Sex difference in the relationship between salivary testosterone and inter-temporal choice.

Humans often prefer a small immediate reward to large reward in the future. This myopic tendency in inter-temporal choice is termed delay discounting, and has been the focus of intensive research in the past decades. Recent studies indicate that the neural regions underlying delay discounting are influenced by the gonadal steroids. However, the specific relationship between the testosterone levels and delay discounting is unclear at this point, especially in females. The present study investigated the relationship between salivary testosterone concentrations and discounting rates in delay- and probability-discounting tasks with healthy males and females. The results revealed a positive correlation between testosterone concentrations and delay-discounting rates in females and a negative correlation in males. Testosterone concentrations were unrelated to probability-discounting rates. Although causal effects of testosterone cannot be certain in this correlational study, if testosterone directly influenced this behavior, observed sex differences in delay discounting may be evidence of a curvilinear effect of testosterone. Alternatively, the findings may reflect inverse pattern of responsiveness to testosterone between male and female neural systems, or basic sex-difference in the neural mechanism underlying delay-discounting independent of testosterone itself.