Endocrine correlates of implicit motives
A great deal of research at the HuMAN Lab is dedicated to exploring the relationship between implicit motives and hormonal response systems. The HuMAN Lab specializes in the assessment of steroid hormones in human saliva, a non-invasive, stress-free method of measuring endocrine processes. Past and current research is focused on three different lines of inquiry:
In humans and animals, the gonadal steroid hormone testosterone drives, and is driven by, an individual's social rank and decreases the threshold for dominant and aggressive behavior, particularly if status is challenged. Studies conducted at the HuMAN Lab demonstrate that in men, the power motive is positively associated with baseline testosterone levels, predicts increases in testosterone after mere anticipation of dominance (Schultheiss, Campbell, & McClelland, 1999) and also in response to beating another person during a contest based on a speed-based task (Schultheiss & Rohde,
2002; Schultheiss, Wirth, Torges, Pang, Villacorta, & Welsh, 2005). In contrast, after a defeat, the power motive predicts either stagnating (Schultheiss & Rohde,
2002) or declining testosterone levels (Schultheiss, Wirth,
et al., 2005) in men.
In women, power motivation appears to be linked to estradiol, testosterone's close steroid cousin. Female power motivation levels are positively associated with estradiol (particularly in single women and women not taking oral contraceptives) and show a similar functional relationship to dominance outcomes as male power motivation levels do with testosterone: power-motivated women respond with lasting estradiol increases to winning a contest against another woman and with decreases to a defeat (Stanton & Schultheiss, 2007, 2009).
Thus, the HuMAN Lab has obtained evidence that power motivation is consistently related to baseline levels and situation-induced changes of gonadal steroid hormones in both genders (see also Schultheiss
et al., 1999; Schultheiss, Dargel, & Rohde, 2003 b; Schultheiss, Wirth et al., 2005). Taken together, these findings suggest that high testosterone (in men) and estradiol (in women) are a marker of a strong implicit power motive and that the power motive determines how strongly individuals' gonadal steroids responds to the arousal, satisfaction, or frustration of dominance-related concerns, with the generally stronger hormone responses in high-power individuals probably serving to increase (or decrease, depending on the outcome of a contest) the likelihood of future dominant and aggressive behavior (see Schultheiss, 2007, and Stanton & Schultheiss, 2009, for summaries).
Research conducted at the HuMAN Lab and associated labs has also uncovered a link between implicit affiliation motivation and progesterone, whose physiological effects (e.g., in the induction and maintenance of pregnancy in women and the suppression of testicular function in men) are well described, but whose psychological functions have so far remained much more elusive. Oral contraceptive use is associated with increased levels of implicit affiliation motivation, and among women not using the pill, higher levels of naturally occurring progesterone are associated with stronger affiliation motivation (Schultheiss, Dargel, & Rohde, 2003). Moreover, romantic movies that arouse the implicit need to affiliate also lead to increases in progesterone levels for men and women; in contrast, neutral movies or movies that arouse implicit power motivation do not lead to a progesterone surge (Schultheiss, Wirth, & Stanton, 2004; see also Wirth & Schultheiss, 2006). Finally, situations that foster close, intimate exchange between two people also raise progesterone levels; mere collaboration on a task does not produce the same effect (Brown, Fredrickson, Wirth, Poulin, Meier, Heaphy, Cohen, & Schultheiss, 2009).
The link between progesterone and affiliation motivation may involve the neuropeptide oxytocin, which in mammals is a key player in attachment processes and directly regulates progesterone synthesis and release in the gonads. Another pathway is the hypothalamic-pituitary-adrenal axis, in which progesterone may be released as a by-product of stress hormones and is potentially involved in the down-regulation of the stress response (Wirth, Meier, Fredrickson, & Schultheiss, 2007). Further research in the HuMAN Lab will explore the contributions of these pathways to affiliation-induced progesterone release.
Recently, the HuMAN Lab has begun to examine a possible role of implicit motives as vulnerabilities to specific stressors. This line of research is based on the assumption that events and stimuli that are commonly assumed to be stressful are in fact only stressful to the extent that they represent an obstacle or frustration to the satisfaction of a strong implicit motive. Evidence supporting this hypothesis comes from research on the effects of a social defeat on the release of cortisol, a hormonal marker of stress. Only individuals high in implicit power motivation respond to this type of event with rising levels of cortisol, whereas individuals with a weak power motive show virtually no increases of cortisol (Wirth, Welsh, & Schultheiss, 2006). These results are consistent with research that shows that people who fail to make progress toward effectance-related goals in their daily lives become unhappy only to the extent that they possess a strong implicit power motive (Brunstein, Lautenschlager, Nawroth, Pöhlmann, & Schultheiss, 1995; Brunstein, Schultheiss, & Grässmann, 1998). The HuMAN Lab plans to further explore the relationship between motivational frustration and stress axis responses (see also Wirth & Schultheiss, 2006).