Ovarian cycle effects on immediate reward selection bias in humans: a role for estradiol.

A variety of evidence suggests that, among humans, the individual tendency to choose immediate rewards ("Now") over larger, delayed rewards ("Later"), or Now bias, varies with frontal dopamine (DA) levels. As cyclic elevations in estradiol (E+) modulate other frontal DA-dependent behaviors, we tested ovarian cycle effects on Now bias, and whether any such effects are E+ mediated. To do so, we quantified Now/Later choice behavior in naturally cycling adult females (n = 87; ages 18-40 years) during both the menstrual phase (MP; cycle day 1-2; low E+), and the follicular phase (FP; cycle day 11-12; high E+).