Biological explanations of aggression Neural and hormonal mechanisms and aggression 1

Essentially the argument is Low levels of serotonin High levels of dopamine High levels of testosterone Low levels of cortisol..... are associated with aggression 2

Biochemical influences on aggressive behaviour – Background FYI Since the 1980s, there have been various high profile cases where hormonal fluctuations surrounding PMT have been used as grounds to claim temporary insanity In some cases, a murder charge was reduced to manslaughter when PMT was taken as a contributory factor Lawyers argued that the females were acting as automatons of their own body In other words, the aggressive act is caused by uncontrollable hormonal changes associated with monthly cycle. 3

Nelson (1995) reviewed research in this field. Found that generally, a positive correlation between the level of androgens circulating in the body and aggressive behaviour in both male and female prisoners. (Androgens being male sex hormones, eg; testosterone) Argument weakened slightly as androgens not measured at the precise point of aggression so correlational only – other factors could be involved. 4

Testosterone An androgen produced in male testes and in the adrenal cortex The release of the hormone is rhythmic and follows a natural circadian rhythm Evidence seems to point to androgens having an effect on aggression, EG: during puberty Castrated male mice overall levels of aggression fell but if given testosterone injections aggression levels increase( Wagner, Beuving & Hutchinson (1979) 5

So, do hormones cause aggression? In males, androgens encourage aggressive behaviour, dominance, impulsiveness and competition Pillay (2006) Testosterone long associated with athletic qualities – when comparing 94 male and female athletes testosterone levels differed with the higher levels being in the more aggressive sports Simpson (2001) – argues that testosterone only one of myriad of factors and that effects of environmental stimuli have been found to correlate more strongly at times. 6

Testosterone AO2 Dabbs et al (1987) – salivary testosterone levels were able to differentiate between violent and non-violent crimes Lindman et al (1987) – aggressive behaviour in drunk males positively correlated with testosterone levels Wagner et al (1979) castrated male mice showed decreased aggression which then increased when given testosterone again Archer (1991) and Book et al (2001) – meta analyses with slightly different results Wingfield et al (1990) – argue that testosterone levels rise in monogamous species in response to social challenges 7

Serotonin - NT Research suggests serotonin influences aggression levels Suggestion that serotonin may provide an inhibitory function, when comparing violent with non-violent criminals, serotonin levels were markedly lower in violent criminals ( Davidson, Putnam & Larson, 2000) Animals with serotonin levels manipulated and lowered show increased aggression (Monkeys / mice) Domestic pets have been bred for reduced aggression and have higher levels of serotonin than those in the wild Lenard (2008) Monkeys living in a social group were more likely to survive and be more sociable and integrated into the group if higher levels of serotonin. Those with lower levels, more likely to get injured or die young. 8

Serotonin Low levels associated with increased susceptibility to impulsive behaviour, aggression & violent suicide Mann et al (1990) – drugs which reduced serotonin increased measures of hostility and aggression in males (but not females) Scerbo & Raine (1993) – meta-analysis supports low level of serotonin but found no dopamine abnormalities 9

Dopamine AO1 Link less well established than serotonin Lavine (1997) – giving amphetamines (which increase dopamine) increases aggressive behaviour Buitelaar 2003) – giving anti-psychotics (which reduce dopamine) reduced aggressive behaviour in violent delinquents 10

Cortisol AO1 Cortisol mediates other hormones such as testosterone High levels of cortisol inhibit testosterone and so inhibit aggression So low levels of cortisol associated with increased aggression Virkuunen (1985) found low levels of cortisol in habitual violent offenders; Tennes & Kreye (1985) same in violent schoolchildren 11

AO2 / AO3 Findings on serotonin replicated in vervet monkeys (Raleigh et al (1991)) But issues of: – extrapolation – Ethics 12

AO2 Findings on serotonin also confirmed via studies on anti-depressants However Lenard (2008) cautions that serotonin not just linked to aggression: also to impulsive behaviour, depression, over-eating, alcohol abuse; violent suicide 13

AO2 Causal role of dopamine unclear Perhaps high levels of dopamine are an effect rather than a cause? 14

AO2 / AO3 Evidence conflicting on role of testosterone Studies showing positive correlation small samples and self-report measures Studies mainly correlational (eg. Wagner) so not possible to conclude that testosterone causes aggression Also testosterone not always associated with negative characteristics: improved sporting and spatial abilities also been found 15

AO2 clarification needed Need to distinguish between aggression & dominance Issue relates to the internal validity if the research as studies may be measuring different things, making comparison of results difficult 16

AO2 issues Gender bias evident as most research done on males (animals and humans) whereas it is known that there are differences between the genders in androgens Also cultural bias as most research conducted in western countries 17

AO2 debates Physiologically reductionistic to just consider role of biochemistry alone Also need to consider genetic factors and brain structure Eg. Phineas Gage suffered brain injury and showed heightened levels of aggression Also need to consider the contribution of environmental factors such as situational cues, temperature, noise, overcrowding, and the role of learning 18

AO2 application Clearly a very important & useful area of biopsychological research and theory as aggression associated with many anti-social phenomena in society, eg. numerous forms of crime, violence If the role of biochemistry can be understood it can perhaps be treated or managed Although there would be ethical issues associated with giving people drugs simply to alleviate aggression (ie. for social control), or male castration, even if it may be in the interests of multiple parties Could perhaps be treated more ethically through diet (tryptophan) and exercise 19