An investigation into the role of oxytocin in emotion after injury or trauma

Oxytocin (24 International Units) administered via nasal spray. Participants will self administer the intranasal spray under verbal instructions from the researcher. Participants will be instructed to keep the bottle in an upright position during the puffing. Before puffing commences, four pre-puffs will squirted from the spray bottle by the researcher to ensure normal distribution of each spray before use. The order of administration was always as follow: insert spray-head, exhale, puff, inhale nasally. Administration will alternate between the nostrils after each spray, with 45-second break between each administration, until 3 puffs (4 IU each) per nostril is reached (total dose 24 IU). Participants were allowed to blow their noses before puffing commenced and will be asked to avoid this until the end of the testing sessions. They will be allowed to dab off any leaking fluid from their noses with a tissue. A stopwatch will be used to time the 45-second breaks, and again after the last puff to keep time until the expected peak levels of oxytocin within the central nervous system (approximately 45 minutes after the administration of the last spray). As this is a randomised crossover trial, participants will receive the oxytocin nasal spray in one session, and the placebo spray in the other. The two sessions are separated by a minimum of 7 days. Following the administration of the sprays and waiting for the sprays to become active within the central nervous system, the researcher will guide participants through a series of experimental tasks, which are described below. Task 1: Oxytocin, heart rate variability, and stress When the participant is comfortable, heart rate will be recorded while participants are prompted to inhale and exhale at regular intervals of 15 cycles per minute for two minutes. Spectral analysis with Fast Fourier Transformation will compute variability in low and high frequency heart periods (HRV). Respiratory sinus arrhythmia (RSA) will be analysed with the peak-to-valley method, calculating the mean difference between the shortest heart R-R period during inspiration and the longest R-R period during expiration. Following the paced breathing task, participants will be asked to complete a cognitive stressor task, the Serial Sevens (SS) task to induce a state of stress. Participants will be instructed to count backwards by sevens (e.g., 1,000, 993, 986, 979 etc.) while the experimenter pressures them to “hurry up” and “go faster” over a period of two minutes. Task 2: Film stimuli task Participants will then be asked to view and rate the emotional film clips. This task will take about 20 minutes. After the emotional film protocol, participants will be given a post-stimulus questionnaire, where they will be asked to rate a series of questions on a 5-point likert scale from 1 (Strongly disagree) to 5 (Strongly Agree). Each session will present 14 different clips, which will be matched on emotional stimulus type (neutral, positive, negative, fear) and valence and arousal.