Hostility is a form of aggression. Aggression is categorized as predatory or affective; in the predatory form, aggression is used by predators to capture prey. In animals, affective aggression is marked by vocalization, hair standing on end and other signals that are intended to frighten an enemy away.
Humans also exhibit affective aggression in the form of hostile behavior. This type of aggression is regulated by the prefrontal cortex, amygdala, hypothalamus, thalamus and midbrain.
Amygdala
The amygdala is an area of the brain linked to fear, according to NeuroPsychiatryReviews.com. It is a small section of tissue localized in the temporal lobe of the brain.
Its importance in contributing to aggressive behavior was first recognized by Austrian neurosurgeon Karl Pribram, who used rhesus monkeys to show that destruction of this area of the brain resulted in an abnormal decrease in agitated behavior associated with social hierarchy, says the "Journal of Comparative Physiological Psychology." Furthermore, functional imaging studies have shown that exposure to threatening stimuli increases activity in the amygdala, says NeuroPsychiatryReviews.com.
Hypothalamus
The hypothalamus is a relatively small structure located near the upper portion of the brain stem. It is responsible for regulating the sympathetic and parasympathetic reactions of the autonomic nervous system. This includes regulating heart rate, pupil dilation and digestion. Stimulation of the medial hypothalamus elicits affective aggression, as was shown by experiments at the Yale University Medical School.
Periaquaductal Gray Matter
The periaquaductal gray matter, or PAG, is an area found in the midbrain. It receives input from the medial hypothalamus and has been shown to induce aggressive behavior when electrically stimulated. Additionally, damage to the tissues of the PAG results in the inhibition of aggression.
Thalamus
The thalamus is associated with hostility triggered by sensory stimulation. The thalamus acts as a gateway for sensory information entering the brain, routing it to the appropriate areas of the cerebrum. It is thought that rage can be triggered by thalamic activation of the amygdala.
Prefrontal Cortex
The prefrontal cortex is an area of the brain important for reasoning and decision-making. It is thought to be important in inhibiting aggressive behavior triggered by activation of the amygdala. Individuals who have suffered injury to the prefrontal cortex exhibit anti-social behavior and lack of empathy, according to the National Academy of Sciences.
References
- Treating Aggression: Which Agents Work--And How to Choose Among Them
- "Neuroscience: Exploring the Brain (3rd Edition)"; Mark Bear, Barry Connors and Michael Paradiso; 2007
- "Journal of Comparative Physiological Psychology"; Influence of amygdalectomy on social behavior in monkeys."; Rosvold, Mirsky and Pribram; June 1954
- "Science"; Neural Pathways Associated with Hypothalamically Elicited Attack Behavior in Cats; Carl Chi and John Flynn; February 1971
- "Proceedings of the National Academy of Sciences"; Evidence for a dysfunctional prefrontal circuit in patients with an impulsive aggressive disorder; Mary Best, J. Michael Williams and Emil Coccaro; June 2002
