Psychology essay

Neurotransmitters are chemicals that allow impulses from one area of the brain to be transmitted to another area. All behaviours are influences by the actions of neurotransmitters. For example, aggression has been associated with low levels of serotonin, and high levels of dopamine.

It is claimed low levels of serotonin, particularly in the pre-frontal cortex, reduces the ability to control aggressive impulses. Evidence of the role of low levels of serotonin in aggression comes from Mann et al (1990), who manipulated levels of serotonin. They administered the drug dexfenfluramine known to deplete serotonin levels, to 35 healthy adults. They then used a questionnaire to assess hostility and aggression levels, and found these levels had increased among males after treatment with the drug.

In evaluating this, it could be argued that manipulating the levels of serotonin in humans is unethical as this supposedly leads to increased levels of aggression. Furthermore, the research conducted by Mann et al (1990) is on a small sample of 35 adults and is not representative of the wider population, therefore generalizability cannot be achieved.

Conversely, it is believed that high levels of dopamine are associated with aggression.Lavine provides some evidence that suggests increases in dopamine activity are associated with increases in aggressive behaviour. Similarly, Buitelaar et al found the use of dopamine antagonists have been used successfully as a way of reducing aggressive behaviour in violent delinquents.

Research support for the influence of both serotonin and dopamine in aggressive behaviour is provided by Ferrari et al. They allowed a rat to fight every day for 10 days at approximately the same time. On the 11th day, the rat was not allowed to fight, and researchers measured the levels of serotonin and dopamine in its brain. They found in anticipation for a fight, the rat’s dopamine levels had increased and serotonin levels decreased, despite the fact the rat did not fight. This shows that experience had changed the animal’s brain chemistry, preparing for a fight by altering levels of serotonin and dopamine in ways consistent of aggressive behaviour.

However, it is unethical to induce aggression in animals as the action of fighting is likely to cause them pain, to which they cannot consent to. Furthermore, research 

conducted on animals is not representative of humans, therefore results cannot be generalised.

It is also believed that high levels of the hormone testosterone and low levels of cortisol are associated with increased levels of aggression. For example, Kouri et al, using a double blind procedure, gave young men doses of testosterone of a placebo. They were then paired with a fictitious participant an told each member could, by pushing a button, reduce the amount of cash received by the other person. They were then told the other participant was reducing the amount of money they were receiving, and found participants who received testosterone pushed the button significantly more times than those who received the placebo. Moreover, Virkkunen  reported low levels of cortisol in violent offenders.

However, the hormonal explanation fails to consider the positive influence of testosterone. Although it is believed increased levels of testosterone leads to aggression, McNicholas et al found increased in positive mood ad decreases in negative mood with testosterone replacement therapy. Zitzmann also argues that testosterone supplements in older males have been positive and found to enhance vigour and energy. Gender bias is another weakness as most of the research into the link between testosterone and aggression are based on males.

Support for the cortisol link is also provided by McBurnett et al they found that boys with lower cortisol concentrations exhibited three times more aggressive symptoms than boys with higher levels.

However, a weakness of the neural and hormonal explanation of aggression is the fact that most research into the link between neurotransmitters and aggression, and hormones and aggression relies on correlational evidence. Therefore, a causal relationship cannot be established as it is difficult to explain whether low levels of serotonin and high levels of dopamine influence aggressive behaviour, or if they are a by-product of aggression. In the same way it is difficult to explain whether high levels of testosterone and low levels of cortisol are the cause or effect of aggression.

This biological explanation could also be criticised for taking a determinist approach. By suggesting aggression is a result of fluctuating levels of neurotransmitters, the denies the aggressor of free-will and responsibility for their actions.

It is also reductionist as it takes a simplistic view in explaining of the complexity human behaviour as it only represents the nature side of the nature-nurture debate. This provides an unrealistic view of human behaviour because both nature and nurture interact with one another. In fact, aggression is most likely a result of a number of factors, for example, Bandura et al  found social learning had a powerful influence on aggressive behaviour in children.