The hidden dimensions of the competition effect: Basal cortisol and basal testosterone jointly predict changes in salivary testosterone after social victory in men

Dominance struggles appear to affect hormone concentrations in many mammalian species, such that higher concentrations of testosterone are seen in winners of competitions, compared to losers. This so-called, “competition effect” has received inconsistent empirical support, suggesting that additional psychological (e.g., mood), situational (i.e., nature of the competition) and physiological (e.g., cortisol) variables might intervene in modulating testosterone fluctuations after social contests. We investigated possible interactions between the hypothalamic-pituitary-gonadal (HPG) axis and the hypothalamic-pituitary-adrenal (HPA) stress axis in predicting transient changes in testosterone after social victory or defeat on a familiar competitive task. In particular, the present study examined the dual-hormone hypothesis - proposing that baseline cortisol potently modulates the competition effect (Mehta and Josephs, 2010) - in a sample of healthy young men engaged in head-to-head competition on a widely played commercial videogame, Tetris. We found a significant interaction between HPG and HPA axes status and the competition effect on testosterone in the randomly assigned videogame winners, such that winners with a pre-competition combination of high baseline testosterone and low baseline cortisol exhibited significantly greater post-competition testosterone concentrations. The randomly assigned videogame losers showed significantly decreased post-competition levels of testosterone. Possible biological and evolutionary mechanisms underlying this phenomenon are discussed.