitive flexibility.