Medicine:Brain lesion theory

The term Brain lesion theory is a colloquialism which generally refers to the idea that brain lesions and traumatic brain injury are associated with aggressive and violent behaviour, criminality and anti-sociality . The concept of a correlation between brain injury and violent or aggressive behaviour has a strong basis in scientific literature and has been explored across multiple disciplines including forensics, psychology and sociology. Most findings in psychology suggest that the correlation between brain injury and aggression is specific to frontal lobe injury. There’s is little evidence to suggest that damage to other areas of the brain correlates with aggression.

The correlations between frontal lobe injury and aggression have important implications in terms of function localisation in the brain. Function localisation is the idea that certain functions are specific certain areas of the brain. There is evidence to suggest that the frontal lobe is responsible for the control of cognitive skills like judgment and emotion regulation. Consequently, damage to the frontal lobe may lead to loss of control and impairment in social/emotional judgement therefore reducing a person’s ability to inhibit negative emotion and as a consequence increase aggressive responses.

However, it is important to note that the evidence for a correlation between frontal lobe injury and aggression is heavily based on case study and consequently cannot be used to imply a causal factor in either direction. Further, aggression, violence and anti-sociality also correlate with alcoholism, abuse and a number of psychological, environmental and biological factors thus even if there was evidence for a causal link between brain injury and aggression it cannot be concluded that brain injury alone causes aggression.

Background

Though frequently presented in highly distorted form, the case of Phineas Gage was perhaps the first to suggest the brain's role in determining personality and that damage to specific parts of the brain might induce specific personality changes.

The Frontal Lobe and Aggression

The Frontal lobe is separated into different cortices involved in emotion regulation, inhibition and decision making, consequently when it is damaged these abilities are reduced resulting in aggressive behaviour. The Orbital-frontal cortex specifically is the area involved in incorporating negative emotion in decision making when it is contextually relevant and inhibiting it when it is contextually irrelevant. Damage to the Orbital-frontal cortex inhibits this ability and could as a consequence lead to the incorporating of negative emotion in decision making when it is irrelevant resulting in increased aggressive or violent behaviour. A review of research papers concerning abnormal frontal lobe function and violent crime found an association between the orbital-frontal cortex and "poor impulse control, explosive aggressive outbursts and inappropriate verbal lewdness" suggesting that frontal lobe injury does influence aggression. The ventromedial frontal cortex is an area of the brain that regulates emotion and behaviour. It plays a vital role in facial emotion recognition. People with lesions to the ventromedial frontal cortex have difficulties recognising emotion in other people which influences their likelihood to engage in aggressive behaviour because they can misinterpret harmless behaviour like sarcasm for malicious behaviour and respond aggressively when it is unwarranted.

Evidence for the correlation between frontal lobe injury and violence

Brower and Price (2001) conducted a meta-analysis of research literature to evaluate the evidence for a relationship between frontal lobe function and violent behaviour. The evidence for the correlation between frontal lobe injury and violence can be categorised into three types of evidence; Clinical, Neurological and Neuropsychological.

Clinical Evidence

Clinical evidence is based on a series of observations made by psychologists and psychiatrists in a clinical setting.

Bower and Price (2001) assessed scientific literature on clinical frontal lobe disorders and violence and found that across all clinical observations people with frontal lobe injury showed impairments in judgment, awareness of socially appropriate conduct and the capacity to assess future consequences. In one study adults who acquired frontal network damage before eight years olds demonstrated recurrent impulsive, aggressive, and antisocial behaviour. Their behaviour was associated with primary deficits in tests of executive function, poor abstract conceptual thinking, immature moral reasoning and an inability to envision another person’s subjective experience as adults all of which are functions specific to the frontal lobe that are impaired when it is damaged.Consequently, the aggression observed in a clinical setting is consistent with aggression that someone with poor executive function would be unable to control. However, because this study relied heavily on clinical observation it cannot be used to suggest the brain injury causes aggression.

Another clinical study that observed the link between frontal lobe injury and aggression was The Vietnam Head Injury Study; a notable study of war veterans with traumatic head injury. The study assessed veterans with traumatic head injury including people with lesions specifically to the frontal lobe, results indicated that veterans with lesions only to the frontal lobes demonstrated more aggressive and violent behaviour compared to veterans with non-frontal head injury and controls without head injury. They also found a significant correlation between an increase in aggression and orbital frontal injury as identified by CT brain scans. The damage to the frontal lobe, specifically the orbital frontal cortex suggests difficulties with impulse control and difficulties managing emotions which explains the correlation with aggressive and violent behaviours. Although it is important to consider other biological, psychological and social factors, like PTSD that may have come into play to influence the incidence of aggressive behaviours.

Neurological evidence

Neurological evidence is based on changes in neural network activity in the brain correlating with aggression.

Brower and Price (2001) analysed a trial that measured electroencephalogram (EEG) activity in participants who demonstrated aggressive behaviour and non-aggressive participants. They showed that participants who presented antisocial and aggressive behaviour had abnormal electrical brain patterns in the frontal lobe compared to the control group. Abnormal frontal lobe EEG's correlate with violent behaviours although causality has not been determined.

Further, Brower and Price (2001) noted that in a study of 333 prisoners who committed a violent crime and didn't have structural brain damage, there was a correlation between abnormal frontal EEG activity and recurrent physical aggression. Results indicated that 62.2% of participants who committed repeated violent behaviour demonstrated EEG abnormalities compared to 11.8% of other subjects who committed a single violent offence, this suggests a fundamental link between frontal lobe abnormalities and violence.

In another study, that compared positron emission tomography (PET) brain scans of forensic psychiatric patients to normal controls, forensic psychiatric patients had reduced blood flow in the frontal cortex. This was associated with repeated aggressive behaviour. Further when PET scans were performed on people charged with murder, people charged with murder compared to controls showed statistically significant bilateral prefrontal metabolic decreases during a frontal lobe activation task. This is evidence for a correlation between abnormal prefrontal cortices and violence however it doesn’t imply that these abnormalities caused behaviour associated to the murder. It is important to note these patients likely had other factors that contributed to their aggressive behaviour besides abnormalities in the frontal cortex.

Neuropsychological evidence

Neuropsychological evidence is based on the influence of neurological factors on psychological factors relevant to aggression.

In two separate studies mentioned in Brower and Price’s (2001) meta-analysis, there was evidence for a correlation between decreased performance on executive function tests and increased aggression in a sample of male participants who had no history of neurological or psychiatric abnormalities including substance addiction or misuse. In a third study also analysed by brower and price low scores on executive function tasks in boys ages 10–12yrs with paternal histories of substance misuse significantly predicted aggression.

Since the frontal lobe is responsible for executive function, decreased performance of executive function tests suggests issues with the frontal lobe and consequently and association between decreased executive function performance and aggression suggests a link between frontal lobe malfunction and aggression.

Evidence against the correlation between frontal lobe injury and aggression

Although there is a correlational link between brain injury and aggression, frontal lobe injury is not necessarily a causal element of aggression since a large number of people who suffer brain injury do not engage in aggressive behaviours. There are multiple complex aspects that come into play alongside the correlation of brain injury and aggression. There have been some studies that have found no significant correlation between Traumatic Brain Injury (TBI) and aggression.

A 2003 study conducted by Tuekstra, Jones and Toler to assess whether the incidence of TBI will be higher in people convicted of violent crimes compared to non-violent crimes from the same social economic status found no significant difference in the incidence of Traumatic Brain Injury between the two groups. However, there was a significant difference in the cause and severity of injury. People convicted of violent crime on average had more severe brain injuries as a result of abuse whereas people convicted of nonviolent crime had less severe sports related injuries. People convicted of violent crime also had higher reports of changes in behaviour following injury. These findings can be interpreted to suggest that severity of injury can influence whether the person exhibits more aggressive changes in behaviour. Moreover, the results of this study suggest that a number of factors come into play in terms of the incidence of violence and brain injury including severity of the injury and premorbid factors relevant to the injury. Since majority of the people convicted of violent crimes acquired brain injury as a result of abuse, the correlation of violence and injury be related to premorbid factors including the psychological trauma associated with abuse

Consequently it is important to consider other factors that contribute to aggressive behaviours in people with and without traumatic brain injuries including abuse,substance misuse, poor school performance, poverty, trauma and other psychological issues and previous histories of aggression.

Aggression and Violence
Aggression	Violence Criminal Activity Psychopathy Theory of Aggression
Brain Injury	Frontal lobe Injury Traumatic brain injury Ventromedial Cortex Orbital frontal cortex
Types of evidence	Case studies
Other factors related to aggression	History of abuse Alcoholism Poverty Psychological disorders