title: Oxytocin increases heart rate variability in humans at rest: implications for social approach-related motivation and capacity for social engagement.
abstract: BACKGROUND
  Oxytocin (OT) plays a key regulatory role in human social behaviour. While prior studies have examined the effects of OT on observable social behaviours, studies have seldom examined the effects of OT on psychophysiological markers such as heart rate variability (HRV), which provides an index of individual's motivation for social behaviour. Furthermore, no studies have examined the impact of OT on HRV under resting conditions, which provides an index of maximal capacity for social engagement.
  
  
  OBJECTIVE
  To examine the effects of OT on HRV measures in healthy male participants while at rest. OT was hypothesised to increase HRV, compared to placebo, and that the effects would be greatest for a non-linear measure of HRV (the detrended fluctuation scaling exponent).
  
  
  METHODS
  Twenty-one male participants were recruited for this study. Participants were non-smokers, not on any medications and reported no history of psychiatric illness, neurological disorder, or any other serious medical condition (e.g. diabetes, cardiovascular disease). The study employed a randomised, placebo-controlled, within-subject, crossover, experimental design.
  
  
  METHODS
  HRV was calculated from electrocardiography under a standardized, 10-minute, resting state condition.
  
  
  RESULTS
  As hypothesised, OT increased HRV and these effects were largest using the detrended fluctuation scaling exponent, a non-linear measure. These changes were observed in the absence of any change in state mood, as measured by the profile of mood states. Importantly, participants were unable to correctly guess which treatment they had been assigned at either of the two assessments.
  
  
  CONCLUSIONS
  Together with the broader literature on OT and HRV, findings suggest that acute administration of OT may facilitate a fundamental psychophysiological feature of social behaviour, increasing capacity for social engagement. Findings also suggest that HRV changes may provide a novel biomarker of response to OT nasal spray that can be incorporated into research on response to treatment.
authors.affiliation: School of Psychology, University of Sydney, Sydney, New South Wales, Australia. andrew.kemp@sydney.edu.au
authors.forename: Andrew H
authors.initials: AH
authors.lastname: Kemp
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Quintana
authors.forename: Rebecca-Lee
authors.initials: RL
authors.lastname: Kuhnert
authors.forename: Kristi
authors.initials: K
authors.lastname: Griffiths
authors.forename: Ian B
authors.initials: IB
authors.lastname: Hickie
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Guastella
mesh_terms: D000328:Adult; D018592:Cross-Over Studies; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D008297:Male; D009042:Motivation; D010121:Oxytocin / Q000494:pharmacology*; D012919:Social Behavior
chemical_list: D010121:Oxytocin