Behavioral and experimental paradigms
At each dosing visit, participants underwent physiological and brain monitoring during a baseline run featuring a short breathing challenge and for 30 min after saline or ketamine was injected. Physiological sensors (E4, Empatica, Boston, MA, USA and Lifesense, Nonin, Plymouth, MN, USA) measured respiration rate, SpODuring the baseline run, participants were verbally instructed to breathe normally for the first 8 min. Then they were asked to breathe rapidly and deeply until their EtCODuring the saline and ketamine administration, participants were partially reclined on a couch, supported by pillows. The pilot participant demonstrating the setup in Fig. 