Aggression

The limbic system

Coordinates behaviours which satisfy emotional and motivational urges, like fear and aggression. The limbic system includes the amygdala which is responsible for evaluating the importance of sensory information and so if certian parts of the amygdala are stimulated, this can cause an animal to respond aggressively. This also includes the hippocampus which is involved in the forming of LTMs, meaning that an animal can compare curent threats with past experiences to think how to respond to a current threat.

Serotonin 

When serotonin is at normal levels, it has a calming inhibitory effect on neural firing, for example, it can inhibit the firing of the amygdala. Low levels of serotonin remove this effect and this causes the amygdala to become more active when stimulated. Also, low levels of serotonin have been linked to an increased susceptibility to impulsive behaviour. 

Testosterone

A hormone which produces male characteristics, one of which is aggressive behaviour. Levels reach a peak in young males. If the source of testosterone is removed in different species, this typically causes lower levels of aggression but when testosterone injenctions are given, these increase aggressive behaviour. Testosterone is thought to be linked because men are generally more aggressive than women and have higher levels of testosterone. Also, violent criminals have higher levels of testosterone than non-violent criminals. Changes in testosterone levels appear to increase amygdala reactivity.

Evidence for the role of the hippocampus in aggression

Raine et al (2004) studied two groups of violent criminals: those who faced conviction and were seen as cold and calculating (‘unsuccessful psychopaths’) and those who had evaded conviction and were seen as acting impulsively (‘successful psychopaths’). MRI scans showed asymmetries in the hippocampus in the ‘unsuccessful’ group. The researchers suggested an imbalance in the size of hippocampus in hemispheres impaired the ability of the hippocampus and amygdala to work together, causing emotional information to be not processed correctly and inappropriate physical and verbal responses.

Miles and Carey (1997) did a meta-analysis of 24 twin and adoption studies that showed the role of genes in aggression. Found strong evidence for genetic influence in aggression. But, age was important. In younger years, genes and family environment were influential in aggression but in later years, the influence of their environment reduced and the influence of genes increased.

Caspi et al (2002) studied 500 male children and found a variant of the gene associated with high levels of MAOA (MAOA-H) and a variant associated with low levels (MAOA-L). The children with a MAOA-L variant were significantly more likely to exhibit anti-social behaviour later on in life but only if they had been maltreated as children.

Convictions for violent crimes are few compared with the violent crimes committed. The sample for many studies only represents a small minority of those involved in violent crimes. Also, offenders convicted of violent crimes are not always the most serious, persistent offenders - may explain why many studies have found little evidence of heritability for violence.

• More than one gene often contributes to one behaviour.
• There are also environmental factors which influence aggression.
• Genetic factors and environmental factors may interact with each other - genetic factors can affect what environmental factors have an influence and vice-versa.

These innate behaviours are called fixed action patterns (FAPs) which are produced by the innate releasing mechanism (IRM) and are triggered by a very specific stimulus i.e. the sign stimulus. Sensory recognition circuits are stimulated by the presence of the sign stimulus and they send a message to the IRM which then communicates with motor control circuits to activate the associated FAP of that sign stimulus. The ethologist Tinbergen, studied sticklebacks and found that a male stickleback fish will produce a pattern of aggressive behaviours when another male enters its territory; the sign stimulus is the sight of the fish’s red underbelly.

These innate behaviours are called fixed action patterns (FAPs) which are produced by the innate releasing mechanism (IRM) and are triggered by a very specific stimulus i.e. the sign stimulus. Sensory recognition circuits are stimulated by the presence of the sign stimulus and they send a message to the IRM which then communicates with motor control circuits to activate the associated FAP of that sign stimulus. 

Ethologists describe how not all aggressive behaviour involves fighting but can be ritualised in the form of threat displays. These are important as they help the contestants assess their strength and decide whether to escalate a conflict. This makes physical aggression less likely e.g. male gorillas use vocalisations and gestures (chest pounding) to intimidate their opponent without having to resort to physical aggression. Also, anthropologists found ritualised aggression in human cultures e.g. Fox (1978).

• Half of three to five year old children were exposed to adult models acting aggressively towards a Bobo doll (striking it on the head with a mallet, kicking it about the room) and half were exposed to models who were not aggressive towards the doll.
• After being exposed, they were frustrated by being shown attractive toys that they could not play with. Then, they were taken a room with toys, including a Bobo doll.
• Children in the aggressive condition reproduced a lot of the verbal and physical aggressive behaviour that the model had exhibited. Children in the non-aggressive condition showed virtually no aggression towards the doll.

• When people join large groups or crowds, this arouses the state of de-individuation. Being in a large group give people anonymity. A uniform and an altered consciousness increase the feeling of anonymity.
• Normally, when we are easily identifiable, our knowledge of social norms prevent uncivilised behaviour, including aggressive behaviour.
• But, anonymity diminishes the awareness of their own individuality. In a large group, each person feels anonymous so the larger the group, the greater the anonymity. Due their lack of awareness of their personal identity, they feel unaccountable of their actions. This means that they have less of a fear of evaluation by others and so the normal guilt and shame barriers can be overcome, resulting in more aggressive behaviour.

• Groups of four female undergraduates had to deliver electric shocks to another student to help with learning. Half had to wear bulky lab coats and hoods that hid their faces and were not referred to by name. The other half wore normal clothes and were given large name tags.
• In the de-individuation condition, participants were more likely to press the button giving electric shocks to the student. They held the button down twice as long as identifiable participants.

• A meta-analysis which looked at the effects of violent video games (the goal is to harm another character) and prosocial games (the goal is to benefit another character). They assessed the influences of these games on aggressive and prosocial behaviour, cognitions and emotions.
• They found a small average effect size (the difference between the two groups). Violent video game use was linked to an increase in aggressive outcomes and a decrease in prosocial outcomes. Prosocial games showed the opposite effect.

• Explanations based on the idea that under normal conditions, anxiety about violence inhibits its use but media violence may lead to aggressive behaviour by removing this anxiety.
• The more TV violence a child watches, the more acceptable aggressive behaviour becomes and the less anxious a child becomes about violence.
• Desensitisation often takes a long time and involves numerous exposures to TV and computer game violence. Linz et al (1989) described one indication of desensitisation as the reduction of physiological arousal (heart rate) when people are exposed to real violence after being repeatedly exposed to media violence.

Carnagey et al (2007) had participants either play a violent or non-violent video game and then they watched a short film showing scenes of real violence while their heart rate and skin conductance response were measured. Those who had played the violent video game had a lower heart rate and skin concordance rate while watching the film. This shows a physiological desensitisation to violence.

Explanations based on the idea that normally, anxiety about violence inhibits its use but exposure to media violence can remove this anxiety and therefore result in aggressive behaviour. Being exposed to violent media legitimises the use of real life violence as it undermines the social sanctions that usually inhibit aggressive behaviour. The justification of media violence is one of the ways that children can infer standards of acceptable behaviour. It can have a short-term and long-term effect. Media violence causes physiological arousal which makes it more likely someone will behave aggressively. In the long-term, prolonged exposure to media violence gives the message that violence is normal in everyday life.

Cognitive priming refers to a temporary increase in the accessibility of thoughts and ideas. Berkowitz (1984) proposed cognitive priming to explain the short-term effects of media violence. He proposed that when people are constantly exposed to media violent media, this activates thoughts about violence, which in turn, activate other associated aggressive thoughts. E.g. a violent film could temporarily lower the threshold for activation of these thoughts, making them accessible for a short time. Prolonged exposure to violent media can mean that someone has a lower activation threshold for aggressive thoughts, meaning these can be accessed more easily and can be used to process and interpret social information. E.g. Zelli et al (1995) found that priming of aggressive stimuli caused individuals to make hostile attributions about other people which can increase the likelihood of aggressive behaviour.