Oxytocin is a neuropeptide associated with prosocial behaviors, such as parent-child bonding, eye contact, and sexual activity. Intranasally-administered oxytocin has been widely used to study its effects on the brain using functional magnetic resonance imaging. Head motion is a significant confounding variable which was assessed as part of a double blind, placebo-controlled crossover study. Twenty-four mothers with drug addiction problems were initially recruited, along with 22 healthy control mothers, to test whether intranasal oxytocin enhances functional brain responses to images of their own versus unknown infant faces. Significant differences in head motion between oxytocin/placebo conditions and addiction/control groups were discovered. Administration of intranasal oxytocin was associated with more frequent counts of head motion exceeding 3 mm of framewise displacement, independent of group status (z=2.89, p=0.004). This effect was seen more strongly in the control group (z=2.30, p=0.02) than the addiction group (z=1.77, p=0.08). The addiction group was more likely to show increased head motion, independent of oxytocin or placebo condition (z=2.21, p=0.03). When examining the mean head motion across all time points, as opposed to the count of large movements, oxytocin's effect was limited to the addiction group (z=2.58, p=0.01), with a significant group by condition interaction effect observed. Intranasally-administered oxytocin may therefore have a confounding effect on functional MRI scanning results via its independent effect on head motion. These findings should be examined and replicated in other clinical populations.
Keywords: addiction; framewise displacement; functional MRI; head motion; oxytocin.