Neural Influences
Neural
Biological explanations - aggression is in the biology of the person, not the environment around them.
In the past, people have used this to conclude that castration in highly aggressive males would help them to stop killing/injuring others. This is because violent criminals had high testosterone levels and so castration reduces testosterone levels.
Part of the brain that helps coordinate behaviours which satisfy motivational and emotional urges (e.g. aggression, fear).
2 main parts of this limbic system are:
Amygdala
Allows us to quickly evaluate the emotional importance of sensory information and then respond appropriately.
If certain areas of the amygdala are stimulate in animals, the response is aggression, whereas if they are surgically removed the animal no longer responds to the stimuli previously causing them rage, e.g. Kluver and Bucy (1937): a monkey that was dominant in a social group had its amygdala removed and so the monkey lost its place of dominance in the group.
Hippocampus
Allows us to form LTMs (animals can compare current threats with past experiences and respond appropriately with either aggression or fear.
Impaired function of the hippocampus = nervous system struggles to understand things in a relevant/meaningful context, so the amygdala may respond inappropriately to stimuli = aggressive behaviour. E.g. Boccardi (2010): violent offenders had abnormal hippocampal functioning
Serotonin
neurotransmitter associated with behaviours such as aggression, sleep and depression.
Normal levels help to inhibit activity of the amygdala and so reduce aggression by inhibiting the responses to emotional stimuli that may otherwise lead to an aggressive response.
Low levels remove this inhibitory factor, making it harder to control impulsive/aggressive behaviour (‘serotonin deficiency hypothesis’). Low levels have also been linked to violent suicide.
Some drugs that can alter serotonin levels (increase aggression) include dexfenfluramine which was found to increase hostility and aggression in males (Mann et al., 1990)
Evaluations
Pardini (2014): reduced amygdala volume can indicate development of severe and persistent aggression.
Longitudinal study on 56 male pps from childhood to adulthood. At age 26, some pps who had a history of violence had a brain MRI scan.
Findings: pps with lower amygdala volumes showed higher levels of aggression and violence. THEREFORE, the amygdala is key in evaluating the emotional importance of sensory information. Lower amygdala volume compromises this ability and increases the likelihood is a violent response.
There this shows that the amygdala is important
Ethical and non-invasive
Not a representative sample size
Raine at al (2004) studied 2 groups of violent criminals:
Group 1 = ‘unsuccessful psychopaths’ (been caught and convicted).
Group 2 = ‘successful psychopaths’ (evaded the law).
Group 1 acted more impulsively, hence being caught.
Group 2 were seen as ‘cold, calculating’ criminals.
Group 1's MRI scans showed an asymmetrical hippocampus (different sizes in each hemisphere).
THEREFORE, this asymmetry might prevent the hippocampus and amygdala from working together, and so emotional information isn’t processed accurately - thus resulting in inappropriate responses (physical/verbal).
Raleigh et al. (1991): monkey’s who fed on experimental diets that are high in tryptophan (increases serotonin levels) - showed less aggression, and vice versa.
Rosado et al (2010): 80 dogs (various breeds) referred to Spanish vets because of their aggressive behaviour towards humans. They were compared to 19 dogs (various breeds) that didn’t show this aggressive behaviour.
Aggressive dogs = 278 units of serotonin.
Non-aggressive dogs = 387 unit of serotonin.
(estimate)
THEREFORE, different levels of aggression can be attributed to animals’ serotonin levels.