Biological Explanations of

Aggression

The role of neural and hormonal mechanisms in

aggression.

Describe & evaluate how neural &

hormonal mechanisms

influence aggressive behaviour.

Neurotransmitters

Aggression linked to the action of Serotonin & Dopamine

Low levels of Serotonin

High levels of Dopamine

SerotoninNormal levels of Serotonin have

an inhibitory effect on areas

of the brain that are regulated by

Serotonin. Low levels are thought to reduce

the ability to control aggressive impulses leading

to aggressive behaviour.

Support for this hypothesis has been found in a number of studies that either measure levels of Serotonin or manipulate levels of

Serotonin.

After Serotonin has been released it is either reabsorbed by brain cells or broken

down by enzymes.

This process produces waste products. A sample of cerebrospinal fluid is taken and the

level of metabolites is measured.

Low levels of metabolites indicate low levels of

Serotonin.

Studies have found low levels of metabolites in people who have poor impulse control and

engage in aggressive behaviour.

Some studies deliberately manipulate levels of Serotonin.

Mann et al (19900 administerd a drug that reduces levels of Serotonin in the brain to

35 healthy adults.

A questionnaire was given to the participants that assessed their levels of hostility and aggression before and after

the treatment.

This study found that the male participants hostility and aggression rating increased after

treatment with the drug.Coccaro & kavoussi (1997) found that aggression

was reduced after administering the antidepressant drug Prozac.

Evaluation

Aggression may not be caused by low levels of serotonin.

Problems in serotonin metabolism may lead to the development of more receptor sites in the

pre-frontal cortex.

Evidence to support this alternative explanation has mainly come from

post-mortem studies of the brains of people who have committed suicide.

Arora and Meltzer (1989) found that people who had killed themselves

using a very violent method had more serotonin receptor sites in the pre-frontal cortex than a control group

who had not used violent methods.

Mann et al (1996) also found that people who had committed suicide using violent methods

had more serotonin receptors in their pre-frontal cortex.

The well established link between alcohol and aggression may be due to the effect of alcohol on

serotonin.

Badawy (2006) found that alcohol reduces serotonin levels. This reduction may lead to

the aggressive behaviour observed.

DopamineThere is some evidence that there is a link

between elevated levels of dopamine

and dopamine activity in the brain and an increase in aggressive behaviour.

Dopamine agonists that reduce dopamine activity in the brain have been administered to

reduce aggresive behaviour.

One explanation for the effect of dopamine on aggressive behaviour is linked to the effect of

dopamine on reward systems in the brain.

Aggressive behaviour may activate the release of dopamine and generate rewarding feelings.

This reinforces aggressive behaviour: some people may seek out aggressive situations

because it makes them feel good.

Evaluation

Evidence to support the dual role of serotonin and dopamine has mainly

been found in animal studies.

Ferrari et al (2003) conducted an experiment that forced rats to fight at exactly the same time every day for 10 days. On the 11th day

the rats were not allowed to fight and the level of serotonin and dopamine was

measured in their brain.Ferrari found that the rat’s serotonin levels had

decreased and their levels of dopamine had increased.

This shows that consistent aggressive behaviour had changed the rats brain

chemistry.

Hormones

Hormones are chemicals that regulate and control physiological processes.

They also control responses to external threats.

The ‘fight-flight’ response is an example of how hormones control responses to external threats.

Testosterone has been linked to aggression and

aggressive behaviour.

Testosterone is produced by males in the

testes. Women produce

testosterone in the adrenal

glands.

Testosterone produces male

characteristics.

Research on the link between testosterone and aggression has

mainly involved studies using correlational

analysis or the measurement of levels

of testosterone between aggressive and non-aggressive

people.

Archer (1991) conducted a meta-analysis of 5 studies and found a low

positive correlation between testosterone and aggression.

Brook et al (2001) conducted a meta-analysis of 45 studies and found a

mean correlation of + 0.14 between testosterone and aggression.

Olweus et al (1980, 1988) took samples of blood and maesured levels of testosterone from

delinquent male adolescents and ‘normal’ male students.

The researchers found slightly higher levels of testosterone in the delinquent adolescent males than the ‘normal’ male students.

However, the difference was not statistically significant.

Research suggests that higher levels of testosterone is associated with dominance

behaviour rather than aggression.

Some types of dominance behaviour may involve aggression but most do

not.

Evaluation

Research has not found a consistent link between testosterone and aggression.

A few studies have found a strong positive correlation between high levels of testosterone

and high levels of aggression.

However, other studies have found no association.

Bain et al (1987) found no significant differences in testosterone levels and men convicted of

violent and non-violent crimes.

Kreuz and Rose (1972) also found no difference in testosterone levels in a group of 21 prisoners

who had been classified as violent and non-violent.

Furthermore research suggests that testosterone far from causing aggressive behaviour actually

has positive health benefits.

Levels of testosterone in males decline as they get older.

Testosterone supplements have been used successfully to treat age related depression in

males.

McNicholas et al (2003 ) conducted a study of 208 men who had been treated with testosterone replacement therapy and

found statistically significant increases in positive mood and decreases in negative

mood.

Reduction in levels of testosterone are linked to the development of depression in older

males.

Read the handout and answer the

questions