Neural & Hormonal Mechanisms in Aggression

• The limbic system is the key structure/region in the brain that is associated with aggression
• The limbic system comprises brain regions and systems that have been widely studied and linked to emotional responses (aggression is a strong emotion marked by a heightened motivation to do harm to another person combined, sometimes, with a lack of fear for the consequences and, at times, for self-preservation)
• Specific brain regions/structures in the limbic system implicated in aggressive behaviour include the hypothalamus, the amygdala, the fornix and parts of the hippocampus

Limbic system structures that are implicated in aggressive behaviour.

• Withdrawal from some drugs such as benzodiazepine has been associated with hostile and aggressive behaviour (Saxon et al. 2010) which could be explained by findings which suggest that benzodiazepine is linked to amygdala activity (Hodges et al. 1987)
• Serotonin is strongly implicated in the control of aggression as it has an inhibitory effect on impulsive behaviour, particularly with regard to the functioning of the prefrontal cortex
• Invivo-molecular neuroimaging research has found that there are associations between impulsive aggression and low serotonin and MAOA levels (Cunha-Bang & Knudsen 2021)

Research which investigates neural mechanisms in aggression

• Farah et al. (2018) - MRI scans revealed that males with alexithymia who also had increased grey matter in their right hemisphere amygdala were more likely to show reactive aggression which could be triggered by their own low/negative mood
• Brunner et al (1993) - males from one family with a dysfunctional MAOA gene (which regulates serotonin production) showed high levels of aggression

Could aggression really be explained neurochemically?

• Testosterone is the main hormone associated with aggression
• Males typically secrete more testosterone than females and males also tend to display more aggression than females (90% of violent crimes and 95% of domestic violence acts are committed by men according to U.S. Department of Justice statistics)
• There is some compelling evidence that aggression and testosterone are linked e.g. Olweus (1985) found that young male offenders were stimulated negatively by testosterone
• Testosterone-related aggression appears to be linked to dominance (Archer 2005) which is a trait more commonly associated with males than with females

Research which investigates hormonal mechanisms in aggression

• Zak et al. (2009) - males with high levels of testosterone were less generous to other males and more likely to punish those who did not reward them i.e. increased testosterone may be linked to antisocial behaviour
• Klinesmity et al. (2006) - male college students who interacted with a gun rather than a children's toy added more hot sauce to a cup of water they believed another student would have to drink i.e. interaction with a gun showed significantly greater increases in their testosterone seen via saliva samples and their aggression (operationalised as the adding of the hot sauce)

Evaluation of neural & hormonal mechanisms in aggression

Strengths

• The use of SSRIs which regulate and promote serotonin levels have been shown to reduce aggression (Bouvy & Liem 2012)
• Prisoners who had committed violent crimes showed higher testosterone levels than those who had committed theft, plus these violent criminals also violated more rules, particularly rules involving overt confrontation (Dabbs et al. 1995)

Weaknesses

• Testosterone cannot be said, conclusively to cause aggression as the evidence is only correlational
• Both neural and hormonal explanations of aggression ignore key social/environmental factors as being of relevance to aggressive behaviour e.g. upbringing, education, substance abuse

Link to Approaches:

Neural and hormonal explanations of aggression are clearly part of the Biological Approach as they assume that physiological processes are a key influence on behaviour.

Link to Issues & Debates:

Biological explanations tend to be reductionist in their scope i.e. they attempt to explain a complex behaviour such as aggression in ways which reduce it to a simple case of brain functioning/hormone levels. While this can be helpful as it enables researchers to focus on just one, clear variable (which can be objectively measured by, for example, saliva samples or brain-scanning) it does not fully acknowledge the important role played by non-biological factors in behaviour.

Biological explanations can also tend towards being deterministic as they may assume that, for example, males with high testosterone are bound to behave aggressively, ignoring the role of free will and the ability of human beings to learn from mistakes and to actively modify their behaviour.