The association between testosterone levels and violent behaviors among females .. The relationship between testosterone and aggression: a meta- analysis. The relationship between testosterone and aggression: a meta-analysis. Add to My Bookmarks Is part of Journal. Title: Aggression and Violent Behavior. Aggressive behavior arises in the brain through interplay between .. The relationship between testosterone and aggression: A meta-analysis.
Man is inclined to affirm his personality by trying to be distinguished and gain influence and power in his career, in sports and in everyday life, by competing with others.
Acting in a dominant way of any kind may include violent acts, as is the case in prisoners. However, these dominant traits are usually manifested by angry faces or verbal aggression in trials to dominate or to be a winner in competitive tasks Physical and mental competitive tasks have been found to be associated with higher baseline values and more often with fluctuations of testosterone. Studies with a limited number of subjects have shown a positive relationship of testosterone with aggressive phases of the game in judo contests and hockey players 46 In dominance contests taking place in political elections, voters in democratic elections exhibit biological responses as if they had personally participated in the political contest.
In sports it has also been reported that winners have higher testosterone levels than losers Fans of sporting events also experience testosterone changes More sensitive manifestations to subtle aggressive stimuli are regarded to be measures of aggressiveness obtained in the laboratory through paradigms using various combinations to provoke aggressive reactions 3. In the Taylor Aggressive Paradigm TAP the participant competes against a factitious opponent, to whom he delivers an intense shock if he loses the trial.
With this test it was reported that baseline testosterone concentrations, despite individual differences, were positively correlated with the intensity of the aggressive reaction. In PSAP, stealing money from a factitious opponent in a trial to earn money is considered to be an aggressive act as it represents intent to cause harm to the opponent. Higher baseline testosterone that was found in individuals who rejected unfair offers, was interpreted as confirming this positive relation Using PASP and measuring salivary testosterone, it was demonstrated that changes in testosterone were positively correlated with aggression.
It was also found that an increase in testosterone during the PASP predicted subsequent willingness to choose competitive tasks 328 Studies of aggressive behavior and testosterone in the delicate years of adolescence yielded conflicting results that can be understood if one takes into consideration that at each age of puberty there is great inter-individual variability of psychological maturation and an even greater variability of testosterone secretion because of the asynchronous progress of pubertal development Aggression research in human studies has revealed an interesting property of testosterone dynamics, its rapid fluctuations provoking reactive aggression in response to stimuli.
It has been shown by competition paradigms in the laboratory, that short term fluctuations of testosterone were associated with eliciting aggressive behavior. These findings indicate two important features of testosterone physiology, a changes in testosterone levels may be more important than baseline values in relation to aggressive behavior, b and more significantly, testosterone by its rapid increase in response to a variety of stimuli, both physical and mental, is entitled to hold a position in the group of stress hormones.
Rapid fluctuations of testosterone are believed to be effected by non-genomic actions, mainly through the G protein of the membrane since the DNA reaction with an androgen receptor takes time The neurons of the prefrontal area, the hypothalamus and amygdala which are concerned with aggression, express significant quantities of androgen and estradiol receptors, along with the enzymes necessary for the steroidogenesis of these hormones.
The local production of testosterone in neuroendocrine neurons introduces a new factor into the interpretation of the interplay of this hormone with aggressive manifestations.
Locally produced testosterone and estradiol coupling with the receptors may receive a greater variety of enhancing or diminishing influences and these could modulate their effect on aggressiveness more than the testosterone produced by the Leydig cells, which are only stimulated by luteinizing hormone LH.
Testicular and locally produced testosterone multiplys, and its action is diverse due to its transformation intracellularly into dihydrotestosterone DHT and estradiol by the enzymes 5a-reductase and aromatase respectively, which are also expressed in the neurons associated with aggression. The testosterone metabolite androstenediol acting on GABA receptors may be another factor for the action of testosterone.
The effect of testosterone action on the brain begins in embryonic life. Testosterone receptors are expressed in the fetus earlier than the biosynthesis of testosterone which occurs in the seventh to eighth week of pregnancy. In the fifth month, the testosterone values in male fetuses reach a peack with levels approaching those of adult men.
This secretory surge lasting for a few weeks inundates the brain with testosterone, inducing anatomical and organizational changes that mark the sex differentiation of the male brain in adulthood 7. With these technologies that permit the visualization and mapping of brain areas when it has been aroused metabolically in response to stimuli, hopes are born of penetrating previously unknown domains of psychic functions and emotions, aspirations similar to those expressed for the exploration of the universe after man first stepped on the moon.
Case studies of patients with traumatic brain injuries or suffering from certain neurological disorders had provided vague information on the location of brain regions that might be associated with aggression.
In the modern era, investigations are conducted with a higher degree of sensitivity with the aid of neuroimaging technology that permits the scanning of brain activation.
The relationship between testosterone and aggression: a meta-analysis | Northumbria University
A meticulous review of 17 neuroimaging studies by Buflein and Luttrell indemonstrated that the prefrontal lobe, temporal lobe and subcortical structures in the hypothalamus and amygdala are associated with aggressive and emotional behavior in a complex play of interconnections The total number of subjects in these 17 publications wasof which were studied with matched controls and the majority of the subjects were accused murderers or murderers and patients with mental diseases.
Locally produced and circulating testosterone coupled with intracellular androgen receptors, reacts with the G protein of the neuron membrane and this activates the amygdala enhancing its emotional sensitivity. The amygdala plays a pivotal role in the neuroendocrine network by controlling perception and processing emotions. Cortisol receptors are also expressed in amygdala neurons as well as in serotoninergic receptors. These two chemical agents act antagonistically to testosterone in the manipulation of subcortical emotional activity and the restraining interference of the prefrontal cortex.
The gonadotropin-releasing hormone GnRH - LH - testosterone axis is closely linked with the corticotropin-releasing hormone CRH - adrenocorticotropic hormone ACTH - cortisol axis, and each of their end products, testosterone and cortisol respectively, influences the opposite axis In a pilot study of salivary testosterone and cortisol interrelationships it was found that higher testosterone levels and lower cortisol levels are associated with higher levels of anger Testosterone in the hypothalamus exerts an inhibitory action on CRH and the antidiuretic hormone induces a reduction in cortisol production.
More pronounced is the inhibitory effect of cortisol on GnRH. Stressful situations, such as trauma and the like, inflict significant inhibition on testosterone secretion. High testosterone levels or an increase in basal concentrations are associated with aggressive manifestations, whereas high cortisol concentrations are linked to submissive behavior.
The biological balance between testosterone and cortisol has a psychological equivalent. Motivational drives are mediated by punishment and reward and expressed by approach and avoidance tendencies, sensitivity to punishment is reduced when testosterone levels increase and this means that less fear is manifested in aggressive behavior, whereas the high cortisol levels released in stressful situations increases punishment sensitivity and avoidance, resulting in the choice of flight behavior.
At the neuronal level of this hormonal imbalance, testosterone activates emotional processes in the amygdala increasing the resistance of this subcortical structure to prefrontal inhibiting activity and cortisol facilitates cognitive control on impulsive tendencies aroused by the emotional subcortical structures. The degree of impulsivity present also plays a significant role in the activity of the emotional subcortical brain and this adds a third factor to the testosterone-cortisol balance, serotonin 35 Clinical studies have shown that the serotoninergic system regulates impulses and aggressiveness, as it has activating and inhibitory receptors in the prefrontal and the subcortical areas.
Blood serotonin 5-HT and its metabolites found in the cerebrospinal fluid are negatively related with aggression and selective 5-HT reuptake inhibitors have been shown to exhibit aggression lowering effects A recent PET study In 17 males of serotonin 5-HT1a inhibitory receptors binding potential in the prefrontal area and midbrain, demonstrated a higher number of 5-HT inhibitory receptors in the prefrontal area in subjects with the higher self reported aggressive scores Facial expressions of anger, a common social aggressive behavior, have also been used in protocols for studying the relationship of testosterone with aggressiveness.
An investigation in a group of 21 healthy males of the influence of blood testosterone levels on amygdala activation during an emotion recognition task, demonstrated a significant correlation between testosterone and amygdala reactivity to angry and fearful faces It is of interest that the impact of testosterone on the amygdala response was observed to be within the normal range of blood testosterone concentrations.
Recently a new influencing factor on aggressive behavior has emerged: The length of the trinucleotide CAG repeats in the promoter region of the human androgen receptor has been found to be associated with aggressive behavior. In a large scale study in India reported by Rajender et al. Free testosterone was also found to be more positively related to aggressive risk taking in adolescents with shorter CAG repeat length The clinical implications, however, of these and other studies of the genetics of human aggression is too early to be fully evaluated The theory emerging from these studies is that prefrontal sections are centers which control the emotional signals coming from interconnected subcortical structures, by imposing a restraining effect to them.
Disorders of these centers that diminish their function leave subcortical activity uncontrolled to express aggressive behaviors. In simplistic phrasing, the conditions for manifesting aggression are either a diminished functioning of the prefrontal cortex in relation to subcortical structures or an increased activity of these structures in relation to the prefrontal cortex.
Testosterone, cortisol and serotonin are the major agents influencing this process, with testosterone activating aggression reactions and cortisol and serotonin acting antagonistically to testosterone to reduce its effect. Conclusions The goal of this review was to highlight the clinical data and the neuroimaging findings in man concerning the relationship between testosterone and aggressive behavior.
Atavistic residues of aggressive behavior prevailing in animal life determined by testosterone remain in man, attenuated and suppressed by familial and social inhibitions, but still manifesting in various intensities and forms from thoughts, anger, verbal aggressiveness, competition, dominance to physical violence. Testosterone plays a significant role in the arousal of these behavioral manifestations in the brain centers involved in aggression and on the development of the muscular system that effects their realization.
Several field studies have also shown that testosterone increases during the aggressive phases of sports games. Most of the studies, however, were conducted by self reported questionnaires, the accuracy of which is questionable.
This created the theory that fluctuations of testosterone may be more significant than basal values in the importance of testosterone estimation in relation to aggression. On the other hand, the rapid increase of testosterone in the above situations entitles testosterone to be characterized as a stress hormone. All the above studies have methodological limitations because of the small number of subjects and samples.
More creditability comes from a large survey conducted on normal men which showed higher normal values in subjects with aggressive personality or antisocial conduct It is of interest, however, that the administration of high doses of testosterone in normal men had no effect on the self reported aggression scores of the subjects. Aggressive behavior arises in the brain through interplay between the subcortical structures in the amygdala and the hypothalamus in which emotions are born and the prefrontal cognitive centers where emotions are perceived and controlled.
Locally produced testosterone is assumed to be more important in the process of aggressive arousal than testicular testosterone arriving in the circulation. The action of testosterone on the brain begins in embryonic life. During the fourth to fifth month of pregnancy a surge of fetal testosterone occurs reaching adult testosterone levels which induces anatomical and organizational changes in the male embryos brain. Even earlier at the DNA level, the number of CAG repeats in the genes of the androgen receptors appear to play a role in the expression of aggressive behavior.
Men with fewer CAG repeats have more active androgen receptors and enhanced testosterone action. Asynchronous psychological maturation and the variability of testosterone secretion depends on the stage of puberty, and this explains the inconsistent and conflicting results of the studies of testosterone relationship with aggression in adolescents. In adult males neuroimaging techniques that have permitted visualization of brain functions have shown that testosterone activates the amygdala enhancing its emotional activity and its resistance to prefrontal restraining control.
The degree of impulsivity is regulated by serotonin inhibiting receptors. The major agents of neuroendocrine influence on aggression in brain process form a triad: The implication of the article concerns mainly health policy and education as it analyses the role of testosterone in aggressive behavioral acts.
Please cite this paper as: Testosterone and Aggressive Behavior in Man. Int J Endocrinol Metab. Testosterone and human aggression: Such studies have enrolled individuals with psychiatric disorders 611criminals, rapists, or prisoners 8 Small sample size is also a limitation of many of these studies 781321and a majority of the studies are restricted to male participants 6 - 9.
In addition, almost all studies in the field have used a cross-sectional design. Thus, the findings of the current study may potentially help us increase our understanding of sex differences in biological mechanisms for violent behavior in a community sample. In line with some previous studies 15our study did not show an association between testosterone and violent behaviors among men.
Among violent men, however, testosterone levels had a positive and significant association with hostility 7.
Sex Differences in the Association Between Testosterone and Violent Behaviors
There are, however, studies suggesting that high testosterone levels in cerebrospinal fluid, serum, and saliva may predict aggressive behavior 22violent crime 1415and antisocial personality disorder 23among men.
Testosterone levels may also predict social presentation of masculinity and toughness 14among males. Our study documented a link between testosterone and aggressive behaviors among young female adults who lived in the inner city, while the effect of age, race, and education was controlled.
One study conducted among female adolescents has suggested that high levels of testosterone may predict conduct disorder On the other hand, there are studies that failed to show such associations with externalizing behaviors Results of previous studies on the association between testosterone and aggression are therefore not conclusive.
While some of the previous studies have reported a positive relationship between testosterone and aggressive behaviors, there are other studies reporting a negative or non-association between levels of testosterone and aggression 5 Human studies have suggested that higher testosterone levels may be linked to aggression, social dominance, and hyper-reactivity to status threats 25 Interestingly, individuals with psychiatric disorders that present impulsive aggression e.
Some researchers believe that it does not affect all forms of aggression, and that only those related to impulsive aggression in response to social threat are associated with testosterone There are, however, studies suggesting that the strength and direction of the association between testosterone and aggression may not be different among men and women Animal studies suggest that injection of androgens may result in increased aggressive behaviors among female primates Studies among humans have also suggested that androgen therapy may increase anger among women Another observational study also documented positive correlations between testosterone and aggression during early follicular and late luteal phases of menses These factors may also explain why sex differences may exist in the link between testosterone and aggression.
Future research should test the role of menstrual cycle phases as a possible moderator as well. The current study suggested that sex may moderate the link between testosterone and aggressive behaviors among young adults who live in urban areas.
Another study measured plasma levels of testosterone and also externalizing behaviors among 51 boys and 68 girls at age Only among males was there a positive correlation between androgen metabolites and externalizing problems. Such an association could not be found among women In contrast, another study suggested a link between testosterone and externalizing behavior in male adolescents, but not females. In this study testosterone was measured among 87, year-old adolescents 36 boys, 51 girlsand externalizing behavior was measured at age 8, 11 and 14 years.
Results suggested that plasma testosterone predicted persistent externalizing behavior among males, but not females Age may explain some of the conflicting results across the studies.
A meta-analysis of community and selected samples suggested that there might be only low to modest association between testosterone and aggression, with mean weighted correlations ranging from 0. Overall, these meta-analyses suggest that the testosterone-aggression association is equally strong in 12 to year-olds, as it is in 22 to year-olds, but that it may be less strong in age groups younger than 12, than in those who are older 534 The results of the current study were in contrast with the literature which suggests that a link between testosterone and violent behaviors exists among male, but not female individuals.
One of the many factors that may explain the inconsistency in these findings is the community versus clinical setting, which has been shown to be a determinant of these associations.
Literature has previously shown that many of the findings that can be found in clinical samples may not be easily replicated in a community setting Previous researchers have proposed mechanisms to explain sex differences in the link between testosterone and aggressive behaviors One possible reason is that women have lower levels of testosterone and aggressiveness compared to men One study found a rise in testosterone levels prior to a contest among men, but not women It has been suggested that the effect of competition mostly aggressive behaviors on increasing testosterone levels may only be present among men It is also plausible to attribute sex differences in the above studies to differential variations in the amount of testosterone among men and women.
Such variations may attenuate the observed correlations in one sex 5. For instance, those studies that show a smaller relationship between testosterone and aggression among females may be due to range restriction 5. However, we can argue that just because testosterone and aggressive behaviors are lower among females, it does not mean that the relationship does not exist among women.
In this view, higher levels of testosterone lead to more aggressive behavior, irrespective of the fact that the range may be more limited among women. Finally, it may be easier to obtain accurate testosterone measurements in females, due to less diurnal variation, a phenomenon that is in contrast with the expected range restriction among females 5.
The current study may also have public health implications. The aggressive behaviors observed in women who live in a very violent community may be under the influence of testosterone. Interestingly, the same finding could not be found among men. The study also suggested a role of education level on the aggressive behaviors of men. Thus, we may argue that aggressive behaviors may be more social and less biologically based among men. As social factors can be modified, and biological factors are less subject to change, interventions for the prevention of violence may be easier for men.
Future research should test the complex interactions between sex, gender, biology, and social environment in shaping the aggressive behaviors of residents living in violent communities. Acknowledgments The authors would like to thank Aurora Turek for her contribution to the drafts of this manuscript.
This study increases our understanding of the basis of sex differences in complex social and aggressive behaviors and may be of use in public health programs and policies to reduce such behaviors in urban areas.