The present research explored relationships between individual differences in motivational states (basal testosterone levels (study 1), implicit power motivation (study 2), implicit sexual motivation (study 3)) and both biology and behavior (brain responses to dominance signals (study 1), steroid hormone levels (study 2), and operant conditioning (study 3).

Testosterone is positively linked to dominance behavior in men. However, little is known about the moderating effects of testosterone in the human brain in the context of dominance. Study 1 used fMRI to measure amygdala BOLD response to interpersonal dominance signals of threat (anger faces) as a function of endogenous testosterone levels in 24 participants (10 men). Men's, but not women's, amygdala BOLD response to anger faces was negatively correlated with their endogenous testosterone levels.

Study 2 investigated basal and dynamic relationships between implicit power motivation (n Power) and both salivary estradiol and testosterone in women. During a laboratory dominance contest, participants competed in pairs on a cognitive task and contest outcome (win vs. loss) was experimentally varied. Estradiol and testosterone levels were determined in saliva samples collected at baseline and several times post-contest, including one day post-contest. n Power was positively associated with basal estradiol concentrations. Women's estradiol responses to a dominance contest were influenced by the interaction of n Power and contest outcome: Estradiol increased in power-motivated winners but decreased in power-motivated losers. Lastly, n Power and estradiol did not correlate with self-reported dominance and correlated negatively with self-reported aggression. Self-reported dominance and aggression did not predict estradiol changes as a function of contest outcome. Overall, n Power did not predict basal testosterone levels or testosterone changes as a function of dominance contest outcome.

In study 3, using a newly-created method, implicit sexual motivation themes were coded in participants' creative stories. To assess the predictive validity of coding implicit sexual motivation in creative stories, an operant conditioning paradigm was employed, which assessed the rewarding properties of visual sexual stimuli. Implicit sexual motivation was positively associated with implicit learning to achieve visual sexual reward, and this effect was particularly strong in men.