 18. Implicit Motives  397
drop in testosterone after a defeat (see also 
Vongas & Al Hajj, 2017).
While studies show that n Power also pre -
dicts testosterone increases in response to 
dominance contests in women, there is evi -
dence for a more critical role of estradiol in 
women, with n Power predicting increased 
estradiol after winning and decreased estra -
diol after losing (cf. Oxford, Tiedtke, Oss -
mann, Özbe, & Schult  heiss, 2017; Stanton 
& Schult  heiss, 2007). Stanton and Schult -
heiss (2007) therefore speculated that es -
tradiol may represent a female dominance 
hormone, similar to the role testosterone 
fulfills in males. Transiently elevated tes -
tosterone or estradiol after a victory may 
help reinforce successful behavior and keep 
the individual motivated for another fight, 
just as transiently depressed levels of these 
hormones after a defeat inhibit unsuccess -
ful behavior and help avoid another costly 
fight (Mazur, 2015; Stanton & Schult  heiss, 
2009).
Situational power challenges or stressors 
with their effects on SNS arousal and stress 
hormone release make power-  motivated in -
dividuals more susceptible to cardiovascular 
problems, immune system changes, and ill -
ness (Jemmott, 1987; McClelland, 1989). 
Power stress has been shown to lead to el -
evated and prolonged SNS activation and 
suppressed immunocompetence in power- 
motivated individuals and, as a consequence, 
to more frequent and severe illness in these 
individuals (for a summary, see McClelland, 
1989).
n Power also predicts brain activation re -
sponses to power-  related incentives. Schult -
heiss, Wirth, et al. (2008; see also Hall et al., 
2010) used high- and low-  dominance facial 
expressions of emotion as stimuli in a func -
tional magnetic resonance imaging (fMRI) 
study. Individuals high in n Power showed 
increased brain activation in the striatum, 
the OFC, and the insula (a cortical area in -
volved in subjective emotional experience), 
particularly in response to high-  dominance 
anger faces. Hall and colleagues (2010), in 
a reanalysis of this study, also found that 
n Power predicted increased amygdala re -
sponses to such faces. These findings suggest 
that n Power is tied to several key areas of 
the motivational brain involved in incentive prediction and evaluation as well as in in -
strumental learning.
The Biopsychology of  the Affiliation  Motive
Research on the biological aspects of n Af -
filiation suggests an association of this moti -
vational disposition with indicators of para -
sympathetic nervous system (PNS) activity, 
better cardiovascular health, and better im -
mune system functioning (for summaries, 
see Jemmott, 1987; McClelland, 1989; for 
a recent finding, see Prestele, Gerstenberg, 
Hagemeyer, & Geisler, 2016). Another line 
of research points to a link between n Affili -
ation and the steroid hormone progesterone 
(see Schult  heiss, 2013b, for an overview). 
For instance, women who take oral contra -
ceptives, which contain progesterone, have 
higher n Affiliation scores than women not 
taking the pill or men (Schult  heiss, Dar -
gel, & Rohde, 2003; Schult  heiss & Zimni, 
2015). Also, higher n Affiliation scores are 
preceded by greater increases of proges -
terone in the course of women’s menstrual 
cycle (Schult  heiss et al., 2003). In an attempt 
to synthesize findings on the link between 
progesterone and n Affiliation, Wirth (2011) 
has suggested that progesterone, through 
its effects on gamma-  aminobutyric acid 
(GABA) receptors in the brain, may help to 
down-  regulate HPA axis activation once it 
has been triggered by stressors. This account 
is consistent with the more general idea that 
social affiliation acts as a buffer against 
stress (Taylor, 2006), but also with the idea 
that, conversely, overwhelming stress may 
disrupt one’s ability to affiliate with others 
(Sandi & Haller, 2015). Although research 
on n Affiliation has only focused on pro -
gesterone as a specific marker so far, it may 
also be associated with other hormones and 
transmitters, such as oxytocin and opioids 
(see Gangestad & Grebe, 2017).
The Biopsychology of  the Achievement  Motive
The biological correlates of n Achieve -
ment have received the least attention so 
far, despite the fact that clues to such cor -
relates emerged almost from the beginning 
of n Achievement research (e.g., Mücher & 
Heckhausen, 1962). For instance, Bäumler 
(1975; cf. Schult  heiss & Brunstein, 2005) 