Aggression: Its Types and Neurobiology

Psychologically, the term aggression runs the gamut of behaviors that can result in both physical and psychological harm to ourselves, others or objects in the environment.

We call people aggressive when they yell at or hit each other, when they cut off other cars in traffic, or even when they smash their fists on the table in frustration. On the contrary, the injuries that sports players receive during a rough game or the killing of enemy soldiers in a war might not be viewed by everyone as aggression.

So it is difficult to define aggression. The social psychologists, judges, politicians and many others have spent a great deal of time trying to determine what should and should not be considered aggression.

Social psychologists define aggression as behavior that is intended to harm another individual, who does not wish to be harmed. It involves the perception of intent and, therefore, what looks like aggression from one point of view may not look that way from another, and the same harmful behavior may or may not be considered aggressive depending on its intent. Nevertheless, intentional harm is perceived as worse than unintentional harm, even when the harms are identical.

Social psychologists use the term violence to refer to aggression that has extreme physical harm, such as injury or death, as its goal.

Types of aggression –

Impulsive or emotional aggression – It occurs with only a small amount of forethought or intent and is determined primarily by impulsive emotions.

Instrumental or cognitive aggression – It’s aggression that is intentional and planned. Instrumental aggression is more cognitive than affective and may be completely cold and calculating.

Emotional aggression is usually treated differently in the legal system, having less severe consequences than instrumental aggression. In fact, all aggression is at least in part instrumental because it serves some need for the perpetrator.

The following categories of aggression fall under the above types -

• Physical aggression - It involves harming others physically, for instance, hitting, kicking, stabbing, or shooting them.
• Nonphysical aggression - It doesn’t involve physical harm but includes verbal aggression such as yelling, screaming, swearing, and name-calling.
• Nonverbal aggression - It occurs in the form of sexual, racial, and homophobic jokes and epithets, which are designed to cause harm to individuals.
• Relational or social aggression – It is defined as intentionally harming another person’s social relationships, for instance, by gossiping about another person, excluding others from our friendship, or giving others the silent treatment.

Factors responsible for aggression –

Genetic factors - Twin and family studies suggest that impulsive aggression has substantial heritability. Individuals with a biological risk for aggression may be particularly vulnerable to the effect of psychosocial adversity. Women are less likely to engage in physical aggression but they do use non-physical forms, such as verbal aggression, relational aggression, and social rejection.

Environmental factors - Environmental factors comprise familial factors that include observing or experiencing aggression as a child or adolescent as well as cultural and socioeconomic factors that are conducive to aggression. People, who grow up witnessing more forms of aggression, are more likely to believe that such violence and hostility are socially acceptable.

Physical factors – People, who have epilepsy, dementia, psychosis, alcohol abuse, drug use, and brain injuries or abnormalities, are more likely to indulge in aggression.

The interactions of genetic, environmental and physical factors play a major role in aggression and antisocial behaviors.

Neurobiology of aggression –

Impulsive verbal and physical aggression can be associated with a variety of psychiatric disorders and are frequently seen in personality disorders, such as borderline and antisocial personality disorders. The consequences of these behaviors can be serious and include spousal abuse and injury, job loss, criminal assault, rape or murder.

Brain parts responsible for aggression -

It is now known that aggression is generally associated with impairments in several cognitive systems such as the abilities to resist impulses, to modulate behavior and to understand the consequences of behavior.

The neural basis for these cognitive skills resides in the prefrontal cortex. The term executive function is used to encompass the high-level cognitive skills needed to navigate through a world full of stressors and distractions while remaining focused on a task and suppressing impulses that may not be in one’s best interest.

In healthy individuals, the prefrontal cortex serves to modulate behavior. For example, functional imaging studies have shown activation of the ventromedial prefrontal cortex during tasks that require the suppression of aggressive impulses. By contrast, individuals with impairment of prefrontal function may have the inability to control impulses.

Neuropsychological tests have found impairment in executive function in adolescent and adult offenders. Imaging studies, both structural (MRI) and functional, have shown high rates of abnormality in aggressive people with reduced volume and metabolism of the prefrontal cortex.

Before the recognition of the role of prefrontal areas, it was felt that aggression arose from the involvement of the amygdala and other structures of the limbic system. This phylogenetically ancient structure is the seat of emotion, the site in which emotional responses register and are modulated.

Therefore, pathological aggression results from an interplay of impairment in areas of the brain that modulates both emotional reactivity and the effect of environmental stimuli.

Brain signal mechanism responsible for aggression -

The signaling mechanism in the brain shapes our social behavior. Activity within the brain is mediated by circuits made up of excitatory neurons, which ramp up activity, and GABA-ergic interneurons, which inhibit and quieten the excitatory activity.

Duke-NUS researchers have discovered that a growth factor protein, called brain-derived neurotrophic factor (BDNF), and its receptor, tropomyosin receptor kinase B (TrkB) affects social dominance in mice. Due to the loss of BDNF-TrkB, GABA-ergic interneurons in these transgenic mice supplied weaker inhibition to surrounding excitatory cells, which became overactive.

The transgenic mice, in which the TrkB receptor was removed specifically in the GABAergic interneurons in the area of the brain regulating emotional and social behavior, known as the corticolimbic system, exhibited unusual aggressive behavior when housed together with normal mice.

The findings may have implications for better understanding social hierarchies, aggression, and bullying.

The bottom line –

There has been an increasing trend of occurrence of different types of aggressive behaviors by people all over the world. This disturbing trend has been robbing the society of its peace and, therefore, has unpleasant consequences that are apparent in all domains of our life.

Given the heavy societal cost of bullying and aggression, a better understanding of its causes is a step towards their effective prevention and treatment.

References -

• Neurobiology of Aggression and Violence Larry J. Siever M.D.Published Online:1 Apr 2008https://doi.org/10.1176/appi.ajp.2008.07111774

• Duke-NUS Medical School. "The neurobiology of social aggression." ScienceDaily. ScienceDaily, 19 October 2018. <www.sciencedaily.com/releases/2018/10/181019100549.htm>.