Effects of hydrocortisone infusion on habituation to emotional faces in the human brain

Habituation to repeated images can be measured by repetition suppression, and emotional faces have been shown to influence repetition suppression differentially. It has been hypothesized that these differences in habituation are due to factors such as threat values and ambiguity of faces. Cortisol, a stress hormone, has been shown to influence response to emotional faces in other contexts and therefore may influence their repetition suppression. Three brain areas that may be relevant to repetition suppression, facial perception, and cortisol functions were examined: the fusiform gyrus, the hippocampus, and the parahippocampal gyrus. Subjects were divided into low (N=15) and high (N=18) dose groups and infused with placebo or hydrocortisone on two visits. During each visit, subjects viewed four kinds of emotional faces (fearful, happy, neutral, sad) as well as scrambled faces while placed in a functional magnetic resonance imaging (fMRI) scanner. Hydrocortisone in either dose was found to inhibit repetition suppression to all kinds of emotional faces in the fusiform gyrus. In the hippocampus, administration of hydrocortisone in low dose subjects shifted patterns of repetition suppression to favor happy faces, while low or high doses of hydrocortisone inhibited significant repetition suppression relative to placebo in the parahippocampal gyrus.