Aggression

Aggression: feelings of anger or antipathy, resulting in hostile or violent behaviour. Readiness to attack or confront. Different from assertiveness (firmness) or dominance. Two broad categories of aggression are commonly distinguished. One includes affective (emotional) and hostile, reactive, or retaliatory aggression that is a response to provocation, and the other includes instrumental, goal-oriented or predatory, in which aggression is used as a means to achieve a goal. Example of hostile aggression: person punching someone who insulted them. Example of instrumental aggression: armed robbery

Types of aggression:

• Direct aggression: attempt to hurt another directly
• Indirect aggression: attempt to hurt another without obvious face-to-face actions - spreading rumours or gossip, exclusion
• Hostile aggression: stemming from feelings of anger and aimed at inflicting pain
• Instrumental aggression: a means to some goal other than causing pain

Aggression can be examined in terms of its ability to help an animal survive and reproduce.

Violence and conflict: aggression can involve violence that can be adaptive in certain situations, and in terms of natural selection. Most obviously, this is the case in terms of attacking prey to obtain food, or in anti-predatory defense. It may also be the case in competition between members of the same species or subgroup, if the average reward outweighs average costs.

Gender: there is much variation in species, but generally the more physically aggressive sex is the male, particularly in mammals. In species where parental care by both sexes is required, there tends to be less of a difference. When the female can leave the male to care for the offspring, then females may be larger and more physically aggressive. Aggression in women may have evolved to be, on average, less physically dangerous and more covert or indirect (Campbell, 1999). An analysis across 9 countries found boys reported more in the use of physical aggression (Lansford et al, 2012). Boys are more physically aggressive, girls are more indirectly aggressive (e.g gossip, ostracism) (Richardson & Hammock, 2007). Evolutionary theory would explain that males behave aggressively so as to secure dominance and status

Numerous circuits within both neocortical and subcortical structures play a central role in controlling aggressive behaviour, depending on the species, and the exact role of pathways may vary depending on the type of trigger or intention.

In mammals, the hypothalamus and periaqueductal gray of the midbrain are critical ares. Electrical stimulation of the hypothalamus causes aggressive behaviour (Kruk et al, 1983) and the hypothalamus has receptors that help determine aggression levels based on their interactions with serotonin and vasopressin (Ferris, Melloni, Koppel, Perry, Fuller & Delville, 1997). These midbrain areas have direct connections with both the brainstem nuclei controlling these functions, and with structures such as the amygdala and prefrontal cortex.

Stimulation of the amygdala resulted in augmented aggressive behaviour in hamsters (Potegal, Hebert, Decoster, & Meyerhoff, 1996). In rhesus monkeys, neonatal lesions in the amygdala or hippocampus resulted in reduced expression of social dominance, related to the regulation of aggression and fear (Bauman, Toscano, Mason, Lavenex, Amaral, 2006).

Broad area of the cortex known as the prefrontal cortex is crucial for self-control and inhibition of impulses, including inhibition of aggression and emotions. Reduced activity of the PFC has been associated with violent/antisocial aggression (Paus, 2005)

The role of chemicals in the brain, particularly neurotransmitters, in aggression has also been examined.

A deficit in serotonin has been theorised to have a primary role in causing impulsivity and aggression (Bond, 2005). Low levels of serotonin may explain a vulnerability to impulsiveness, potential aggression, and may have an effect though interactions with other neurochemical systems. These include dopamine systems which are linked to attention and motivation toward rewards.

Norepinephrine may also influence aggression responses both directly and indirectly through the hormonal system, the sympathetic nervous system, or the central nervous system.

The hormonal neuropeptides vasopressin and oxytocin play a key role in complex social behaviours in many mammals, such as regulating attachment, social recognition, and aggression. Vasopressin has been implicated in male-typical social behaviours which includes aggression (Heinrichs & Domes, 2008)

Aggressive behaviour tends to increase with testosterone. There are noticeable sex differences in aggression. Testosterone is present to a lesser extent in females, who may be more sensitive to its effects. Animal studies have indicated a link between incidents of aggression and the individual level of circulating testosterone.

• Animals injected with testosterone become more aggressive (Moyer, 1983)
• Naturally occurring testosterone levels are significantly higher among prisoners convicted of violent crimes than among convicted of nonviolent crimes (Dabbs, 2000)
• Juvenile delinquents have higher testosterone levels than college students (Banks & Dabbs, 1996)
• Being in an aggressive, competitive, or sexual situation increases the production of testosterone (Thompson, Dabbs & Frady, 1990)
• Involvement in crime usually rises in the early teens to mid teens which happens at the same time testosterone levels rise and peak

Aggressive behaviours don't have to be learned. Young isolated rats and experienced rats use the same pattern of threat and attack (Eibl-Eibesfeldt, 1963).

There may be a genetic predisposition. There are few men that have 47 XYY karotype - extra Y chromosome among men. On average, men that have this extra chromosome are more aggressive (Sandberg, 1971). Deficiency of MAO-A "warrior gene" - regulates dopamine and serotonin levels (Moffat et al, 2002), aggressive only when abused as children.

"Culture of honour" in the US (Nisbett, 1993): white southern males more aggressive than northerners. Southerners more likely to be involved in homicide; but only in situations to protect honor, e.g in response to insults. The south is a herding society - they may need to be aggressive to protect their livestock. Cohen, Nisbett, Bowdle & Schwarz (1996): white male students (northerners and southerners) bumped by a confederate in the hall and insulted. Southern males more likely to think masculine reputation was threatened, had higher testosterone, became more upset and angry, and engaged in more aggressive behaviours.

Social-cognitive learning theory: people learn social behaviour through observation and imitation of others. Both positive and negative social behaviour.

Bandura's 1961 Bobo doll experiment aimed to investigate if social behaviours like aggression can be acquired by observation and imitation. Children watched an adult aggressively hitting a Bobo doll, or being non-aggressive with the doll. Children who observed the aggressive model made far more imitative aggressive responses than those who were in the non-aggressive or control groups. Boys imitated more physically aggressive acts than girls.

Frustration-aggression theory (Berkowitz, 1969): aggression is the result of blocking, or frustrating a person's efforts to attain a goal. Frustration causes aggression, but when the source of the frustration cannot be challenged, the aggression gets displaced onto an innocent target. The closer the individual is to their goal, the more frustrated they will become if it is interrupted. However, frustration does not always lead to aggression. It increases anger, and increases readiness to aggress. The frustration-aggression link depends on: the size and strength of the person responsible for your frustration, person's ability to retaliate, and proximity of the person. Likelihood of aggression is reduced when frustration is: understandable, legitimate, and unintentional.

Aggressive cues: these type of cues activate aggressive tendenceis via nonconscious automatic response making people react more aggressively than they would otherwise (Anderson et al, 1998). Weapons effect (as a cue): frustrated individuals more likely to be aggressive in the presence of weapons instead of neutral object (Anderson, 1998). Students made angry through negative feedback were more likely to deliver higher shocks to another student if they were in a room with a gun, rather than a badminton racket.

Physiological influence - alcohol: links between those prone to violence and their alcohol use. Those prone to violence and to use of alcohol are more likely to carry out violent acts (Navis, Brown, & Heim, 2008). Alcohol impairs judgement, making people much less cautious than they usually are (MacDonald et al, 1996). It also disrupts the way information is processed (Bushman, 1993). 

Pain and discomfort also increase aggression. Even the simple act of placing one's hands in hot water can cause an aggressive response. Hot temperatures have been implicated as a factor in a number of studies. One study completed in the midst of the civil rights movement found that riots were more likely on hotter days than cooler ones (Carlsmith & Anderson, 1979). Students were found to be more aggressive and irritable after taking a test in a hot classroom (Anderson et al, 1996). Drivers in cars without air conditioning were found to be more likely to honk their horns (Kenrick & MacFarlane, 1986).

Researchers have concluded that the media may have some small effects on aggression (Akert, Robin, Aronson, & Wilson, 2005). Actively watching violent video games has a stronger influence on aggressive behaviour. Games that directly promote violence increase: hostility, aggressive thoughts, and aggressive acts. Violent media numbs people to difficult, violent, and unpleasant events, and increases indifferences to real victims of violence. Repeatedly dehumanising the "enemy" in games can affect how players regard real people.

Media violence has these negative consequences because it increases physiological arousal and excitement, triggers an automatic tendency to imitate hostile or violent characters, primes existing aggressive ideas and expectations, and models social scripts - approved ways of behaving when we're frustrated, angry, or hurt.

Watching more TV violence in childhood is associated with more violent behaviour in adolescence and adulthood (Anderson et al, 2003). Longitudinal study of 700 families, for 17 years showed TV watching in adolescence predicted violence against others in adulthood (Johnson, 2002).

Difficulty of determining direction of causality - aggressive people may just prefer violent TV, thus aggression and TV watching will correlate.