Women who were already skeptical in their judgment of trustworthy faces did not change their judgment under the influence of testosterone (T). Rather, it was the 12 women who gave the highest ratings of trust under placebo who became significantly more skeptical after T treatment...Because endogenously produced T levels normally vary across time, these findings ... raise the question of whether fluctuating androgen secretion may normally modulate a person’s judgment of whether to trust people. There are circadian rhythms in T secretion, in both men and women, so is there also a circadian rhythm in how they judge trustworthiness in faces? There is also variation in circulating T in women across the menstrual cycle, with a modest peak in circulating T just a few days before ovulation, the very period during which copulation is most likely to result in pregnancy. What’s more, androgens such as T have been reported to boost women’s libido in several studies, including one study using the same sublingual dose of T, which increased sexual arousal. If androgens normally boost female libido, a peak in T before ovulation makes sense to evolutionary psychologists who might expect women to be most interested in sex when they are most fertile. What the present findings suggest is that women might also reach their peak in skepticism about the trustworthiness of other people, presumably including potential mates, at about this same point in the ovulatory cycle. Heightened skepticism about a potential mate’s trustworthiness also makes evolutionary sense in scenarios where a father’s ongoing support is crucial for survival of the infant.The review also speculates on where T may be acting in the brain:
...the amygdala has been implicated in many studies of social judgment, including making judgments about other people’s faces, and it is also a hotspot for neurons expressing the androgen receptors that T acts upon to regulate gene expression (14, 15). Thus, it is possible that T may alter social judgments by acting directly on the amygdala, perhaps, the authors suggest, by regulating the strength of signaling between the amygdala and other brain regions implicated in social evaluation, such as the orbitofrontal cortex.
Figure - Potential model for hormonal effects on interpersonal trust. The amygdala (center) is active during fearful responses or detecting threat in faces, and many neurons there possess androgen receptors, enabling them to respond to T. Bos et al. (4) suggest that T may reduce interpersonal trust by acting on vasopressinergic neurons in the amygdala to increase communication to brainstem systems that activate fearful responses, while reducing communication to orbitofrontal cortex. Oxytocin boosts interpersonal trust, perhaps by exerting opposing effects on these same systems.