Fig. 8: Study design, drug administration and blood sampling procedures.

(NB Nebuliser, IV Intravenous, PLC Placebo, pK Pharmacokinetics, RSF Resting-state BOLD-fMRI, VAS Visual Analog Scale). Upper panel—Drug allocation scheme: In each session, participants received treatment via all three administration routes, in one of two fixed sequences: either nebuliser/intravenous infusion/standard nasal spray, or standard nasal spray/intravenous infusion/nebuliser. In three out of four sessions only one route of administration contained the active drug; in the fourth session, all routes delivered placebo or saline. Unbeknown to the participants, the first treatment administration method in each session always contained placebo, while intranasal (spray or nebuliser) oxytocin was only delivered with the third treatment administration. The second administration was an infusion of either saline or oxytocin. Lower panel—Study protocol: After drug administration, participants were guided to the MRI scanner, where eight pulsed continuous arterial spin labelling scans (results reported elsewhere¹¹) and one resting-state BOLD-fMRI (RSF) were acquired, spanning 15–104 min after last drug administration offset. We assessed participants’ levels of alertness and excitement using visual analogue scales (VAS) at three different timepoints during the scanning session to evaluate subjective drug effects across time (results reported elsewhere¹¹). Intranasal administrations lasted for about 6 min, while the intravenous administration occurred at the highest rate of 1IU/min for 10 min. We collected plasma samples at baseline and at five timepoints post-dosing to measure changes in the concentration of oxytocin. The resting-state BOLD-fMRI scan used in this study was acquired between 57–65 min post last drug administration offset (the end of our second intranasal administration was considered time = 0). *Duration of treatment administration in minutes.