An experimental study on young males showed that applying a single dose of testosterone in the form of gel to participants upper arms and shoulders reduces their willingness to delay gratification of sexual impulses. The study was published in Psychoneuroendocrinology.
Testosterone is the major sex hormone in males. Produced mainly in the Leydig cells of testes, it plays the primary role in sexual differentiation and functioning. In many mammals, it regulates both the ability to engage in sex and sexual desire. Studies on humans have revealed that it also has a role in decision making and psychological processing of rewards. For example, higher testosterone levels have been found to make a person more willing to take risks in experimental settings.
Testosterone levels normally fluctuate in humans. Some of the early scientific studies showed that watching a sexually explicit movie leads to the elevation of testosterone levels in healthy young men. The same was found to happen when men visit sex clubs, engage in sexual activities or are exposed to certain smells.
To investigate the effect of testosterone on sensitivity to sexual rewards and sexual impulsivity, Yin Wu and her colleagues conducted an experiment on a group of 140 healthy young men, aged between 18 and 26 years. Participants were randomly divided into a testosterone treatment group and a placebo group. The experiment was double blind, meaning that neither the participants nor the experimenters conducting the experiment knew which participant was in which group.
All experimental sessions lasted for 4 hours. In the experimental group, a male research assistant applied topical testosterone gel to participants shoulders and upper arms. The placebo group underwent the same procedure with the only difference being that the gel applied did not contain testosterone, but was just an odorless hydroalcoholic gel that looked the same as the testosterone gel (placebo gel).
After the gel application, participants completed 60 trials in which they were presented a fuzzy sexual figure for half a second and faced with a choice to wait 1 second and be presented with the clear version of that picture for 1 second (smaller-sooner reward) or wait a longer period (3s-15s) and be presented the clear version of the picture for 3 seconds (larger-longer reward). Participants were explicitly told that reacting faster would not lead to them being exposed to more pictures in total. Pictures used in the study were 60 pictures of nude women.
“We found that testosterone administration increased preference for the smaller-sooner option and induced steeper discounting for the delayed option,” the researchers wrote. In other words, participants that received testosterone choose more often to be shown the picture of a nude woman after just 1 second compared to the control group. They were less willing to wait for a longer interval in order to be able to view the picture for a longer interval – 3 seconds. This happened in spite of the fact that there were no differences between the two groups in impulsivity as a trait, as assessed by the Barratt Impulsivity Scale (BIS-11).
“Taken together, these findings suggest that the administration of a single testosterone dose increases impulsivity for sexual rewards. Acute testosterone elevations in response to sexual stimuli are phylogenetically conserved, which might indicate that they have evolved to modulate physiological and behavioral mechanisms that maximize reproductive fitness,” the study authors conclude.
The study highlights an important mechanism underlying sexual behavior of men. However, it also has limitations that need to be considered. Notably, the study used sexual pictures, which are, so-called, secondary rewards. The effects might be different in situations when people are faced with primary rewards (e.g., sexual intercourse). Also, the study did not consider the relationship status of participants nor their baseline testosterone levels.
The paper, “Exogeneous testosterone increases sexual impulsivity in heterosexual men”, was authored by “Yin Wu, Jianxin Ou, Xin Wang, Samuele Zilioli, Philippe N. Tobler, and Yansong Li.
