The effect of oxytocin on autonomic flexibility following a traumatic experience: A pilot study

Abstract

A traumatic experience can lead to poor emotion-regulation and hyperarousal. The hormone oxytocin appears to normalise emotional reactivity in persons with symptoms of psychopathology, and modulates the salience of social and emotional cues, leading to context-dependent changes in adaptive responding. The mechanistic effect of oxytocin following trauma remains unknown. This small pilot study employed a double-blinded randomised crossover design to investigate the effect of oxytocin on autonomic-flexibility (high-frequency heart rate variability; HF-HRV) following a traumatic experience. This study also sought to determine whether effects were attributable to PTSD hyperarousal symptoms (Posttraumatic Checklist; PCL-5). Eleven participants (6 females, mean age 28) who experienced trauma (6-24 months prior) were asked to self-administer oxytocin (24IU) or placebo via nasal-spray, across two sessions at least one week apart. Each session included two tasks: a paced-breathing task (rest), which instructs participants to inhale and exhale at regular intervals, and the serial-sevens task (stress), which induces mild cognitive and physiological stress. HF-HRV was recorded from a 5-lead ECG system. Following oxytocin administration, HF-HRV decreased during the paced-breathing task (p = 0.03) and serial-sevens task (p = 0.056) compared to placebo. This effect ceased when covarying for PTSD hyperarousal symptoms during the serial-sevens task (p = 0.08). These findings suggest that oxytocin increased the salience of cognitive stress, which was specifically attributable to hyperarousal symptoms. As an index of parasympathetic activity, lower HF-HRV suggests that oxytocin reduced the engagement of the parasympathetic nervous system (PNS). While caution is advised, given the small sample size, it appears that oxytocin may increase the perceived salience of, and attention to, stressors thereby exacerbating physiological stress states (i.e., decreasing the capacity of the PNS to dampen arousal).