Functional imaging and behavioural studies have shown that the neuropeptide oxytocin influences processing of emotional faces. However, it is not clear whether these effects reflect modulation at an early or late stage of affective processing. We investigated the effects of oxytocin administration on early and late visual evoked potentials (VEP) in response to faces with neutral, fearful and happy expressions. In addition, we measured multifocal VEP and its associated nonlinearities to ascertain whether any changes observed in electrophysiology were indicative of a generalised effect or of one tied strictly to emotional processing. In a randomized, double-blind, cross-over design, 27 healthy male participants self-administered a nasal spray of either oxytocin (24 IU) or placebo. At very early latencies (40-60ms), oxytocin reduced right-temporal responses to fearful faces (d = .51), and central responses to both fearful (d = .48) and neutral faces (d = .54). For left occipito-temporal electrode sites, oxytocin decreased P100 reactivity to fearful expressions (d = 0.72). Oxytocin also decreased the amplitudes of the vertex positive potential (140-180ms) and late positive potential (400-600ms), regardless of whether the faces had fearful, happy or neutral expressions. The mfVEP showed no signs of selective magno-or parvo-cellular peak modulation comparing OXT with placebo with either low or high contrast stimulation. These results suggest that at early stages of visual processing, nasal oxytocin modulates responses to facial emotions, whereas at later stages of visual processing, it appears to influence more general face processing mechanisms. In addition, the measurable effects of OXT appear to be not a result of generalized brain change, but systematically related to emotional processing.
Intranasal oxytocin modulates very early visual processing of emotional faces
