Neurotransmitters and aggression
Low levels of serotonin - Serotonin in normal levels acts as a calming agent. Low levels therefore make it harder for someone to control their impulsive and aggressive responses.
Support comes from research that has found low levels of the waste product from 5ht in people that display aggressive behaviour.
Mann et al. (1990) gave a drug that reduces serotonin to 35 healthy adults. Questionnaire used to assess hostility and aggression levels. Males (but not females) found to be more aggressive after taking the drug.
High levels of Dopamine - Lavine (1997) increases in dopamine with drugs is associated with increases in aggression. Drugs that lower dopamine have been found to be able to reduce aggression.
Couppis et al. (08) think that dopamine is more of a reinforcer to aggression. Dopamine made in response to please, and so people may act aggressively because of the rewarding sensations that is caused by the increase in dopamine.
Evaluation of Neural mechanisms
Serotonin - found that it might not be how much is in the brain, but our metabolism for it - this will lead to serotonin receptor density. Research into suicides found that those that had more serotonin receptors chose to kill themselves in more violent ways (Mann et al).
Badawy (2006) - low levels of serotonin can explain the well known link of alcohol and aggressive behaviour. Drinking alcohol has a depleting effect on serotonin, which would in turn cause aggressive behaviour in some individuals.
Dopamine - Problems in actually testing it.Mice given a drug which TURNED OFF dopamine levels - caused paralysis due to dopamine's key role in movement. How do we know whether the rats where not aggressive because they had no dopamine, or simply because they couldn't move.
Research support for both Serotonin & Dopamine: Ferari et al. (2003) allowed a rat to fight everyday at same time for 10 days. on 11th day, rat could not fight. However, rat's dopamine levels risen and serotonin dropped in anticipation for the fight.
Hormones - Testosterone
Testosterone doesn't cause aggression, but it makes it more likely. Testo. levels peak in young males then tends to decline with age.
- Research findings:
- Archer 1991 - small meta analysis. Found low positive correlation between levels of testosterone and aggression.
- Book 2001 - larger meta analysis. Found a mean correlation of 0.14.
- Owleus (1988)- could not find any statistically significant difference between testo. in delinquent boys and non-delinquent boys.
Testo. is now thought to be linked more with DOMINACE that is associated with some aggression.
Key research: Kouri et al (1995) - Double blind procedure. Some recieved testo. Told that if they pressed a button they could reduce the amount of cash other person recieved, and thats what other person was doing to them. Testo people pressed it significantly more than non-testo people. Similar study by Pope et al. Same findings.
Hormones - Cortisol
Low levels of cortisol found to be linked with aggressive behaviour.
Research to support: Virkkunen (1985) - low levels of cortisol in frequent violent offenders & Tennes et al. (1985) - in aggresseive school children.
- having a low ANS is uncomfortable, which may cause frustration. Aggressive is a result of that aggression.
- cortisol is thought to inhibit aggression, so low levels will allow for testosterone (and other factors) to have more of an effect.
Evaluation of Hormonal mechanisms.
Testosterone - Inconsistencies in research. Some find a positive correlation, others do not.
- Positive effects of Testo. -
- Zitzmann - aggression and testosterone probably only linked in weightlifters that purposely increase it to stupidly high levels. For others, testo. supplements seems to increase energy and vigour.
- Low levels of testosterone linked with depressive disorders - which also are more likely in older people, when testosterone lowered. Testosterone suppliments have a positive effect in that they rise the mood of people with these distorders.
Cortisol - supported by research, longitudinal study by McBurnett (2000). Found that in boys with lower cortisol exhibited 3x more aggressive symptoms than those with highest cortisol levels at the time of sampling.
Inconsistencies in cortisol research. Some find a positive correlation, others do not. Some even found that HIGHER levels of cortisol linked with more aggression.