Neural And hormonal mechanisms for aggression

• The Limbic System (Neural Mechanisms)


  A central area of the brain that regulates emotional urges.
• AO1 - The Limbic System (Neural Mechanisms)


  Firstly, the hippocampus is involved in the formation of long-term memories which allows animals/humans to compare a current threat with similar past experiences. For example, if an animal who has previously been attacked encounters that or a similar animal again, they may be more likely to respond in a fearful or aggressive manner. Impaired hippocampus function also prevents the nervous system from putting things into meaningful context and may lead to amygdala to respond to sensory stimuli with aggression.

  
  

  Secondly, the most important structure linked to aggression by far is the amygdala whose role is to process emotion. If the amygdala in humans malfunctions due to a tumour, damage or atypical development, then this can lead to raised levels of testosterone, making aggression more likely.

  
  

  Finally, the hypothalamus is responsible for the regulation of the autonomic nervous system, which in turn regulates responses to emotional circumstances. Therefore, damage to this area can result in an inappropriate aggressive response to a perceived threat
• AO3 - Research And Evaluation (Neural Mechanisms)

  In support, animal studies show that if certain areas of the amygdala are stimulated electrically, then the animal will respond aggressively by snarling. If these areas of the amygdala in animals are removed, then the animal will no longer respond in the same way. This provides evidence that the amygdala located in the limbic system may be responsible for aggressive behaviour. However, Humanists argue that humans are qualitatively different to animals and that we are unable to generalise laboratory findings with animals to how humans may display aggression in real life situations. This means that we may be unable to generalise the research findings and is therefore an issue of ecological validity. An alternative explanation that provide a better understanding of human is aggression is provided by Frustration aggression theory. According to Dollard, frustration leads to aggression. This hypothesis is based on the psychodynamic concept of catharsis and views aggression as a psychological drive similar to a biological one such as hunger. If our attempt to achieve a certain goal is blocked such as trying to get past in a busy pub, we experience frustration. This in turn leads to swearing, an aggressive drive such as a violent fantasy or violence.
• AO3 - Research And Evaluation (Neural Mechanisms)

  Longitudinal Research by Pardini et al (2014) of 56 male participants with varying histories of violence using an MRI, discovered that participants with lower amygdala volumes, displayed higher levels of aggression and violence even after confounding variables were controlled. This suggests that the causes of aggression may be due to abnormalities in the limbic system. However, the research linking brain abnormalities to violence is mainly correlational. This means there is only a relationship between the limbic system and aggression and there are actually many individuals who have abnormalities in their limbic systems who do not demonstrate violent behaviour. This makes it difficult to establish cause effect. An alternative explanation is provided by Deindividuation theory. When we are part of a crowd, it is possible for us to lose our sense of identity and responsibility and in these circumstances, the social norms that usually keep us restrained with regards to antisocial behaviour are temporarily forgotten. We live for the moment, we stop monitoring and regulating our own behaviour and the result is antisocial/aggressive behaviour, for example crowd violence at football matches. This is a psychological explanation for aggression and therefore challenges the view that the limbic system is solely responsible for aggression.
• AO3 - Research And Evaluation (Neural Mechanisms)

  Further research by Sumer et al (2007) reported a case study of a 14-year-old girl who was showing aggressive, anger and rage. An MRI scan discovered a tumour in the limbic system and after the tumour was treated with drugs, the patient's levels of aggression returned within "normal" levels. This suggests that tumours in the limbic system could be the cause of aggressive behaviour. However, The role of the limbic system in aggressive behaviour is not clear cut. It should be noted that the limbic system is made of many components so it is not altogether clear which other parts may also be implicated. This suggests that different elements of the limbic system may interact leading to aggression, rather than the Amygdala or Hippocampus being the sole cause. The Sumer case study above was also of one individual only. This means that it is difficult to generalise to the causes of aggression in other individuals.
• AO1 - The role of Serotonin (Neural Mechanisms)


  Serotonin is a neurotransmitter involved in communication of impulses between neurons, it has a widespread inhibitory effect on the brain.

  In normal levels, it exerts a calming inhibitory effect on neuronal firing in the brain and serotonin typically inhibits the firing of the amygdala, the part of the brain that controls anger, fear and other emotional responses. Low levels of serotonin remove this calming effect with the outcome being that individuals may react in a more impulsive aggressive manner. Low levels of serotonin have also even been linked with self-inflicted forms of aggression including violent suicide.
• AO3 - Research And Evaluation (Neural Mechanisms)

  Virkkunen et al (1994) compared levels of a serotonin breakdown product in violent impulsive and violent non-impulsive offenders. The levels were significantly lower in the impulsive offenders, and they also suffered from more sleep irregularities (serotonin regulates sleep patterns). This supports the notion that impulsive aggression can be linked to neurotransmitters. However, Biochemistry is a deterministic explanation for aggression, removing the notion of free will and choice over our aggressive responses and instead laying the blame with neurochemistry in the brain. An alternative explanation is provided by Social Learning Theory who claim that Aggression can be learned by the observation of role models who may include; siblings, parents, peers and/or characters in the media. For example, if a child observes aggression and sees the model being rewarded, they may be more likely to imitate what they have seen (vicarious reinforcement). This is also true for reducing aggression and is why the promotion of positive role models is encouraged and restrictions on the internet or TV are in place to protect vulnerable children. Research shows therefore that children may learn how to perform aggressive behaviours, but repetition may depend on the consequences for the model.
• AO3 - Research And Evaluation (Neural Mechanisms)

  Raleigh et al (1991) found that monkeys fed on a diet high in tryptophan (which increases serotonin levels in the brain) exhibited decreased levels of aggression and vice versa. This also demonstrates that low levels of serotonin are linked to higher levels of aggression suggesting that aggressive behaviour "may" be biologically determined.
• AO1 - Testosterone (Hormonal Mechanisms)


  Testosterone is a male hormone produced mainly in the testes and is associated with sexual and aggressive behaviour. Males are generally more aggressive than females and at the age where testosterone levels are at their highest (21-35) there is an increase in male to male aggression. Attention has therefore focused on the male sex hormone testosterone, an androgen responsible for the development of masculine features. It may be that changes in testosterone influence aggression by increasing amygdala activity.
• AO3 - Research And Evaluation (Hormonal Mechanisms)

  A study in support by Wagner (1979) observed reduced levels of aggression in mice after they were castrated (reducing testosterone). Furthermore, the mice returned to normal levels of aggression after they were supplemented with testosterone injections. This supports the research that testosterone and aggression are linked. However, critics argue that animals and humans are qualitatively different and that the findings of animal studies can not be extrapolated to human aggression. An alternative explanation for aggression other than testosterone is provided by Frustration Aggression theory. Research by Geen for example required participants to complete a puzzle that was either impossible, had an interfering confederate, a confederate who insulted the participant or a control group containing no frustrating circumstances. Participants were then asked to give the confederate an electric shock if they made an error on a new task. The participants who were insulted gave out the strongest shocks on average, supporting the idea that perhaps frustration can lead to aggressive behaviour in real life situations for example road rage. However, these findings are the result of hypothetical scenarios which lack mundane realism also leading to poor predictive validity For example, someone may report a high level of aggression on paper but if the situation arose in a real-life scenario, the response would be more passive in nature, challenging the validity of hypothetical experiments. In conclusion, it could be argued that both of these explanations are linked. For example Frustration, linked to situations involving relationships (competition) may cause spikes in levels of testosterone contributing to an aggressive outburst.
• AO3 - Research And Evaluation (Hormonal Mechanisms)

  Van Goozen (1997) conducted a natural experiment on trans-gender sex-change patients. This is one of the few cases where research was actually carried out on humans. Findings revealed testosterone levels governed aggression. Males receiving testosterone suppressants became less aggressive. Females receiving testosterone, became more aggressive. This study demonstrates a direct link between testosterone causing aggression. However, Individuals with elevated testosterone levels "may" exhibit signs of aggression, but rarely commit aggressive acts, suggesting that social and cognitive factors play a mediating role and there is a difference between aggression (e.g. elevated anger) and physically aggressive behaviour suggesting that results of studies like Van Goozen should be taken with caution. For example, other researchers argue that increased levels of testosterone are the result of aggressive behaviour rather than being the cause! Higley et al (2006) for example found that testosterone can affect how an individual feels but not necessarily how they will behave.
• AO3 - Research And Evaluation (Hormonal Mechanisms)

  There are other studies of interest. For example, Dolan et al (2001) found a positive correlation between testosterone and aggressive behaviours in a sample of 60 offenders in UK maximum security hospitals with a history of impulsive violent behaviour, supporting the link between testosterone and aggression. However, this study is a correlation only meaning that it does not demonstrated cause effect. It may be other factors related to Psychological explanations that influences the behavioural response of the affected person. De-individuation for example, is a concept used to explain the behaviour of individuals when in a crowd. Usually, when we are easily identified by others, our behaviour is more likely to be restrained by social norms and we live in a society where aggressive behaviour is normally seen as unacceptable. When we are part of a crowd however, it is possible for us to lose our sense of identity and responsibility and in these circumstances, the social norms that usually keep us restrained with regards to antisocial behaviour are temporarily forgotten. We live for the moment, we stop monitoring and regulating our own behaviour and the result is antisocial/aggressive behaviour. The most obvious example being crowd violence at football matches, or peaceful protests that turn aggressive. Conditions that can contribute to aggressive behaviour include; darkness, drugs, alcohol, uniforms, masks and other disguises.
• Genetic explanations


  Individuals may be predisposed to criminal behaviour
• MAOA


  Causing low levels of serotonin linked to aggression
• AO1 - Genetic explanations including the MAOA Gene


  Genetic explanations propose that one or more genes predispose (put at risk) individuals for criminal behaviour. The evidence for Genetic explanations mainly comes from twin/adoption and family studies. MZ twins share 100% of their DNA whereas non-identical twins only share 50%. If a trait for example aggression, is found to be more common between MZ twins than DZ twins then we may be able to conclude that genetic factors are the cause rather than the environment.
• AO1 - Genetic explanations including the MAOA Gene


  A first genetic explanation is MAOA, a gene that is responsible for the production of an enzyme also called MAOA, responsible for the regulation of neurotransmitters such as serotonin in the brain. Certain versions of the MAOA gene lead to less production of the enzyme MAOA and result in irregular levels of serotonin (low). As we know that normal levels of serotonin regulate mood, low levels are thought to lead to aggressive behaviour. This Gene has been nicknamed the "warrior gene" with the condition of "Brunner Syndrome" who analysed the DNA of 28 Dutch family members with convictions for rape and attempted murder alongside other violent offences, discovering that they shared a particular gene that led to abnormally low levels of MAOA. A Mutated MAOA gene can also have implications for other neurotransmitters too:

  
• AO1 - Genetic explanations including the XYY Chromosome


  Secondly, there is evidence that males with an extra Y chromosome XYY 'supermale' may be predisposed towards violent crime. However, individuals with XYY are above average height and below average intelligence therefore it might be the latter characteristic (Low intelligence) that accounts for their over representation in prison populations rather than directly causing aggression.
• AO3 - Research, Discussion and Evaluation (Genetic explanations for Aggression)

  In support, adoption research by Mednick compared the criminal conviction rates of male adoptees with the conviction rates of their biological and adoptive parents. Results showed conviction rates of 20% of adoptees whose biological parents had convictions but who had been raised by non-criminal parents compared to only 13.5% of adoptees whose birth and adoptive parents were both non-criminals. This suggests that genetic factors do influence criminal behaviour. However, adoption studies can be criticised for the contamination effect as many of the adopted children may have stayed in contact with their criminal parents suggesting that any correlated criminal behaviour could have be learnt and not passed on genetically. An alternative explanation for aggression is provided by the impact of the media. Desensitization for example, is when continued exposure to violence within gaming may have a desensitization effect and the individuals playing these games will also get an experience of positive reinforcement from using violence. (Physiological). This may encourage aggressive behaviour away from the video game and challenge the view that aggression is genetic.
• AO3 - Research, Discussion and Evaluation (Genetic explanations for Aggression)

  McDermott used 78 male University students in a controlled setting asking them to complete an online vocab task where they earned money. They were then told an anonymous partner online could choose to take money away from them and were given the option of whether to punish the (fictitious) opponent by having them eat varying amounts of hot sauce. This would cost them money. Low-activity MAOA subjects were more likely to issue the punishment which implies that MAOA does influence aggressive behaviour. However, this experiment lacks mundane realism using a highly artificial task and punishment, questioning whether the results are generalisable outside of the lab to other people and why they become aggressive in real life situations. Genetic explanations such as MAOA also do not help us to understand why others who do not possess the mutated gene may act aggressively and fail to help us understand why females become aggressive known as Beta Bias.
• AO3 - Ethical Implications (Genetic explanations for Aggression)


  Critics have argued that if Genetic factors can account for violent behaviour then what are the implications for the criminal justice system? Although offenders could still be held accountable for their actions, does genetic research suggest that offenders are not fully responsible for their behaviour? If this is the case, what are the implications for punishment and should scientists be focused on identifying those at risk and preventing future offending?
• AO3 - Research, Discussion and Evaluation (Genetic explanations for Aggression)

  Coccaro et al. (1997) compared monozygotic versus dizygotic twin pairs. In this study, twin pairs were examined for the concordance of criminal behaviour for both twins. In cases of monozygotic or identical twin sets, the siblings are genetically identical (100% same genes) whereas in dizygotic or fraternal twin sets, the siblings are merely genetically similar (50% same genes). The MZ twin pairs were found to have a 50% concordance whereas DZ twins were only 19%. This research supports the role of genetics in aggression as the twins that were genetically identical, i.e. 100% of the same genes, were more likely to display criminal behaviour than the twins that only shared 50% of the same genes. However, twin studies are criticised for assuming that identical twins have identical environments. Whilst they may be raised in the same household by the same parents, their life experiences, particularly the impact on long term development of traumatic events when young could drastically differ. This questions the validity of twin research and aggression. Vassos et al (2014) in a meta-analysis study found no evidence for a single gene (such as MAOA) and aggressive behaviour, casting doubt that there is a single (candidate) gene responsible for aggression and that it may require hundreds of thousands of genes in complex interactions for there to be any effect at all. Very different resultswere found by Vassos et al (2014). in a meta-analysis study they found no evidence for a single gene (such as MAOA) and aggressive behaviour, casting doubt that there is a single (candidate) gene responsible for aggression and that it may require hundreds of thousands of genes in complex interactions for there to be any effect at all.
• AO3 - Research, Discussion and Evaluation (Genetic explanations for Aggression)

  Most genetic research makes reference to "violent" crime; however many crimes are non-violent for example fraud, drug use or theft. This means that genetic explanations fail to help us understand why these individuals commit these types of offences.
• AO3 - Research, Discussion and Evaluation (Genetic explanations for Aggression)

  Frazzetto (2007) did find an association between MAOA and aggression, but only if the individual had experienced significant trauma such as sexual or physical abuse when younger. This suggests that nature/nurture interplay provides a more comprehensive understanding of the links between genetics, the environment and aggression rather than the MAOA theory alone.