Post on 19-Jan-2016
transcript
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