Rage: an Innate Brain System
When we think of rage, we often think of crime, and then guilt. In doing this, we fail to recognize that rage is an innate emotional system in the human brain that contributes to our survival. Stimulating specific neurocircuitry evokes rage in laboratory animals. Physical brain damage and seizures can certainly affect how this innate neurocircuitry operates and sometimes makes rage neurocircuitry more responsive, more automatic. Moreover, evidence indicates that extremely negative experiences can result in physiological changes in the brain that may predispose one to bouts of rage.
In Guilty by Reason of Insanity: A Psychiatrist Explores The Minds of Killers (1998), Dorothy Otnow Lewis describes the brain of a convicted killer, Lucky, who savagely stabbed a store clerk.
The lesions between the cortex of the frontal lobes and the rest of the central nervous system, between the self-reflective portions and the more instinctual portions of the brain, also contributed to Lucky's episodic violence. In some ways, his actions were like those of a decorticate cat. When the cortex of a cat is separated surgically from the rest of the brain, leaving only the lower centers of the brain intact, the cat may at first glance appear normal. In fact, it will purr and respond positively to affection. However, its responses to stimuli that ordinarily would cause expressions of mild discomfort or annoyance are no longer moderated by the frontal cortex. The decorticate animal, when stimulated, becomes ferocious, directing its attack at anything it perceives as threatening or uncomfortable.
Regarding how negative experience affects the brain, Lewis writes:
What fascinates me most is the fact that brain concentrations of substances like serotonin are not immutable. They are not simply genetic givens—experience affects them. Certain kinds of stressors can decrease brain serotonin levels and thereby change behavior. For example, if you isolate animals at crucial developmental stages, if you keep them caged all alone, their serotonin drops. What is more, when you then release them and put them in contact with other animals, they are fiercely aggressive. Pain and fear also reduce serotonin levels and promote aggression. That's how pit bulls are trained to fight. Heat, crowding, discomfort, and upbringing by aggressive members of a species all increase animal aggressiveness. …
It seems that aggression, in its varied forms, arises from very different neural circuits in the brain. In Affective Neuroscience: The Foundations of Human and Animal Emotions (1998), Jaak Panksepp explains that scientists applying electrical stimulation to "slightly different brain zones" in laboratory animals evoke three distinct kinds of aggression. 1) predatory aggression, 2) rage-like aggression, and 3) inter-male aggression or dominance aggression. Panksepp points out that "prolonged social isolation or hunger may increase all forms of aggression, while high brain serotonin activity may reduce them all."
Circuitry that prompts aggression is quite specific. Panksepp explains that quiet-biting attack is typically evoked during electrical stimulation of the dorsolateral hypothalamus while rage-driven aggression is typically evoked during electrical stimulation of the ventrolateral and medial hypothalamus.
Electrical stimulation to SEEKING system locations in rats and cats prompt different behaviors. Panksepp writes: "The species-typical expressions of this system lead to foraging in some species and predatory stalking in others." Stimulating this system in cats results in predatory stalking and quiet-biting attack. "Obviously, this is a reasonable species-typical SEEKING behavior for a carnivorous animal that subsists at the top of the food chain."
Panksepp points out that when scientists stimulate specific circuits for rage-driven aggression in humans, the subjects report "experiencing a feeling of intense rage." When rats are stimulated in specific RAGE neurocircuits, they will attempt escape. Panksepp explains that most animals have "unpleasant affective experiences" during electrical stimulation to RAGE neurocircuits in their brain. He observes that such animals "exhibit piloerection, autonomic arousal, hissing, and growling," and readily learn to turn the stimulation off. He points out that these animals direct their anger towards anything in their environment perceived as a threat, even members of their own species.
In addition to innate circuitry for predation, rage, and dominance, Panksepp discusses how animals develop a kind of "defensive" aggression which "emerges largely from a dynamic intermixture of RAGE and FEAR systems." He also draws attention to innate "appeasement" behaviors." An animal that lies on it's back and exposes vulnerable parts like the belly and neck can often reduce aggression by others of the same species. Sometimes the appeasement signal is vocal. Panksepp writes: "Defeated rats often emit long 22 Khz vocalizations."
Panksepp also categorizes infanticide as a form of aggression although pinpointing specific circuitry for this kind of behavior is not so easy. In the animal world, especially including rats, it seems that males sometimes kill the offspring of another male in order to stop lactation in the female mother, restoring her reproductive abilities. The new male is thus able to more quickly mate and produce his own offspring. "Considering that female rats have a three-week gestational period," Panksepp writes, "it was anticipated that the pup-killing tendencies of males might diminish approximately three weeks after mating, at about the time their own offspring might be born." He explains that research in the laboratory indicates that this is exactly what happens. Panksepp points out two other motivators of infanticide: "A mother may kill and consume some of her own offspring if food is scarce, even though such killing can also occur for more subtle 'political' reasons. Perhaps the most famous perpetrators of such acts were the cruel female chimpanzees, Passion and her daughter Pom, who killed off at least three and probably more of the young infants of other females in the group that Jane Goodal studied for many years."
A very interesting observation that Panksepp makes relates to genetic transmission of aggression. He points out that "genetic selection experiments in both male and female rodents indicate that one can markedly potentiate aggressiveness through selective breeding within a half dozen generations, and that breeding for aggression is as effective in females as in males."
In Affective Neuroscience, Panksepp points to the work of Walter Hess during the 1930s in determining that electrical stimulation to certain brain areas can produce rage behavior in animals. Hess won the Nobel Prize in 1949. Panksepp writes: "It has long been known that one can enrage both animals and humans by stimulating very specific parts of the brain, which parallel the trajectory of the FEAR system." He adds: "Brain tumors that irritate the circuit can cause pathological rage, while damage to the system can promote serenity."
Panksepp writes: "The core of the RAGE system runs from medial amygdaloid areas downward, largely via the stria terminalis [a bundle of nerve fibers] to the medial hypothalamus, and from there to specific locations within the PAG [periaqueductal gray] of the midbrain."
In the illustration to the left (links to source), the amygdala is labeled on the right and the thin string-like stria terminalis, also labeled on the right, links the amygdala to the hypothalamus, which lies hidden beneath the thalamus in this illustration. Although not labeled, the periaqueductal gray lies in the yellow center area that represents the midbrain.
Regarding the kinds of stimuli that can access RAGE circuitry, Panksepp points to such things as body surface irritation or when one does not receive an expected reward. He explains that the most common triggers of rage "are the irritations and frustrations that arise from events that restrict freedom of action or access to resources." He points out that "a human baby typically becomes enraged if its freedom of action is restricted simply by holding its arms to its sides." Activation of RAGE circuits is "accompanied by an invigoration of the musculature, with corresponding increases in autonomic indices such as heart rate, blood pressure, and muscular blood flow." According to Panksepp, the phrase "getting hot under the collar," is accurate in that body temperature also increases during rage.
In the image below left, the medial hypothalamus is labeled in red lettering. This image is from S.S. Nussey and S.A. Whitehead, Endocrinology, NCBI bookshelf (image links to source). For some perspective, the image below right depicts the location and relative size of the hypothalamus as a whole (image links to source).
RAGE circuitry is organized hierarchically. Lesions of higher areas such as the amygdalae do not diminish responses from lower areas, while damage to lower areas such as the medial hypothalami and periaqueductal gray zones dramatically diminishes rage evoked from the amygdalae.
The image below (links to source) illustrates the position of the periaqueductal gray of the midbrain and is taken from professor Robert Lynch's course, "Territoriality and Aggressive Behavior," at the University of Colorado at Boulder.
According to Panksepp, the following areas provide input to the periaqueductal gray (PAG), a sort of primary generator for RAGE circuitry. Panksepp emphasizes that most of these connections are reciprocating two-way circuits.
Areas of the frontal cortex containing reward-relevance neurons influence RAGE circuitry.
Cortical areas called frontal eye fields, which help direct eye movements to especially prominent objects in the environment, influence RAGE circuitry.
The orbitoinsular cortex, especially the insular area—where a multitude of senses converge including pain and perhaps hearing—may provide specific sounds direct access to RAGE circuitry. In humans, these sounds may include, for example, an angry voice.
The medial hypothalamus provides powerful input related to energy (food) requirements and sexual matters thus influencing RAGE circuitry activated in pursuit of such resources.
A lower area, the vestibular complex, may help enrage animals when their bodily orientation is disturbed.
Cell groups such as the norepinephrine-producing loci coerulei and serotonin-producing raphe nuclei, which exert modulatory control over all behaviors, also influence RAGE circuits.
The nucleus of the solitary tract, which collects information via the vagus nerve that is probably related to processes such as heart rate and blood pressure, inputs to RAGE circuitry.
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