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Objectives: Encoding of fear stimuli is enhanced at heightened states of cardiovascular arousal (at cardiac systole). Oxytocin is a neuropeptide that selectively reduces fear memory through innervation of the amygdala. Here, we examined whether oxytocin could reduce learning and/or memory of fear stimuli for which feedback was provided at cardiac systole in a trial-and-error learning fMRI-paradigm. We further examined the modulatory effects of interoception (e.g. the detection of heartbeat signals) on fear learning and memory. Design: We used a double-blind, placebo-controlled within-subject design, testing for two levels of emotion (fear, neutral), cardiac timing (systole, diastole), and drug (oxytocin, placebo). Method: Participants (N = 30) inhaled 40 IU of oxytocin and placebo in two counterbalanced sessions prior to engaging in an fMRI trial-and-error learning task of fearful and neutral face-name pairs. Auditory feedback was delivered either at cardiac systole (on the heartbeat, when baroreceptors signal the contraction of the heart to the brain), or at diastole (between heartbeats during baroreceptor quiescence). Retrieval was tested after scanning. Results: A significant four-way interaction between drug, emotion, cardiac cycle and heart beat counting accuracy demonstrated that good heartbeat counters encoded fearful face-name pairs better during oxytocin than placebo when feedback was delivered at diastole relative to systole. No effects of drug were observed on intentional retrieval. However, post-hoc attractiveness ratings revealed a drug*emotion*cardiac timing interaction, showing that participants rated fearful faces as more attractive in the oxytocin relative to the placebo condition when they were initially reinforced at diastole relative to systole. FMRI data are currently being analysed. Conclusions: Oxytocin enhances the emotional sensitivity to socially relevant stimuli in individuals with higher interoceptive accuracy. Specifically, better encoding and higher attractiveness of fearful face-name pairs was observed with feedback delivered at diastole, suggesting that the anxiolytic effect of oxytocin might be the consequence of adequate feedback processing at lower levels of cardiovascular arousal. |
