Researches and Studies on Testosterone

Many hormones have been identified that regulate endocrine function. Steroid hormones tend to have a significant role in differentiation in sex cells as well as playing a critical role in development (Kawata, M., 1995). Testosterone is a specific steroid hormone that is classified under the group of steroid hormones known as androgens. Androgens are the group of steroid hormones that have masculinizing effects. Androgens affect the growth of pubic and axillary hair in both men and women but are more pronounced in the secondary sexual development of men (Holst, J.

P., Soldin, O.P., Guo, T., & Soldin, S.J., 2004). Of all the androgens, testosterone is the most prominent. In primary sexual development, testosterone is responsible for testicular descent, spermatogenesis, and enlargement of the penis and testes (Nassar, G.N. & Leslie, S.W., 2018).

Testosterone is present in both males and females. In males, it is produced in the Leydig cells of the testes and in the ovaries of females. Sex hormones such as testosterone are controlled by the gonadotropin-releasing hormone (GnRH).

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GnRH is produced in the hypothalamus and stimulates the pituitary gland for the release Luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which both stimulate the gonads (Celec, P., Ostatn­kov, D., & Hodosy, J., 2015). In addition to its role in primary and secondary sexual characteristic development, testosterone can also affect brain behavioral functions Celec, P., Ostatn­kov, D., & Hodosy, J., 2015). As such, it is not surprising that hormones like testosterone can impact various psychological variables such as spatial abilities and memory.

For example, Pyter, Trainor, and Nelson (2006) conducted an experiment where they modulated the concentration of testosterone in adult male white-footed mice to measure the effect of that modulation on the performance of the mice in a water maze. In this study, there were two independent variables: testosterone modulation and photoperiod”day length. The mice were either maintained in a long day, which was 16 hours of light exposure per day, or a short day, which was 8 hours of light exposure per day for 14 weeks following a modulation of testosterone via castration with a saline implant or castration with testosterone replacement. The mice were then tested on spatial learning by the completion of a water maze. Results of this study showed that castrated mice with testosterone replacement exposed to short days had enhanced water maze performance, indicating better spatial learning.

The long day mice showed no difference between testosterone modulations. In another study conducted by Spritzer, Gill, Weinberg, and Galea (2007), spatial working and reference memory was measured among castrated and sham-castrated male rats. In this study, eight rats were castrated and eight were sham-castrated. All rats were compared on their performance in a working-reference memory radial arm maze and a version of the Morris water maze. Results of this study showed that the castrated rats had more working memory errors than the shams, but fewer reference memory errors when completing the radial arm maze. There were no significant results from the Morris water maze. According to the study, the results indicated that androgens such as testosterone improve working memory but impair reference memory. Previous empirical research has found that testosterone can have specific effects on other related memory factors. Particularly, working memory has been found to be correlated with increased testosterone levels (Cherrier, M.M. et al., 2001).

For instance, a study was done that measured testosterone levels in healthy men related to amygdala reactivity and memory performance (Ackerman et al., 2012). In this study, 234 healthy men were exposed to pictures from the International Affective Picture System. The men were shown these images to be encoded during functional MRI (fMRI). Ten minutes after exposure, participants completed a free recall test. Results of this study showed that if the men had higher testosterone levels, which subsequently led to increased activity in the amygdala, they demonstrated a higher level of freely recalled pictures (Ackerman et al., 2012).

A different study conducted by King, Kurdziel, Meyer, and Lacreuse examined the effects of testosterone on attention and memory for emotional stimuli in male rhesus monkeys. In this study, the macaques were exposed to modulated levels of testosterone and then exposed to various social stimuli meant to elicit an emotional response that would potentially improve memory for such stimuli. The results of the study showed that testosterone did not enhance working memory for emotional stimuli.

A pilot study conducted by Davison et al., (2011) examines the way that testosterone improves verbal learning and memory in postmenopausal women. In this study, nine postmenopausal women were either given a transdermal testosterone spray or a placebo for 26 weeks. The women were all tested fpr the International Shopping list task at baseline, where they showed not significant difference. They were then tested using the same measure at the end of the 26 weeks. Results of the study showed that there was improved cognitive performance in verbal learning and memory among postmenopausal women as a result of testosterone modulation. Based on the noted findings, evidence suggests that testosterone at increased levels can increase working memory measures. Another issue, however, involves the type of experimental methodology used to modulate such hormone levels. Past studies have used various treatments to increase the levels of testosterone. The use of injection has been one frequent method used to administer testosterone in both non-human subjects such as the study conducted by Pyter, Trainor and Nelson (2006) involving white-footed male mice as well as human participants such as the study done by Ackerman et al., (2012).

Interestingly, this begs the question if other non-invasive techniques have been used to equally modulate testosterone levels. Indeed, certain behavioral endocrinology research has shown that various types of competition, as well as competitive tasks, can increase testosterone levels. Bernhardt, Dabbs, Fielden, and Lutter (1998) suggested that testosterone is naturally modulated among fans at sporting events dependent on the vicarious experience of winning or losing. Several studies have considered the impact of testosterone increase related to vicarious competition. Bernhardt et al., (1998) for example, collected saliva samples from two groups of men before and after a sporting event. The first group was eight male fans attending a basketball game and the second group was 21 males watching a televised World Cup soccer game. Testosterone levels were measured in saliva samples provided by the participants before and after the competition they were viewing. Results showed an increase in testosterone levels of the fans whose team won and decreased testosterone levels for the fans whose team lost. These results indicate that vicarious competition can influence natural testosterone modulation.

Additionally, Meij et al., conducted a study that looked at the testosterone and cortisol release among Spanish soccer fans during the 2010 FIFA World CUP soccer game. Results of this study showed no increase of cortisol or testosterone in fans after the victory of the Spanish team, however, there was an increase in these levels while watching the competition. This could indicate that the excitement while watching vicarious competition increases levels of testosterone and cortisol. The present study will be examining if the modulation of testosterone visa watching a competition and experiencing it will improve working memory. Previous studies have shown that testosterone can be modulated via vicarious competition.

Different levels of vicarious competition will be presented in this study to modulate testosterone levels among participants. Other studies have shown that increased testosterone improves working memory tasks, which will be measured in this study by a verbal recall test. Since testosterone can be modulated by vicarious competition, it seems appropriate that different levels of competition will cause participants to have different performances on verbal working memory tasks.