Experimental design & procedure
BLOOD
All eligible participants were randomly assigned to one of three treatment groups in a 1:1:1 ratio. Participants in the first group were pretreated with placebo and received a placebo infusion (placebo-placebo group, PP). Participants in the second group were pretreated with placebo and received a ketamine infusion (placebo-ketamine group, PK), and participants in the third group were pretreated with lamotrigine and received ketamine (lamotrigine-ketamine group, LK). All participants underwent two scanning sessions on two consecutive days. Before the first scanning session, participants were pretreated with an oral dose of 300 mg lamotrigine (LK) or matching placebo (PP, PK) 2 hours before the scanning procedures. During the first scanning session (acute), participants were intravenously administered ketamine or placebo (ketamine dosage: 0.12 ± 0.003 mg/kg during the first minute followed by a continuous infusion of approximately 0.31 mg/kg/h). Blood samples were taken 55 minutes after commencing ketamine infusion to determine ketamine plasma levels. Before the infusion started, all participants underwent a short resting state fMRI scan, that was repeated after the start of the infusion. Next, participants performed a picture viewing and an emotional working memory task (reported elsewhere; [